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Halteres

Halteres (singular halter or haltere) (from ἁλτῆρες, hand-held weights to give an impetus in leaping) are a pair of small club-shaped organs on the body of two orders of flying insects that provide information about body rotations during flight. Insects of the large order Diptera (flies) have halteres which evolved from a pair of ancestral hindwings, while males of the much smaller order Strepsiptera (stylops) have halteres which evolved from a pair of ancestral forewings.

Halteres oscillate rapidly along with the wings and operate like vibrating structure gyroscopes: any rotation of the plane of oscillation causes a force on the vibrating halteres by the Coriolis effect. The insect detects this force with sensory organs called campaniform sensilla and chordotonal organs located at the base of the halteres and uses this information to interpret and correct its position in space. Halteres provide rapid feedback to the wing-steering muscles, as well as to the muscles responsible for stabilizing the head.

Background
The majority of insects have two pairs of wings. Flies possess only one set of lift-generating wings and one set of halteres. The order name for flies, "Diptera", literally means "two wings", but there is another order of insect which has evolved flight with only two wings: strepsipterans, or stylops; they are the only other organisms that possess two wings and two halteres. The strepsipterans have adapted their forewings into halteres, whereas dipterans have adapted their hindwings into halteres. This unique structure which detects rotations/perturbations during flight has never been described in nature elsewhere, though many flying insects have been shown to detect Coriolis forces from their non-specialised wings.

Halteres are able to sense small deviations in body position using the gyroscopic properties of moving mass. What this means is that halteres beat up and down in time with the flapping of the wings along a linear pathway, but when the fly's body begins to rotate, the path of the beating halteres also changes. Now, instead of the halteres following a linear path, they begin to follow a curved path. The larger the perturbation they experience, the farther the halteres move from their original linear path. During these periods, the haltere is no longer moving in only two directions (up and down), but four (up, down, left, and right). The force exerted on the halteres in response to this left right movement is known as Coriolis force and can be produced when any moving object is rotated in the three directions of rotation, yaw, pitch or roll (see figure). When this occurs, tiny bell-shaped structures at the base of the haltere experience strain as the haltere stalk bends in their direction. The nervous system can then transform the bending of these hairs into electrical signals, which the fly interprets as body rotation information. The fly uses this information to make corrections to its position and thereby restabilizes itself during flight. Further details explaining the dynamics and physiology of halteres are described below.

Halteres are typically only associated with flight stabilization, but their ability to detect body rotations can elicit compensatory reactions not only from the wing steering muscles, but also from neck muscles which are responsible for head position and gaze. Halteres may also be useful for other behaviors. Certain species of flies have been observed to oscillate their halteres while walking in addition to oscillating them during flight. In these individuals, halteres could thus be detecting sensory information during walking behavior as well. When the halteres are removed, these insects perform more poorly at certain walking challenges. However, how haltere information is processed and used during walking remains, with few exceptions, unclear. Specific examples of what has been found are described below.

History
Halteres were first documented by William Derham in 1714. He discovered that flies were unable to remain airborne when their halteres were surgically removed, but otherwise behaved normally. This result was initially attributed to the haltere's ability to sense and maintain equilibrium. In 1917 v. Buddenbrock asserted that something else was responsible for the flies' loss of flight ability. He claimed that the halteres should instead be considered "stimulation organs". In other words, that the activity of the halteres energized the wing muscular system, so that they acted as an on/off switch for flight. V. Buddenbrock attempted to show that activation of the halteres would stimulate the central nervous system into a state of activity which allowed the wings to produce flight behavior. It has since been concluded that this is not in fact true, and that the original assertion that halteres act as balance organs is the correct one. V. Buddenbrock was able to show that immediately after haltere removal flies were unable to produce normal wing movements. This was later explained by the fact that allowing flies a few minutes recovery time post-surgery resulted in total recovery of normal flight muscle control. Further, in an interesting side experiment performed by Pringle (1938), when a thread was attached to the abdomen of haltereless flies, relatively stable flight was again achieved. The thread in these experiments presumably aided in keeping the fly from rotating (similar to the way a heavy basket below a hot air balloon prevents the balloon from tipping), which supported the hypothesis that halteres are responsible for sensing body rotations.

The original balancer theory, which was postulated by Pringle (1948), only accounted for forces produced in two directions. Pringle claimed that yaw was the only direction of rotation that flies used their halteres to detect. Using high speed video analysis, Faust (1952) demonstrated that this was not the case and that halteres are capable of detecting all three directions of rotation. In response to this new discovery, Pringle reexamined his previous assumption and came to the conclusion that flies were capable of detecting all three directions of rotation simply by comparing inputs from the left and right sides of the body. Of course, this is not the actual mechanism by which flies detect rotation. Different fields of sensory organs located in different regions at the base of each haltere detect the different directions of rotation, which also explains why flies with one haltere are still able to fly without issue.

Evolution
It is generally accepted that the halteres evolved from the non-flight wings of insects – the hind-wings of Diptera and the fore wings of Strepsiptera respectively. Their movement, structure, function and development all support this hypothesis. Characterizations of the arrangement of sensory organs known as campaniform sensilla, found at the base of the haltere, show many similarities to those found at the base of the hindwings in other insects. The sensilla are arranged in a way so similar to that of hindwings, that were the halteres to be replaced with wings, the forces produced would still be sufficient to activate the same sensory organs. Genetic studies have also brought to light many similarities between halteres and hindwings. In fact, haltere development has been traced back to a single gene (Ubx), which when deactivated results in the formation of a hindwing instead. Because just a single gene is responsible for this change, it is easy to imagine a small mutation here leading to the formation of the first halteres.

Convergent evolution
Though no other structure with entirely the same function and morphology as halteres has been observed in nature, they have evolved at least twice in the class Insecta, once in the order Diptera and again in Strepsiptera. Another structure in the class insecta also exists whose primary function is not the same as halteres, but that additionally serves a similar balancing function. This occurs in the order Lepidoptera and refers to the antennae of moths and butterflies.

Strepsipteran haltere
Strepsipterans are a unique group of insects with major sexual dimorphism. The females spend their entire lives in a grub-like state, parasitizing larger insects. The only time they ever come out of their host insect is to extend their fused heads and thoraces for males to notice. The males are also parasites, but they eventually will leave their host to seek their female counterparts. Because of this, they still retain the ability to fly. Male strepsipterans uniquely possess two hindwings, while their forewings have taken on the club-like form of halteres. Though strepsipterans are very difficult to locate and are additionally rather short-lived, Pix et al. (1993) confirmed that the specialized forewings that male Strepsiptera possess perform the same function as dipteran halteres. Rotational movements of the body combined with the oscillating halteres produce Coriolis forces that can be detected by fields of mechanosensors (campaniform sensilla) located at the base of the halteres. Using functional morphology and behavior studies, Pix et al. showed that these sensors then transmit body position information to the head and abdomen to produce compensatory movements. For simplicity, the remainder of this article will refer only to dipteran halteres.

Lepidopteran antennae
Certain lepidopterans (moths and butterflies) exhibit small amplitude oscillation of their antennae at constant angles during flight. Antennal movements in lepidopterans were originally hypothesized to aid in wind or gravity perception. A study performed using the hawk moth, Manduca sexta, confirmed that these tiny, antennal oscillations were actually contributing to body rotation sensation.

Sane et al. (2007) determined that antennae were responsible for flight stabilization in hawk moths by removing the long part of the antenna (the flagellum), then reattaching it to determine its influence on flight performance. When the flagella were removed, the moths were no longer able to maintain stable flight. After reattachment of the flagella, flight performance was restored. The source of this difference was determined to be mechanosensory. There are two sets of mechanosensory organs located at the base of the lepidopteran antenna, Böhm's bristles and the Johnston organ. These fields of receptors respond to different directions of antennal movements. Antennae are also capable of sensing odor, humidity, and temperature. Sane et al. (2007) was able to demonstrate that it was the mechanosensors that were responsible for flight stability as opposed to the other sensory organs, because when the flagella were removed and then reattached, all antennal nerves were severed excluding those at the base (Böhm's bristles and the Johnston organ).

Genetics
In segmented organisms there are genes called Hox genes, which determine the development of serial homologs, or repeating structures within an organism (e.g. jointed appendages of arthropods or vertebrae in mammals ). In insects, the thorax is separated into different segments. One of the things that the Hox gene Ultrabithorax (Ubx) is responsible for, is specifying the identity of the third thoracic segment of their body. Proper hindwing development in a number of insect species is dependent on Ubx, including butterflies, beetles, and flies. In fruit flies, (Ubx) is responsible for the formation of the halteres during metamorphosis. If this gene is experimentally deactivated, the haltere will develop into a fully formed wing. This single homeotic gene change results in a radically different phenotype, but also begins to give us some insight into how the ancestors of flies' hindwings may have originally evolved into halteres.

Though it is clear that Ubx is the primary gene responsible for hindwing formation, Ubx also regulates other genes once expressed. Weatherbee (1998) postulated that differences in Ubx expression patterns or levels may not be responsible for the observed physiological changes. Instead, he suggested that Ubx-regulated target gene sets were the direct source of the observed changes. Several Ubx-regulated target genes have been identified, including two direct targets, spalt and knot, which are expressed in the wing and repressed in halteres, and which are not affected by extradenticle. Other genes which are expressed in wings and repressed in halteres have also been identified, but whether or not they act as direct targets of Ubx regulation are still unknown.

Dynamics

Dipteran insects along with the majority of other insect orders use what are known as indirect flight muscles to accomplish flight. Indirect insect flight muscles are composed of two sets of perpendicular muscles (see left figure) that are attached to the thorax (instead of directly to the wing base as is the case for direct flight muscles). When the first set of muscles contracts, they deform the body of the insect and compress its thorax vertically, which lifts the wings. When the first set of muscles relaxes and the second set contracts, the thorax is squeezed in the opposite direction, which extends the body vertically and moves the wings downward. The below figure demonstrates this movement with only the first set of muscles.

The movement of the wings and the halteres are mechanically coupled. Sane et al. (2015) demonstrated that in freshly killed flies, without any neural input, the movement of wings was still coupled with the movement of halteres. When a forcep was used to manually move a wing up and down, not only did the opposite wing move in synchrony, the halteres also beat in antiphase with both wings. The source of this coupling however, was not between the muscles which control the halteres and those that control the wings. Instead, two small ridges of cuticle known as the subepimeral ridges were found to be responsible. These ridges connect the right wing to the right haltere and the left wing to the left haltere.

Each side of the body must be synchronized and the two sides are also coupled. That is, the left and right wings and thus the left and right halteres always beat at the same frequency. However, the amplitude of the wingbeat does not always have to be the same on the left and right side. This is what allows the flies to turn and is accomplished using a gearbox, much like what you would find in an automobile. This gearbox can change the maximum amplitude of the wing movement and determine its speed of motion. The wings of flies even have a clutch structure at their base. The clutch moves between grooves in the gearbox, to engage and disengage the wing muscles and also modulate the wingbeat amplitude. When the amplitude of the left wing is less than the right, the fly will make a left turn. Even though haltere movement is controlled by separate muscles than the wings, because the wings are mechanically coupled with the halteres, changes in wingbeat frequency extend to the haltere-beat frequency as well, but haltere beat amplitude does not change.

Although halteres are coupled with the wings and with each other during flight, some flies oscillate their halteres while walking (without oscillating their wings). Because the haltere muscles are tiny in comparison to the flight muscles, flight muscle activity completely overshadows that of the haltere muscles during flight. It is unknown how haltere muscle activity during flight differs from walking. The left and right halteres show much more variable phase relationships while walking compared with flying, which may indicate decoupling of the left and right haltere muscles.

Differences between species
Although halteres are always synchronized with the movements of the wings, the phase at which they oscillate differs between species. Brachyceran flies (short-antennaed) oscillate their halteres almost exactly opposite their wings (180 degrees). More ancient suborders such as the Nematecerans (long-antennaed flies), which for example include crane flies and mosquitoes, exhibit a variety of wing-haltere phasing. These observed differences in wing-haltere coordination suggest that differences in sensory neuron output also exist between species. This means that the decoding mechanisms used by the central nervous system to interpret such movements and produce adequate motor output probably also vary depending on phylogeny.

Morphology

The general structure of halteres are well recognized, but much variability exists between species. The more ancient family groups, such as Tipuloidea (crane flies), possess halteres with rather long stalks. This causes the haltere bulbs to be much further from the body and easily visible to the naked eye. More derived families, such as Calliphoridae (blow flies), have developed specialized structures called "calyptrae" or "squama", which are tiny flaps of wing, that cover the haltere. Pringle (1948) hypothesized that they prevented wind turbulence from affecting haltere movements, allowing more precise detection of body position, but this was never tested. The stalk of the haltere is also not always straight. Instead, the stalk's shape in more derived families tends to be reflective of the body shape of the individual. This minimizes the amount of air space between end-knobs and the sides of the abdomen and thorax. In these families, the halteres beat so close to the body that the distance between haltere and thorax is a fraction of the diameter of the haltere bulb. An extreme example of this trait is in the family Syrphidae (hoverflies), where the bulb of the haltere is positioned nearly perpendicular to the stalk.

Flies typically hold their halteres at a 90-degree offset. To visualize this, if you were to imagine a person holding their arms out sideways, this would be a 180-degree offset. If that person then moved their arms backward so that the angle created between their fingertips and spine was 90 degrees, this would be a 90-degree offset. The halteres of flies work the same way. They are positioned behind their bodies, forming a 90-degree angle between the haltere bulbs and the center of their thorax. It is necessary for the halteres to be positioned like this in order to detect the three axes of motion. Those axes are yaw, pitch and roll, as illustrated in the above figure (Directions of rotation). The mechanoreceptors at the base of the halteres are only able to measure force in two directions (horizontal and vertical), so a single haltere is only able to measure rotations along two of the three axes. Because the halteres are set at different angles (90-degree offset), they also beat along two separate horizontal and vertical axes. This gives them the ability to acquire information from two non-parallel planes and allows sensation of rotation in all three directions. However, flies are most sensitive to pitch.

Neurophysiology
When halteres are experimentally induced to flap, volleys of action potentials within the haltere nerve occur in synchrony with the haltere-beat frequency. When flies are then rotated, these volleys break down, likely in response to different groups of sensilla being activated to inform the fly of its recently changed body position. Haltere afferents have also been shown to terminate in the mesothoracic neuropil where flight muscle neurons are located. Haltere afferent activity responding to rotations and wing steering behavior converge in this processing region.

The haltere nerve
Sensory inputs from five sensory fields located at the base of the haltere all converge onto one nerve, the haltere nerve. How these sensory fields are organized at the level of the central nervous system is currently unknown. It has been determined that those five sensory fields all project to the thorax in a "region-specific" way and afferents originating from the forewing were also shown to converge in the same regions. Not every specific target for the haltere afferents have been determined, but a few connections between motor neurons known to be involved in wing steering control and particular haltere sensory fields have been identified, particularly one synapse between the haltere nerve and a wing steering motor neuron known as mnb1.

Muscles
Flies use indirect flight muscles to accomplish wing movement, and the beating haltere movements are driven by the same group of muscles (see dynamics section). In addition to the indirect flight muscles which are responsible for the flapping motion, there are also steering muscle which control the rotation/angle of the wings. Because halteres evolved from hindwings, the same complement of steering muscles exists for the other directions of movement as well. Chan et al. (1998) identified 10 direct control muscles in the haltere similar to those found in the forewing. In 1998, Chan and Dickinson proposed that the planned haltere movements (without external forces acting on them) were what initiated planned turns. To explain this, imagine a fly that wishes to turn to the right. Unfortunately, as soon as it does, the halteres sense a body rotation and reflexively correct the turn, preventing the fly from changing direction. Chan and Dickinson (1998) suggested that what the fly does to prevent this from occurring is to first move its halteres as if it were being pushed in the opposite direction that it wants to go. The fly has not moved, but the halteres have sensed a perturbation. This would allow the haltere-initiated reflex to occur, correcting the imagined perturbation. The fly would then be able to execute its turn in the desired direction. This is not how flies actually turn. Mureli and Fox (2015) showed that flies are still capable of performing planned turns even when their halteres have been removed entirely.

Campaniform sensilla
The way in which rotation sensation is accomplished is that there are five distinct sensory fields located at the base of the haltere. These fields, which actually contain the majority of campaniform sensilla found on the exoskeleton of blowflies (more than 400 campaniform sensilla per haltere), are activated in response to strain created by movements at the haltere base in different directions (due to Coriolis forces acting on the end knobs). Campaniform sensilla are cap-shaped protrusions located on the surface of the exoskeleton (cuticle) of insects. Attached inside the cap is the tip of a dendritic projection (or sensory nerve fiber). The outer segment of the dendritic projection is attached to the inside surface of the cap. When the haltere is pushed to one side, the cuticle of the insect bends and the surface of the cap is distorted. The inner dendrite is able to detect this distortion and convert it to an electrical signal which is sent to the central nervous system to be interpreted.

Chordotonal organs
Chordotonal organs detect and transmit distortions in their position/shape in the same way that campaniform sensilla do. They differ slightly at their site of detection. Chordotonal organs, unlike campaniform sensilla, exist beneath the cuticle and typically respond to stretch as opposed to distortion or bending. Their sensory nerve endings attach between two internal points and when those points are stretched, the difference in length is what is detected and transformed into electrical signaling. There are far fewer chordotonal organs at the base of the haltere than campaniform sensilla (on the order of hundreds), so it is assumed that they are far less important for detecting and transmitting rotational information from haltere movements.

Head stabilization
Insect eyes are unable to move independently of the head. In order for flies to stabilize their visual fields, they must adjust the position of their entire head. Sensory inputs detected by halteres not only determine the position of the body, but also, the position of the head, which can move independently from the body. Halteres are particularly useful for detecting fast perturbations during flight and only respond to angular velocities (speeds of rotation) above a certain threshold. When flies are focused on an object in front of them and their body is rotated, they are able to maintain their head position so that the object remains focused and upright. Hengstenberg (1988) found that in the roll direction of rotation, the flies' ability to maintain their head position in response to body motion was only observed at speeds above 50 degrees per second and their ability peaked at 1500 degrees per second. When halteres were removed at the bulb (to retain intact sensory organs at the base) the fly's ability to perceive roll movements at high angular velocities disappeared.

Halteres and vision both play a role in stabilizing the head. Flies are also able to perform compensatory head movements to stabilize their vision without the use of their halteres. When the visual field is artificially rotated around a fly at slower angular velocities, head stabilization still occurs. Head stabilization outputs due to optical inputs alone are slower to respond, but also last longer than those due to haltere inputs. From this result it can be concluded that although halteres are required for detecting fast rotations, the visual system is adept by itself at sensing and correcting for slower body movements. Thus, the visual and mechanosensory (halteres) systems work together to stabilize the visual field of the animal: first, by quickly responding to fast changes (halteres), and second, by maintaining that response until it is corrected (vision).

Visual-motor integration
Flies rely on both visual information from their compound eyes and mechanical input from their halteres. Sherman and Dickinson (2002) discovered that the responsiveness of the halteres and eyes are tuned to complementary speeds of rotation. Responses to body rotations detected via the visual system are greatest at slow speeds and decrease with increased angular velocity. In contrast, body rotations detected by the halteres elicit the greatest responses at higher angular velocities and degrade as the speed of rotation decreases. The integration of these two separately tuned sensors allows the flies to detect a wide range of angular velocities in all three directions of rotation.

Two main aspects of the visual field have been used to study fly vision, figure and background. Figures are the objects that the fly is focused on and background represents everything else. When haltere bulbs are removed from tethered flying flies, they are still able to track moving figures, but they struggle to stabilize moving backgrounds. If a static figure is placed in the field of view of a fly, its ability to stabilize a moving background is restored. This indicates that although halteres are not required for motion vision processing, they do contribute to it in a context-dependent manner, even when the behavior is separated from body rotations. Context determines whether the fly will use its halteres or vision as the primary source of body/head position information.

Non-flying haltere activity
The necessity of halteres in flight has been well documented, yet little is known about their use in other behaviors such as walking. Certain flies in the families Muscidae, Anthomyiidae, Calliphoridae, Sarcophagidae, Tachinidae, and Micropezidae have been documented to oscillate their wings while walking in addition to during flight. The oscillation of the haltere is similar in amplitude and frequency during walking and flight for these flies, and the halteres always oscillate when walking or when flying. All other families of Diptera never oscillate their halteres while walking, but always do so while flying. Flesh flies are among those that oscillate their halteres while walking, and also perform more poorly at certain walking tasks when their halteres are removed. In contrast, fruit flies, which do not oscillate their halteres when walking, do not exhibit any differences in ability when their halteres are removed. This indicates that haltere inputs are behaviorally relevant to those species which oscillate them while walking and that they aid those individuals in walking behavior. Flies in the Calyptratae clade which include common flies like house flies, blow flies, and flesh flies also use their halteres during takeoff, whereas non-Calyptratae flies do not. Calyptratae flies are able to take off around five times faster than other flies. Calyptratae flies lacking halteres take a lot longer to become airborne, but takeoff time is not affected in non-Calyptratae flies without halteres. Stability during takeoff also suffers with haltere removal, but only in Calyptratae flies.

title: Halteres


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User:Paul~enwiki

Annoyingly, it seems I'm about to lose the ID I've had since 2000-something. Ah well. I'm still Paul. Just not here.

Here I am Paul~enwiki :-/

Paul
The mysterious vanishing Paul. I thought I'd put myself back in with the name under which I edited what seems like ages ago, but probably wasn't. Now there's a sentence crying out for an edit.

There is half-digested text about ftp and its secure cousins at the bottom of the page...

 * Somebody keeps requesting password resets for me - please stop it -Paul 11:02, 29 November 2005 (UTC)
 * It's getting ridiculous - twice this week, for instance. The latest request from 64.236.245.243. Pick your own user ID, please! - Paul 20:44, 19 January 2006 (UTC)
 * And again - go away, children, please!

OK. The following attempts (for as far back as I have records) - let's see if there is a pattern:
 * 202.156.6.54 at 2006-01-19 00:43 GMT (...cache.maxonline.com.sg)
 * 64.236.245.243 at 2006-01-19 11:52 (...gate.timeinc.com)
 * 66.215.196.168 at 2006-02-01 09:10 (...dhcp.ccmn.ca.charter.com)
 * 66.215.196.168 at 2006-02-01 09:11
 * 66.215.196.168 at 2006-02-01 09:11 - third time that day
 * 136.206.1.17 at 2006-02-01 12:33 (...proxy3.dcu.ie)
 * 69.195.15.84 at 2006-02-05 00:41 GMT (...cpe.net.cable.rogers.com)
 * 68.230.173.217 at 2006-02-08 14:46 (...nc.hr.cox.net)
 * 68.230.173.217 at 2006-02-08 14:51
 * 68.230.173.217 at 2006-02-08 15:00
 * 68.230.173.217 at 2006-02-08 15:00
 * 68.230.173.217 at 2006-02-08 15:01
 * 195.93.21.71 at 2006-02-08 21:25 (cache-los-ac07.proxy.aol.com)
 * 172.209.210.215 at 2006-02-09 21:23 (...ipt.aol.com)

Stuff wot I done wrote
What can I say. I edit stuff occasionally (often on computing, Ireland, gramer an speling). And I'm called Paul.

Some articles I've written or contributed significantly to include:
 * Belfast Agreement
 * Northern Ireland peace process - still needs work on later setions
 * Independent Commission on Policing for Northern Ireland
 * Independent International Commission on Decommissioning
 * Internet governance - added historical perspective on current model - not mostly about the UN any more :)
 * Internet protocol suite - clarifications of what goes where in the stack, and how some of the protocols interrelate. At least it was clearer to me, after I'd updated it! Fortunately other people have made it even clearer ;-)
 * Legal aspects of computing - a rambling (but slightly structured) list of articles and topics - my initial attempt to gather together some threads of where law and computing meet. More links and articles welcome :-)
 * EU Directive on the Patentability of Computer-Implemented Inventions - this one was a bit controversial...
 * Northern Ireland peace process - this still needs some work on events after the Assembly started.

There are probably more - maybe even on interesting topics - but I can't seem to think of any right now.

Random comments :-)
Well, hello vanishing Paul;-) -- WojPob

Hi, Woj! -- Paul >:<

I think I need to reference this RFC.

FTP and Secure variants
''Right now, this is just a set of notes for me... A disambiguation / introduction article might have less information than this. It might also have corrections.''

There is a maze of file transfer protocols - especially when you start to look at secure ones. It's complicated by the way many of them use identical or similar names.

 * 1) FTP - the venerable and insecure file transfer protocol, uses 2 connections on different ports (20 & 21)
 * 2) * RFC 959 (with later extensions)
 * 3) * active mode: client tells server which port it is listening on, server connects from port 20 & exchanges file
 * 4) * passive mode: client asks server to pick a port, client connects to that port on server (works better with NAT)
 * 5) SSH file transfer protocol (files exchanged using ssh on port 22)
 * 6) * no RFC for this. Most widely used versions v3 & v4 (v6 was documented in an expired internet draft)
 * 7) * this is PROBABLY the one you want, for transferring files securely
 * 8) * sftp (by OpenSSH) is one client for this protocol
 * 9) * not to be confused with FTP over SSH, sometimes called Secure FTP (rare)
 * 10) * Secure File Transfer Protocol sometimes refers to SSH file transfer protocol (& sometimes to FTP over SSH)
 * 11) * compare with scp (secure copy, which is a simpler file copy protocol also run over ssh)
 * 12) * end to end security => harder to proxy/control/log at network perimiter (man in the middle proxies exist)
 * 13) FTP with SSL/TLS, (aka ftp-ssl, or ftps, or ftp secure) ?
 * 14) * RFC 4217 (uses same security standards/certs as secure https web traffic - server needs a certificate)
 * 15) * firewall issue - cannot snoop packets to determine what ports to open for ftp data channel
 * 16) * implicit security - deprecated, uses tcp ports 989 & 990.
 * 17) * explicit security - through new ftp AUTH command in RFC 2228, same ports as normal ftp
 * 18) FTP over SSH
 * 19) * because FTP uses multiple connections, it it trickier to use over ssh.
 * 20) * needs intelligence in the file transfer client or in the ssh client to ensure both connections are encrypted
 * 21) Secure File Transfer Protocol (secure FTP) is a confusing term
 * 22) * sometimes it refers to SSH file transfer protocol (2, above - possibly due to the latter's "sftp" client)
 * 23) * sometimes it refers to FTP over SSH (3, above)
 * 24) Simple File Transfer Protocol (rarely used)
 * 25) * RFC 913: uses port 115, ancient
 * 26) * this is a silly protocol. Don't go there.
 * 27) TFTP - Trivial FTP (insecure, simple, sometimes used for booting over network)
 * 28) * RFC 1350: via UDP
 * 29) * not useful for generalised file transfer

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: User:Paul~enwiki


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Halley's Comet

Halley's Comet is the only known short-period comet that is consistently visible to the naked eye from Earth, appearing every 72–80 years. It last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. Officially designated 1P/Halley, it is also commonly called Comet Halley, or sometimes simply Halley.

Halley's periodic returns to the inner Solar System have been observed and recorded by astronomers around the world since at least 240 BC, but it was not until 1705 that the English astronomer Edmond Halley understood that these appearances were re-appearances of the same comet. As a result of this discovery, the comet is named after Halley.

During its 1986 visit to the inner Solar System, Halley's Comet became the first comet to be observed in detail by spacecraft, providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation. These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipple's "dirty snowball" model, which correctly predicted that Halley would be composed of a mixture of volatile ices—such as water, carbon dioxide, ammonia—and dust. The missions also provided data that substantially reformed and reconfigured these ideas; for instance, it is now understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy.

Pronunciation
Comet Halley is usually pronounced, rhyming with valley, or sometimes , rhyming with daily. As to the surname Halley, Colin Ronan, one of Edmond Halley's biographers, preferred, rhyming with crawly. Spellings of Halley's name during his lifetime included Hailey, Haley, Hayley, Halley, Hawley, and Hawly, so its contemporary pronunciation is uncertain, but the version rhyming with valley seems to be preferred by current bearers of the surname.

Computation of orbit
Halley was the first comet to be recognised as periodic. Until the Renaissance, the philosophical consensus on the nature of comets, promoted by Aristotle, was that they were disturbances in Earth's atmosphere. This idea was disproven in 1577 by Tycho Brahe, who used parallax measurements to show that comets must lie beyond the Moon. Many were still unconvinced that comets orbited the Sun, and assumed instead that they must follow straight paths through the Solar System. In 1687, Sir Isaac Newton published his Philosophiæ Naturalis Principia Mathematica, in which he outlined his laws of gravity and motion. His work on comets was decidedly incomplete. Although he had suspected that two comets that had appeared in succession in 1680 and 1681 were the same comet before and after passing behind the Sun (he was later found to be correct; see Newton's Comet), he was initially unable to completely reconcile comets into his model.

Ultimately, it was Newton's friend, editor and publisher, Edmond Halley, who, in his 1705 Synopsis of the Astronomy of Comets, used Newton's new laws to calculate the gravitational effects of Jupiter and Saturn on cometary orbits. Having compiled a list of 24 comet observations, he calculated that the orbital elements of a second comet that had appeared in 1682 were nearly the same as those of two comets that had appeared in 1531 (observed by Petrus Apianus) and 1607 (observed by Johannes Kepler). Halley thus concluded that all three comets were, in fact, the same object returning about every 76 years, a period that has since been found to vary between 72 and 80 years. After a rough estimate of the perturbations the comet would sustain from the gravitational attraction of the planets, he predicted its return for 1758. While he had personally observed the comet around perihelion in September 1682, Halley died in 1742 before he could observe its predicted return.

Halley's prediction of the comet's return proved to be correct, although it was not seen until 25 December 1758, by Johann Georg Palitzsch, a German farmer and amateur astronomer. It did not pass through its perihelion until 13 March 1759, the attraction of Jupiter and Saturn having caused a retardation of 618 days. This effect was computed before its return (with a one-month error to 13 April) by a team of three French mathematicians, Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute. The confirmation of the comet's return was the first time anything other than planets had been shown to orbit the Sun. It was also one of the earliest successful tests of Newtonian physics, and a clear demonstration of its explanatory power. The comet was first named in Halley's honour by French astronomer Nicolas-Louis de Lacaille in 1759.

Some scholars have proposed that first-century Mesopotamian astronomers already had recognised Halley's Comet as periodic. This theory notes a passage in the Babylonian Talmud, tractate Horayot that refers to "a star which appears once in seventy years that makes the captains of the ships err". Others doubt this idea based on historical considerations about the exact timing of this alleged observation, and suggest it refers to other astronomical phenomena.

Researchers in 1981 attempting to calculate the past orbits of Halley by numerical integration starting from accurate observations in the seventeenth and eighteenth centuries could not produce accurate results further back than 837 owing to a close approach to Earth in that year. It was necessary to use ancient Chinese comet observations to constrain their calculations.

Orbit and origin
Halley's orbital period has varied between 74 and 80 years since 240 BC. Its orbit around the Sun is highly elliptical, with an orbital eccentricity of 0.967 (with 0 being a circle and 1 being a parabolic trajectory). The perihelion, the point in the comet's orbit when it is nearest the Sun, is 0.59 au. This is between the orbits of Mercury and Venus. Its aphelion, or farthest distance from the Sun, is 35 au, roughly the orbital distance of Pluto. Unlike the overwhelming majority of objects in the Solar System, Halley's orbit is retrograde; it orbits the Sun in the opposite direction to the planets, or, clockwise from above the Sun's north pole. The orbit is inclined by 18° to the ecliptic, with much of it lying south of the ecliptic. (Because it is retrograde, the true inclination is 162°.) Owing to the retrograde orbit, it has one of the highest velocities relative to the Earth of any object in the Solar System. The 1910 passage was at a relative velocity of 70.56 km/s. Because its orbit comes close to Earth's in two places, Halley is associated with two meteor showers: the Eta Aquariids in early May, and the Orionids in late October.

Halley is classified as a periodic or short-period comet: one with an orbit lasting 200 years or less. This contrasts it with long-period comets, whose orbits last for thousands of years. Periodic comets have an average inclination to the ecliptic of only ten degrees, and an orbital period of just 6.5 years, so Halley's orbit is atypical. Most short-period comets (those with orbital periods shorter than 20 years and inclinations of 20–30 degrees or less) are called Jupiter-family comets. Those resembling Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets. , 105 Halley-type comets have been observed, compared with 816 identified Jupiter-family comets.

The orbits of the Halley-type comets suggest that they were originally long-period comets whose orbits were perturbed by the gravity of the giant planets and directed into the inner Solar System. If Halley was once a long-period comet, it is likely to have originated in the Oort cloud, a sphere of cometary bodies around 20,000–50,000 au from the Sun. Conversely the Jupiter-family comets are generally believed to originate in the Kuiper belt, a flat disc of icy debris between 30 au (Neptune's orbit) and 50 au from the Sun (in the scattered disc). Another point of origin for the Halley-type comets was proposed in 2008, when a trans-Neptunian object with a retrograde orbit similar to Halley's was discovered,, whose orbit takes it from just outside that of Uranus to twice the distance of Pluto. It may be a member of a new population of small Solar System bodies that serves as the source of Halley-type comets.

Halley has probably been in its current orbit for 16,000–200,000 years, although it is not possible to numerically integrate its orbit for more than a few tens of apparitions, and close approaches before 837 AD can only be verified from recorded observations. The non-gravitational effects can be crucial; as Halley approaches the Sun, it expels jets of sublimating gas from its surface, which knock it very slightly off its orbital path. These orbital changes cause delays in its perihelion passage of four days on average.

In 1989, Boris Chirikov and Vitold Vecheslavov performed an analysis of 46 apparitions of Halley's Comet taken from historical records and computer simulations. These studies showed that its dynamics were chaotic and unpredictable on long timescales. Halley's projected dynamical lifetime is estimated to be about 10 million years. The dynamics of its orbit can be approximately described by a two-dimensional symplectic map, known as the Kepler map, a solution to the restricted three-body problem for highly eccentric orbits. Based on records from the 1910 apparition, David Hughes calculated in 1985 that Halley's nucleus has been reduced in mass by 80 to 90% over the last 2,000 to 3,000 revolutions, and that it will most likely disappear completely after another 2,300 perihelion passages. More recent work suggests that Halley will evaporate, or split in two, within the next few tens of thousands of years, or will be ejected from the Solar System within a few hundred thousand years.

Structure and composition
The Giotto and Vega missions gave planetary scientists their first view of Halley's surface and structure. The nucleus is a conglomerate of ices and dust, often referred to as a "dirty snowball". Like all comets, as Halley nears the Sun, its volatile compounds (those with low boiling points, such as water, carbon monoxide, carbon dioxide and other ices) begin to sublimate from the surface. This causes the comet to develop a coma, or atmosphere, at distances up to 230000 km from the nucleus. Sublimation of this dirty ice releases dust particles, which travel with the gas away from the nucleus. Gas molecules in the coma absorb solar light and then re-radiate it at different wavelengths, a phenomenon known as fluorescence, whereas dust particles scatter the solar light. Both processes are responsible for making the coma visible. As a fraction of the gas molecules in the coma are ionised by the solar ultraviolet radiation, pressure from the solar wind, a stream of charged particles emitted by the Sun, pulls the coma's ions out into a long tail, which may extend more than 100 million kilometres into space. Changes in the flow of the solar wind can cause disconnection events, in which the tail completely breaks off from the nucleus.

Despite the vast size of its coma, Halley's nucleus is relatively small: barely 15 km long, 8 km wide and perhaps 8 km thick. Based on a reanalysis of images taken by the Giotto and Vega spacecraft, Lamy et al. determined an effective diameter of 11 km. Its shape has been variously compared to that of a peanut, a potato, or an avocado. Its mass is roughly 2.2$14.42 km$ kg, with an average density of about 0.55 g/cm3. The low density indicates that it is made of a large number of small pieces, held together very loosely, forming a structure known as a rubble pile. Ground-based observations of coma brightness suggested that Halley's rotation period was about 7.4 days. Images taken by the various spacecraft, along with observations of the jets and shell, suggested a period of 52 hours. Given the irregular shape of the nucleus, Halley's rotation is likely to be complex. The flyby images revealed an extremely varied topography, with hills, mountains, ridges, depressions, and at least one crater.

Halley is the most active of all the periodic comets, with others, such as Comet Encke and Comet Holmes, being one or two orders of magnitude less active. Its day side (the side facing the Sun) is far more active than the night side. Spacecraft observations showed that the gases ejected from the nucleus were 80% water vapour, 17% carbon monoxide and 3–4% carbon dioxide, with traces of hydrocarbons although more recent sources give a value of 10% for carbon monoxide and also include traces of methane and ammonia. The dust particles were found to be primarily a mixture of carbon–hydrogen–oxygen–nitrogen (CHON) compounds common in the outer Solar System, and silicates, such as are found in terrestrial rocks. The dust particles ranged in size down to the limits of detection (≈0.001 μm). The ratio of deuterium to hydrogen in the water released by Halley was initially thought to be similar to that found in Earth's ocean water, suggesting that Halley-type comets may have delivered water to Earth in the distant past. Subsequent observations showed Halley's deuterium ratio to be far higher than that found in Earth's oceans, making such comets unlikely sources for Earth's water.

Giotto provided the first evidence in support of Fred Whipple's "dirty snowball" hypothesis for comet construction; Whipple postulated that comets are icy objects warmed by the Sun as they approach the inner Solar System, causing ices on their surfaces to sublime (change directly from a solid to a gas), and jets of volatile material to burst outward, creating the coma. Giotto showed that this model was broadly correct, though with modifications. Halley's albedo, for instance, is about 4%, meaning that it reflects only 4% of the sunlight hitting it – about what one would expect for coal. Thus, despite astronomers predicting that Halley would have an albedo of about 0.17 (roughly equivalent to bare soil), Halley's Comet is in fact pitch black. The "dirty ices" on the surface sublime at temperatures between 170 K in sections of higher albedo to 220 K at low albedo; Vega 1 found Halley's surface temperature to be in the range 300 –. This suggested that only 10% of Halley's surface was active, and that large portions of it were coated in a layer of dark dust that retained heat. Together, these observations suggested that Halley was in fact predominantly composed of non-volatile materials, and thus more closely resembled a "snowy dirtball" than a "dirty snowball".

Before 1066
The first certain appearance of Halley's Comet in the historical record is a description from 240 BC, in the Chinese chronicle Records of the Grand Historian or Shiji, which describes a comet that appeared in the east and moved north. The only surviving record of the 164 BC apparition is found on two fragmentary Babylonian tablets, which were rediscovered in August 1984 in the collection of the British Museum.

The apparition of 87 BC was recorded in Babylonian tablets which state that the comet was seen "day beyond day" for a month. This appearance may be recalled in the representation of Tigranes the Great, an Armenian king who is depicted on coins with a crown that features, according to Vahe Gurzadyan and R. Vardanyan, "a star with a curved tail [that] may represent the passage of Halley's Comet in 87 BC." Gurzadyan and Vardanyan argue that "Tigranes could have seen Halley's Comet when it passed closest to the Sun on August 6 in 87 BC" as the comet would have been a "most recordable event"; for ancient Armenians it could have heralded the New Era of the brilliant King of Kings.

The apparition of 12 BC was recorded in the Book of Han by Chinese astronomers of the Han dynasty who tracked it from August through October. It passed within 0.16 au of Earth. According to the Roman historian Cassius Dio, a comet appeared suspended over Rome for several days portending the death of Marcus Vipsanius Agrippa in that year. Halley's appearance in 12 BC, only a few years distant from the conventionally assigned date of the birth of Jesus Christ, has led some theologians and astronomers to suggest that it might explain the biblical story of the Star of Bethlehem. There are other explanations for the phenomenon, such as planetary conjunctions, and there are also records of other comets that appeared closer to the date of Jesus's birth.

If Yehoshua ben Hananiah's reference to "a star which arises once in seventy years and misleads the sailors" refers to Halley's Comet, he can only have witnessed the 66 AD appearance. Another possible report comes from Jewish historian Josephus, who wrote that in 66 AD "The signs ... were so evident, and did so plainly foretell their future desolation ... there was a star resembling a sword, which stood over the city, and a comet, that continued a whole year". This portent was in reference to the city of Jerusalem and the First Jewish–Roman War.

The 141 AD apparition was recorded in Chinese chronicles.

The 374 AD and 607 approaches each came within 0.09 au of Earth. The 451 AD apparition was said to herald the defeat of Attila the Hun at the Battle of Chalons.

The 684 AD apparition was reported in Chinese records as the "broom star".

The 760 AD apparition was recorded in the Zuqnin Chronicle's entry for iyyōr 1071 SE (May 760 AD), calling it a "white sign":

"The year [SE] one thousand seventy one (AD 759/760). In the month of iyyōr (May) a white sign was seen in the sky, before early twilight, in the north-east [quarter], in the Zodiac [sign] which is called Aries, to the north from these three stars in it, which are very shining. And it resembled in its shape a broom [...] And the sign itself remained for fifteen nights, until dawn of the feast of Pentecost."

In 837 AD, Halley's Comet may have passed as close as 0.03 AU from Earth, by far its closest approach. Its tail may have stretched 60 degrees across the sky. It was recorded by astronomers in China, Japan, Germany, the Byzantine Empire, and the Middle East; Emperor Louis the Pious observed this appearance and devoted himself to prayer and penance, fearing that "by this token a change in the realm and the death of a prince are made known".

In 912 AD, Halley is recorded in the Annals of Ulster, which states "A dark and rainy year. A comet appeared."

1066
In 1066, the comet was seen in England and thought to be an omen: later that year Harold II of England died at the Battle of Hastings and William the Conqueror claimed the throne. The comet is represented on the Bayeux Tapestry and described in the tituli as a star. Surviving accounts from the period describe it as appearing to be four times the size of Venus, and shining with a light equal to a quarter of that of the Moon. Halley came within 0.10 au of Earth at that time.

This appearance of the comet is also noted in the Anglo-Saxon Chronicle. Eilmer of Malmesbury may have seen Halley in 989 and 1066, as recorded by William of Malmesbury:

"Not long after, a comet, portending (they say) a change in governments, appeared, trailing its long flaming hair through the empty sky: concerning which there was a fine saying of a monk of our monastery called Æthelmær. Crouching in terror at the sight of the gleaming star, 'You've come, have you?', he said. 'You've come, you source of tears to many mothers. It is long since I saw you; but as I see you now you are much more terrible, for I see you brandishing the downfall of my country.'"

The Irish Annals of the Four Masters recorded the comet as "A star [that] appeared on the seventh of the Calends of May, on Tuesday after Little Easter, than whose light the brilliance or light of The Moon was not greater; and it was visible to all in this manner till the end of four nights afterwards." Chaco Native Americans in New Mexico may have recorded the 1066 apparition in their petroglyphs.

The Italo-Byzantine chronicle of Lupus the Protospatharios mentions that a "comet-star" appeared in the sky in the year 1067 (the chronicle is erroneous, as the event occurred in 1066, and by Robert he means William).

"The Emperor Constantine Ducas died in the month of May, and his son Michael received the Empire. And in this year there appeared a comet star, and the Norman count Robert [sic] fought a battle with Harold, King of the English, and Robert was victorious and became king over the people of the English."

1145–1378

The 1145 apparition may have been recorded by the monk Eadwine.

According to legend, Genghis Khan was inspired to turn his conquests toward Europe by the westward-seeming trajectory of the 1222 apparition. In Korea, the comet was reportedly visible during the daylight on 9 September 1222.

The 1301 apparition was visually spectacular, and may be the first that resulted in convincing portraits of a particular comet. The Florentine chronicler Giovanni Villani wrote that the comet left "great trails of fumes behind", and that it remained visible from September 1301 until January 1302. It was seen by the artist Giotto di Bondone, who represented the Star of Bethlehem as a fire-coloured comet in the Nativity section of his Arena Chapel cycle, completed in 1305. Giotto's depiction includes details of the coma, a sweeping tail, and the central condensation. According to the art historian Roberta Olson, it is much more accurate than other contemporary descriptions, and was not equaled in painting until the 19th century. Olson's identification of Halley's Comet in Giotto's Adoration of the Magi is what inspired the European Space Agency to name their mission to the comet Giotto, after the artist.

Halley's 1378 appearance is recorded in the Annales Mediolanenses as well as in East Asian sources.

1456
In 1456, the year of Halley's next apparition, the Ottoman Empire invaded the Kingdom of Hungary, culminating in the siege of Belgrade in July of that year. In a papal bull, Pope Callixtus III ordered special prayers be said for the city's protection. In 1470, the humanist scholar Bartolomeo Platina wrote in his Lives of the Popes that,

"A hairy and fiery star having then made its appearance for several days, the mathematicians declared that there would follow grievous pestilence, dearth and some great calamity. Calixtus, to avert the wrath of God, ordered supplications that if evils were impending for the human race He would turn all upon the Turks, the enemies of the Christian name. He likewise ordered, to move God by continual entreaty, that notice should be given by the bells to call the faithful at midday to aid by their prayers those engaged in battle with the Turk."

Platina's account is not mentioned in official records. In the 18th century, a Frenchman further embellished the story, in anger at the Church, by claiming that the Pope had "excommunicated" the comet, though this story was most likely his own invention.

Halley's apparition of 1456 was also witnessed in Kashmir and depicted in great detail by Śrīvara, a Sanskrit poet and biographer to the Sultans of Kashmir. He read the apparition as a cometary portent of doom foreshadowing the imminent fall of Sultan Zayn al-Abidin (AD 1418/1420–1470).

After witnessing a bright light in the sky which most historians have identified as Halley's Comet, Zara Yaqob, Emperor of Ethiopia from 1434 to 1468, founded the city of Debre Berhan (tr. City of Light) and made it his capital for the remainder of his reign.

1531-1759

Petrus Apianus and Girolamo Fracastoro described the comet's visit in 1531, with the former even including graphics in his publication. Through his observations, Apianus was able to prove that a comet's tail always points away from the Sun.

In the Sikh scriptures of the Guru Granth Sahib, the founder of the faith Guru Nanak makes reference to "a long star that has risen" at Ang 1110, and it is believed by some Sikh scholars to be a reference to Halley's appearance in 1531.

Halley's periodic returns have been subject to scientific investigation since the 16th century. The three apparitions from 1531 to 1682 were noted by Edmond Halley, enabling him to predict it would return. One key breakthrough occurred when Halley talked with Newton about his ideas of the laws of motion. Newton also helped Halley get John Flamsteed's data on the 1682 apparition. By studying data on the 1531, 1607, and 1682 comets, he came to the conclusion these were the same comet, and presented his findings in 1696.

One difficulty was accounting for variations in the comet's orbital period, which was over a year longer between 1531 and 1607 than it was between 1607 and 1682. Newton had theorised that such delays were caused by the gravity of other comets, but Halley found that Jupiter and Saturn would cause the appropriate delays. In the decades that followed, more refined mathematics would be worked on, notable by Paris Observatory; the work on Halley also provided a boost to Newton and Kepler's rules for celestial motions. (See also .)

1835
At Markree Observatory in Ireland, Edward Joshua Cooper used a Cauchoix of Paris lens telescope with an aperture of 13.3 inch to sketch Halley's comet in 1835. The same apparition was sketched by German astronomer Friedrich Wilhelm Bessel. Observations of streams of vapour prompted Bessel to propose that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit.

An interview in 1910, of someone who was a teenager at the time of the 1835 apparition had this to say:

"When the comet was first seen, it appeared in the western sky, its head toward the north and tail towards the south, about horizontal and considerably above the horizon and quite a distance south of the Sun. It could be plainly seen directly after sunset every day, and was visible for a long time, perhaps a month ..."

They go on to describe the comet's tail as being more broad and not as long as the comet of 1843 they had also witnessed.

Famous astronomers across the world made observations starting August 1835, including Struve at Dorpat observatory, and Sir John Herschel, who made of observations from the Cape of Good Hope. In the United States telescopic observations were made from Yale College. The new observations helped confirm early appearances of this comet including its 1456 and 1378 apparitions.

At Yale College in Connecticut, the comet was first reported on 31 August 1835 by astronomers D. Olmstead and E. Loomis. In Canada reports were made from Newfoundland and also Quebec. Reports came in from all over by later 1835, and often reported in newspapers of this time in Canada.

Several accounts of the 1835 apparition were made by observers who survived until the 1910 return, where increased interest in the comet led to their being interviewed.

The time to Halley's return in 1910 would be only 74.42 years, one of the shortest known periods of its return, which is calculated to be as long as 79 years owing to the effects of the planets.

At Paris Observatory Halley's Comet 1835 apparition was observed with a Lerebours telescope of 24.4 cm aperture by the astronomer François Arago. Arago recorded polarimetric observations of Halley, and suggested that the tail might be sunlight reflecting off a sparsely distributed material; he had earlier made similar observations of Comet Tralles of 1819.

1910
The 1910 approach, which came into naked-eye view around 10 April and came to perihelion on 20 April, was notable for several reasons: it was the first approach of which photographs exist, and the first for which spectroscopic data were obtained. Furthermore, the comet made a relatively close approach of 0.15 au, making it a spectacular sight. Indeed, on 19 May, Earth actually passed through the tail of the comet. One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen, which led press to misquote the astronomer Camille Flammarion by stating he claimed that, when Earth passed through the tail, the gas "would impregnate the atmosphere and possibly snuff out all life on the planet". Despite reassurances from scientists that the gas would not inflict harm on Earth, the damage had already been done with members of the public panic buying gas masks and quack "anti-comet pills".

The comet added to the unrest in China on the eve of the Xinhai Revolution that would end the last dynasty in 1911. As James Hutson, a missionary in Sichuan Province at the time, recorded:

"The people believe that it indicates calamity such as war, fire, pestilence, and a change of dynasty. In some places on certain days the doors were unopened for half a day, no water was carried and many did not even drink water as it was rumoured that pestilential vapour was being poured down upon the earth from the comet."

The 1910 visitation is also recorded as being the travelling companion of Hedley Churchward, the first known English Muslim to make the Haj pilgrimage to Mecca. However, his explanation of its scientific predictability did not meet with favour in the Holy City.

The comet was used in an advertising campaign of Le Bon Marché, a well-known department store in Paris.

The comet was also fertile ground for hoaxes. One that reached major newspapers claimed that the Sacred Followers, a supposed Oklahoma religious group, attempted to sacrifice a virgin to ward off the impending disaster, but were stopped by the police.

American satirist and writer Mark Twain was born on 30 November 1835, exactly two weeks after the comet's perihelion. In his autobiography, published in 1909, he said,

"I came in with Halley's comet in 1835. It is coming again next year, and I expect to go out with it. It will be the greatest disappointment of my life if I don't go out with Halley's comet. The Almighty has said, no doubt: 'Now here are these two unaccountable freaks; they came in together, they must go out together.'"

Twain died on 21 April 1910, the day following the comet's subsequent perihelion. The 1985 fantasy film The Adventures of Mark Twain was inspired by the quotation.

Halley's 1910 apparition is distinct from the Great Daylight Comet of 1910, which surpassed Halley in brilliance and was visible in broad daylight for a short period, approximately four months before Halley made its appearance.

1986
The 1986 apparition of Halley's Comet was the least favourable on record. In February 1986, the comet and the Earth were on opposite sides of the Sun, creating the worst possible viewing circumstances for Earth observers during the previous 2,000 years. Halley's closest approach was 0.42 au. Additionally, increased light pollution from urbanization caused many people to fail in attempts to see the comet. With the help of binoculars, observation from areas outside cities was more successful. Further, the comet appeared brightest when it was almost invisible from the northern hemisphere in March and April 1986, with best opportunities occurring when the comet could be sighted close to the horizon at dawn and dusk, if not obscured by clouds.

The approach of the comet was first detected by astronomers David C. Jewitt and G. Edward Danielson on 16 October 1982 using the 5.1 m Hale Telescope at Mount Palomar and a CCD camera.

The first visual observation of the comet on its 1986 return was by an amateur astronomer, Stephen James O'Meara, on 24 January 1985. O'Meara used a home-built 24 in telescope on top of Mauna Kea to detect the magnitude 19.6 comet. The first to observe Halley's Comet with the naked eye during its 1986 apparition were Stephen Edberg (then serving as the coordinator for amateur observations at the NASA Jet Propulsion Laboratory) and Charles Morris on 8 November 1985.

The 1986 apparition gave scientists the opportunity to study the comet closely, and several probes were launched to do so. The Soviet Vega 1 probe began returning images of Halley on 4 March 1986, captured the first-ever image of its nucleus, and made its flyby on 6 March. It was followed by the Vega 2 probe, making its flyby on 9 March. On 14 March, the Giotto space probe, launched by the European Space Agency, made the closest pass of the comet's nucleus. There also were two Japanese probes, Suisei and Sakigake. Unofficially, the numerous probes became known as the Halley Armada.

Based on data retrieved by the largest ultraviolet space telescope of the time, Astron, in December 1985, a group of Soviet scientists developed a model of the comet's coma. The comet also was observed from space by the International Cometary Explorer (ICE). Originally launched as the International Sun-Earth Explorer 3, the spacecraft was renamed, and departed the Sun-Earth Lagrangian point in 1982 in order to intercept the comets 21P/Giacobini-Zinner and Halley. ICE flew through the tail of Halley's Comet, coming within about 40.2 e6km of the nucleus on 28 March 1986.

Two U.S. Space Shuttle missions—STS-51-L and STS-61-E—had been scheduled to observe Halley's Comet from low Earth orbit. The STS-51-L mission carried the Shuttle-Pointed Tool for Astronomy (Spartan Halley) satellite, also called the Halley's Comet Experiment Deployable (HCED). The mission to capture the ultraviolet spectrum of the comet ended in disaster when the Space Shuttle Challenger exploded in flight, killing all seven astronauts onboard. Scheduled for March 1986, STS-61-E was a Columbia mission carrying the ASTRO-1 platform to study the comet, but the mission was cancelled following the Challenger disaster and ASTRO-1 would not fly until late 1990 on STS-35.

After 1986

On 12 February 1991, at a distance of 14.3 au from the Sun, Halley displayed an outburst that lasted for several months. The comet released dust with a total mass of about 108 kg, which spread into an elongated cloud roughly 374,000 km by 269,000 km in size. The outburst likely started in December 1990, and then the comet brightened from about magnitude 25 to magnitude 19. Comets rarely show outburst activity at distances beyond 5 au from the Sun. Different mechanisms have been proposed for the outburst, ranging from interaction with the solar wind to a collision with an undiscovered asteroid. The most likely explanation is a combination of two effects, the polymerization of hydrogen cyanide and a phase transition of amorphous water ice, which raised the temperature of the nucleus enough for some of the more volatile compounds on its surface to sublime.

Halley was most recently observed in 2003 by three of the Very Large Telescopes at Paranal, Chile, when Halley's magnitude was 28.2. The telescopes observed Halley, at the faintest and farthest any comet had ever been imaged, in order to verify a method for finding very faint trans-Neptunian objects. Astronomers are now able to observe the comet at any point in its orbit.

On 9 December 2023, Halley's Comet reached the farthest and slowest point in its orbit from the Sun when it was travelling at 0.91 km/s with respect to the Sun.

2061
The next perihelion of Halley's Comet is predicted for 28 July 2061, when it will be better positioned for observation than during the 1985–1986 apparition, as it will be on the same side of the Sun as Earth. The closest approach to Earth will be one day after perihelion. It is expected to have an apparent magnitude of −0.3, compared with only +2.1 for the 1986 apparition. On 9 September 2060, Halley will pass within 0.98 au of Jupiter, and then on 20 August 2061 will pass within 0.0543 au of Venus.

2134
Halley will come to perihelion on 27 March 2134. Then on 7 May 2134, Halley will pass within 0.092 au of Earth. Its apparent magnitude is expected to be −2.0.

Apparitions
Halley's calculations enabled the comet's earlier appearances to be found in the historical record. The following table sets out the astronomical designations for every apparition of Halley's Comet from 240 BC, the earliest documented widespread sighting.

In the designations, "1P/" refers to Halley's Comet; the first periodic comet discovered. The number represents the year, with negatives representing BC. The letter-number combination indicates which it was of the comets observed for a given segment of the year, divided into 24 equal parts. The Roman numeral indicates which comet past perihelion it was for a given year, while the lower-case letter indicates which comet it was for a given year overall. The perihelion dates farther from the present are approximate, mainly because of uncertainties in the modelling of non-gravitational effects. Perihelion dates of 1531 and earlier are in the Julian calendar, while perihelion dates 1607 and after are in the Gregorian calendar. The perihelion dates for some of the early apparitions (particularly before 837 AD) are uncertain by a couple of days. While Halley's Comet usually peaks at around 0th magnitude, there are indications that the comet got considerably brighter than that in the past.

title: Halley's Comet


text:
MOPE

MOPE may refer to:

 * Ministry of Population and Environment, a government ministry in Nepal.
 * Ministry of Power and Energy, a government ministry in Sri Lanka.
 * Mope, a song by the Bloodhound Gang.
 * Mormon Pope, a slang term for the president of the Church of Jesus Christ of Latter-day Saints.
 * Ministry of Public Education
 * Ministry of Petroleum and Energy, a government ministry in Norway
 * "Most oppressed people ever", an assertion about Irish history coined by Liam Kennedy in Unhappy the Land
 * Mope a 2019 film dramatizing the story of Stephen Clancy Hill.

title: MOPE


text:
Eared seal

An eared seal, otariid, or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera (another species became extinct in the 1950s) and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans, the southern Indian, and Atlantic Oceans. They are conspicuously absent in the north Atlantic.

The words "otariid" and "otary" come from the Greek otarion meaning "little ear", referring to the small but visible external ear flaps (pinnae), which distinguishes them from the phocids.

Evolution and taxonomy
Morphological and molecular evidence supports a monophyletic origin of pinnipeds, sharing a common ancestor with Musteloidea, though an earlier hypothesis suggested that Otаriidae are descended from a common ancestor most closely related to modern bears. Debate remains as to whether the phocids diverged from the otariids before or after the walrus.

Otariids arose in the Miocene (15–17 million years ago) in the North Pacific, diversifying rapidly into the Southern Hemisphere, where most species now live. The earliest known fossil otariid is Eotaria crypta from southern California, while the genus Callorhinus (northern fur seal) has the oldest fossil record of any living otariid, extending to the middle Pliocene. It probably arose from the extinct fur seal genus Thalassoleon.

Traditionally, otariids had been subdivided into the fur seal (Arctocephalinae) and sea lion (Otariinae) subfamilies, with the major distinction between them being the presence of a thick underfur layer in the former. Under this categorization, the fur seals comprised two genera: Callorhinus in the North Pacific with a single representative, the northern fur seal (C. ursinus), and eight species in the Southern Hemisphere under the genus Arctocephalus; while the sea lions comprise five species under five genera. Recent analyses of the genetic evidence suggests that Callorhinus ursinus is in fact more closely related to several sea lion species. Furthermore, many of the Otariinae appear to be more phylogenetically distinct than previously assumed; for example, the Japanese sea lion (Zalophus japonicus) is now considered a separate species, rather than a subspecies of the California sea lion (Zalophus californius).

In light of this evidence, the subfamily separation has been removed entirely and the family Otariidae has been organized into seven genera with 16 species and two subspecies. Nonetheless, because of morphological and behavioral similarities among the "fur seals" and "sea lions", these remain useful categories when discussing differences between groups of species. Compared to sea lions, fur seals are generally smaller, exhibit greater sexual dimorphism, eat smaller prey and go on longer foraging trips; and, of course, there is the contrast between the coarse short sea lion hair and the fur seal's fur.

Anatomy and appearance
Otariids have proportionately much larger foreflippers and pectoral muscles than phocids, and have the ability to turn their hind limbs forward and walk on all fours, making them far more maneuverable on land. They are generally considered to be less adapted to an aquatic lifestyle, since they breed primarily on land and haul out more frequently than true seals. However, they can attain higher bursts of speed and have greater maneuverability in the water. Their swimming power derives from the use of flippers more so than the sinuous whole-body movements typical of phocids and walruses.

Otariids are further distinguished by a more dog-like head, sharp, well-developed canines, and the aforementioned visible external pinnae. Their postcanine teeth are generally simple and conical in shape. The dental formula for eared seals is:. Sea lions are covered with coarse guard hairs, while fur seals have a thick underfur, which has historically made them the objects of commercial exploitation.

Male otariids range in size from the 70 kg Galápagos fur seal, smallest of all otariids, to the over 1,000-kg (2,200-lb) Steller sea lion. Mature male otariids weigh two to six times as much as females, with proportionately larger heads, necks, and chests, making them the most sexually dimorphic of all mammals.

Behavior
All otariids breed on land during well-defined breeding seasons. Except for the Australian sea lion, which has an atypical 17.5 month breeding cycle, they form strictly annual aggregations on beaches or rocky substrates, often on islands. All species are polygynous; i.e. successful males breed with several females. In most species, males arrive at breeding sites first and establish and maintain territories through vocal and visual displays and occasional fighting. Females typically arrive on shore a day or so before giving birth. While considered social animals, no permanent hierarchies or statuses are established on the colonies. The extent to which males control females or territories varies between species. Thus, the northern fur seal and the South American sea lion tend to herd specific harem-associated females, occasionally injuring them, while the Steller sea lion and the New Zealand sea lion control spatial territories, but do not generally interfere with the movement of the females. Female New Zealand sea lions are the only otrariids that move up to 2 km into forests to protect their pups during the breeding season.

Otariids are carnivorous, feeding on fish, squid and krill. Sea lions tend to feed closer to shore in upwelling zones, feeding on larger fish, while the smaller fur seals tend to take longer, offshore foraging trips and can subsist on large numbers of smaller prey items. They are visual feeders. Some females are capable of dives of up to 400 m.

Species
Family Otariidae
 * Subfamily Arctocephalinae (fur seals)
 * Genus Arctocephalus
 * Brown fur seal, A. pusillus
 * South African fur seal, A. pusillus pusillus
 * Australian fur seal, A. pusillus doriferus
 * Antarctic fur seal, A. gazella
 * Guadalupe fur seal, A. townsendi
 * Juan Fernández fur seal, A. philippii
 * Galápagos fur seal, A. galapagoensis
 * New Zealand fur seal (or southern fur seal), A. forsteri
 * Subantarctic fur seal, A. tropicalis
 * South American fur seal, A. australis
 * Genus Callorhinus
 * Northern fur seal, C. ursinus
 * Subfamily Otariinae (sea lions)
 * Genus Eumetopias
 * Steller sea lion, E. jubatus
 * Genus Neophoca
 * Australian sea lion, N. cinerea
 * Genus Otaria
 * South American sea lion, O. flavescens
 * Genus Phocarctos
 * New Zealand sea lion (or Hooker's sea lion), P. hookeri
 * Genus Zalophus
 * California sea lion, Z. californianus
 * †Japanese sea lion, Z. japonicus – extinct (1970s)
 * Galápagos sea lion, Z. wollebaeki

Although the two subfamilies of otariids, the Otariinae (sea lions) and Arctocephalinae (fur seals), are still widely used, recent molecular studies have demonstrated that they may be invalid. Instead, they suggest three clades within the family; one consisting of the northern sea lions (Eumetopias and Zalophus), one of the northern fur seal (Callorhinus) and its extinct relatives, and the third of all the remaining Southern Hemisphere species.

title: Eared seal


text:
Pardubice

Pardubice (Pardubitz) is a city in the Czech Republic. It has about 92,000 inhabitants. It is the capital city of the Pardubice Region and lies on the Elbe River. The historic centre is well preserved and is protected as an urban monument reservation.

Pardubice is known as the centre of industry, which represents an oil refinery or an electronic equipment plant. The city is well known for its sport events, which include the Velká pardubická steeplechase in horse racing, the Golden Helmet of Pardubice in motorcycle racing, and the Czech Open international chess and games festival.

Administrative division
Pardubice is divided into eight boroughs, which are further divided into 27 administrative parts (in brackets):
 * Pardubice I (Bílé Předměstí (partly), Pardubice-Staré Město, Zámek, Zelené Předměstí (partly));
 * Pardubice II (Cihelna, Polabiny, Rosice (partly));
 * Pardubice III (Bílé Předměstí (partly), Studánka (partly));
 * Pardubice IV (Bílé Předměstí (partly), Černá za Bory, Drozdice, Mnětice, Nemošice, Pardubičky, Staročernsko, Studánka (partly), Žižín);
 * Pardubice V (Dražkovice, Nové Jesenčany, Zelené Předměstí (partly));
 * Pardubice VI (Lány na Důlku, Opočínek, Popkovice, Staré Čívice, Svítkov, Zelené Předměstí (partly));
 * Pardubice VII (Doubravice, Ohrazenice, Rosice (partly), Semtín, Trnová);
 * Pardubice VIII (Hostovice).

Etymology
The name Pardubice is derived from the personal Polish name Porydęb. It was the name of the leader of the monks who came here from Poland. For the first time the name was recorded in the form of Pordobice.

Geography
Pardubice is located about 90 km east of Prague. The city lies at the confluence of the Elbe and Chrudimka rivers. There are several fishponds, artificial lakes and oxbow lakes of the Elbe in the municipal territory.

Pardubice is located in the East Elbe Table, in the eastern part of the Polabí lowland. The highest point is the hill Stropinský vrch at 258 m above sea level, located on the southeastern municipal border.

History
The first written mention of Pardubice is from 1295, when Pope Boniface VIII took over the protection of the local Church of Saint Bartholomew with the order of Canons Regular of the Penitence of the Blessed Martyrs. In the first half of the 14th century, the settlement was acquired by a noble family, later known as Lords of Pardubice. In 1340, when Pardubice was inherited by Arnošt of Pardubice, it was first referred to as a city.

In 1491, Pardubice was bought by Vilém II of Pernštejn, who continued to expand the city and made significant impact on its prosperity. He chose Pardubice as the centre of his estate and began to build a city that corresponded to his status. The Pernštejn family had the entire historic centre with the Renaissance square built. They also had rebuilt the medieval castle into a comfortable fortified residence. In 1560, the Pernštejns were forced to sell the estate to Emperor Ferdinand I because of debts.

During the Thirty Years' War, the city was besieged by the army of General Lennart Torstensson, but was not conquered.

An important milestone in the history of the city was the year 1845, when the railway from Prague to Olomouc was finished. Pardubice became an important railway junction, which led to the development of the food, engineering and chemical industries, and subsequently the development of social and cultural life. In 1874, the Velká pardubická steeplechase horse race took place for the first time. In 1910, Jan Kašpar made here the first successful flight in Czech lands and a year later he made history by flying the first long-haul flight from Pardubice to Prague.

Until 1918, the city was part of Austria Hungary. The seat of the Pardubice district, it was one of the 94 Bezirkshauptmannschaften in Bohemia.

In the interwar period, Pardubice continued to develop until its heyday ended with the advent of World War II. During the war, the city was damaged by air strikes of the Allies, and the Fanto Werke refinery was repeatedly bombed during the oil campaign.

Economy
Pardubice is known as an industrial city. The dominant industries are chemical industry, electrical engineering and mechanical engineering. Tesla electronics manufacturer operated here in 1921–1989. In 2000, Foxconn established a production plant in its former premises. This electronics manufacturer is the largest employer in Pardubice.

Pardubice has a long tradition in the chemical industry. It is represented by the Paramo refinery, which was founded by David Fanto in 1889. Today it is owned by Orlen Unipetrol. In Pardubice-Semtín there are the companies Explosia (a manufacturer of explosives founded in 1920, which is associated with the invention of Semtex plastic explosive) and its subsidiary Synthesia (manufacturer of cellulose, pigments and dyes, and organic compounds, established in 1929).

For centuries, Pardubice is known for the production of gingerbread. The gingerbread guild was established in the 16th century. The first factory was founded in 1913. Since 2008, Pardubice gingerbread is a protected geographical indication by the European Union.

Transport
Pardubice is located at the crossroads of three main roads: The I/2, which connects Pardubice with Prague; the I/36 from Pardubice to Rychnov nad Kněžnou District; and the I/37, which connects Hradec Králové with Žďár nad Sázavou and the D1 motorway.

Pardubice main railway station is an important railway junction. Pardubice has direct railway connection with many cities, including Prague, Brno, Olomouc, Ostrava and Liberec in the Czech Republic, Bratislava, Žilina and Košice in Slovakia, Budapest in Hungary, and Vienna and Graz in Austria. The territory of Pardubice is served by eight train stations and stops.

Pardubice is served by Pardubice Airport, which is used as both military and civilian international airport.

Intra-city transport is provided by the company Dopravní podnik města Pardubic a.s., which is owned by the city of Pardubice. In addition to buses, trolleybuses also provide intra-city transport. Trolleybus service was started in 1952. There are 12 trolleybus lines in operation.

Education
Pardubice is home to University of Pardubice. It was founded in 1950 as Chemical College and is mainly focused on fields historically associated with the city, such as the chemical industry and transportation.

Sport
The city was first represented in the top national football competition by SK Pardubice in the 1930s and 1940s. Later VCHZ Pardubice played in the top national league in the 1968–69 season. Nowadays the city is represented by FK Pardubice, which plays in the Czech First League. Women's team plays in the Czech Women's First League.

The ice hockey club HC Dynamo Pardubice plays in the Czech Extraliga. The team plays its home games at Enteria arena.

The basketball team is BK JIP Pardubice, playing in the National Basketball League.

Pardubice is also represented in the Czech rink bandy league.

Pardubice hosts two world-famous sporting events each year. The Velká pardubická steeplechase was first held in 1874 and is one of the most famous horse races in Europe. The second event is the Golden Helmet of Pardubice, a motorcycle speedway competition held at the Svítkov Stadium. The Golden Helmet has been run since 1929 is one of the oldest individual titles in world speedway. AMK Zlatá Přilba Pardubice is a speedway team that race at the Svítkov Stadium.

The Czech Open international chess and games festival has been held in Pardubice since 1990. The city was also known for the Czech Open in golf, but it was last held in 2011.

Sights
The landmark and symbol of Pardubice is the Green Gate as a remnant of the city's fortifications. It is a Renaissance gate with a façade decorated by a relief designed by Mikoláš Aleš, which depicts the Lords of Pardubice. Behind the gate is a 60 m high tower that serves as an lookout tower. In its interior there is also an exposition with the history and legends of the city.

Pardubice Castle was built at the end of the 13th century and rebuilt in the Renaissance style at the turn of the 15th and 16th centuries. Massive fortifications are preserved around the castle. Today the castle houses the Museum of East Bohemia in Pardubice and Gallery of East Bohemia in Pardubice.

The original Church of Saint Bartholomew was built in 1295 and destroyed during the Hussite Wars. The today's Church of Saint Bartholomew was built together with a monastery in 1507–1514. It was used as a burial place of the Pernštejn family. In the interior there is a valuable main altar with the painting "The Passion of St. Bartholomew" from 1692 by Michael Willmann and a painting decoration by Mikoláš Aleš.

The Church of the Annunciation of the Virgin Mary was founded by Arnošt of Pardubice before 1359. Its present late Gothic and Renaissance appearance dates from the first half of the 16th century. Until 1786, the church belonged to a Minorite monastery, from which time there are extensive underground tombs under the church.

The House at Jonáš is one of the most treasured burgher houses in Pardubice. It was built after the fire that hit the city in 1507. It is known for its façade, decorated with a stucco relief from 1797, showing a biblical scene of a whale swallowing the prophet Jonah. The premises of the house are used by the Gallery of East Bohemia in Pardubice.

The Zámeček Memorial is a place of reverence that commemorates execution of 194 people in 1942. The place is a national cultural monument and at its centrepiece is a granite monument dating from 1949.

Notable people

 * Gustav Gärtner (1855–1937), pathologist
 * Božena Viková-Kunětická (1862–1934), politician, writer, and feminist
 * František Lexa (1876–1960), Egyptologist
 * Vilém Mathesius (1882–1945), linguist and writer
 * Jan Kašpar (1883–1927), aviator and aircraft constructor
 * Emil Artur Longen (1885–1936), playwright, actor and screenwriter
 * Oskar Brázda (1887–1977), painter
 * Emanuela Nohejlová-Prátová (1900–1995), numismatist; died here
 * Věra Vovsová (1912–1998), painter, lived here
 * Jan Tauc (1922–2010), Czech-American physicist
 * Petr Haničinec (1930–2007), actor
 * Jiří Gruša (1938–2011), poet, prose writer and translator
 * Vladimír Nadrchal (born 1938), ice hockey player
 * Alois Švehlík (born 1939), actor
 * Petr Kabeš (1941–2005), poet
 * Stanislav Prýl (1942–2015), ice hockey player
 * Jiří Crha (born 1950), ice hockey player
 * Otakar Janecký (born 1960), ice hockey player and coach
 * Hynek Kmoníček (born 1962), diplomat
 * Ivo Křen (1964–2020), graphic artist and glass art theoretician
 * Roman Prymula (born 1964), physician, epidemiologist and politician
 * Dominik Hašek (born 1965), ice hockey player
 * Edita Adlerová (born 1971), mezzo-soprano
 * Tereza Maxová (born 1971), model
 * Radek Baborák (born 1976), French horn player and conductor
 * Nora Fridrichová (born 1977), television presenter
 * Lukáš Wagenknecht (born 1978), economist and politician
 * Jan Bulis (born 1978), ice hockey player
 * Jiří Welsch (born 1980), basketball player
 * Michal Meduna (born 1981), footballer
 * Aleš Hemský (born 1983), ice hockey player
 * Filip Bandžak (born 1983), opera singer, baritone
 * Iva Kramperová (born 1984), classical violinist
 * Tomáš Nosek (born 1992), ice hockey player
 * Kovy (born 1996), youtuber
 * Filip Zadina (born 1999), ice hockey player

Twin towns – sister cities
Pardubice is twinned with:

 * 🇵🇱 Bełchatów, Poland
 * 🇹🇷 Çanakkale, Turkey
 * Doetinchem, Netherlands
 * 🇮🇹 Merano, Italy
 * 🇧🇬 Pernik, Bulgaria
 * 🇮🇹 Rosignano Marittimo, Italy
 * 🇩🇪 Selb, Germany
 * 🇸🇪 Skellefteå, Sweden
 * 🇸🇰 Vysoké Tatry, Slovakia

Cooperation agreements
Pardubice also cooperates with:

 * East Lothian, Scotland, United Kingdom
 * Golegã, Portugal
 * 🇪🇸 Jerez de la Frontera, Spain
 * 🇸🇮 Sežana, Slovenia
 * 🇧🇪 Waregem, Belgium
 * 🇵🇱 Wrocław, Poland

title: Pardubice