text:
Gravitational redshift

In physics and general relativity, gravitational redshift (known as Einstein shift in older literature) is the phenomenon that electromagnetic waves or photons travelling out of a gravitational well lose energy. This loss of energy corresponds to a decrease in the wave frequency and increase in the wavelength, known more generally as a redshift. The opposite effect, in which photons gain energy when travelling into a gravitational well, is known as a gravitational blueshift (a type of blueshift). The effect was first described by Einstein in 1907, eight years before his publication of the full theory of relativity.

Gravitational redshift can be interpreted as a consequence of the equivalence principle (that gravity and acceleration are equivalent and the redshift is caused by the Doppler effect) or as a consequence of the mass–energy equivalence and conservation of energy ('falling' photons gain energy), though there are numerous subtleties that complicate a rigorous derivation. A gravitational redshift can also equivalently be interpreted as gravitational time dilation at the source of the radiation: if two oscillators (attached to transmitters producing electromagnetic radiation) are operating at different gravitational potentials, the oscillator at the higher gravitational potential (farther from the attracting body) will tick faster; that is, when observed from the same location, it will have a higher measured frequency than the oscillator at the lower gravitational potential (closer to the attracting body).

To first approximation, gravitational redshift is proportional to the difference in gravitational potential divided by the speed of light squared, $$z = \Delta U / c^2$$, thus resulting in a very small effect. Light escaping from the surface of the Sun was predicted by Einstein in 1911 to be redshifted by roughly 2 ppm or 2 × 10−6. Navigational signals from GPS satellites orbiting at 20,000 km altitude are perceived blueshifted by approximately 0.5 ppb or 5 × 10−10, corresponding to a (negligible) increase of less than 1 Hz in the frequency of a 1.5 GHz GPS radio signal (however, the accompanying gravitational time dilation affecting the atomic clock in the satellite is crucially important for accurate navigation ). On the surface of the Earth the gravitational potential is proportional to height, $$\Delta U = g \Delta h$$, and the corresponding redshift is roughly 10−16 (0.1 part per quadrillion) per meter of change in elevation and/or altitude.

In astronomy, the magnitude of a gravitational redshift is often expressed as the velocity that would create an equivalent shift through the relativistic Doppler effect. In such units, the 2 ppm sunlight redshift corresponds to a 633 m/s receding velocity, roughly of the same magnitude as convective motions in the Sun, thus complicating the measurement. The GPS satellite gravitational blueshift velocity equivalent is less than 0.2 m/s, which is negligible compared to the actual Doppler shift resulting from its orbital velocity. In astronomical objects with strong gravitational fields the redshift can be much greater; for example, light from the surface of a white dwarf is gravitationally redshifted on average by around 50 km/s/c (around 170 ppm).

Observing the gravitational redshift in the Solar System is one of the classical tests of general relativity. Measuring the gravitational redshift to high precision with atomic clocks can serve as a test of Lorentz symmetry and guide searches for dark matter.

Uniform gravitational field or acceleration
Einstein's theory of general relativity incorporates the equivalence principle, which can be stated in various different ways. One such statement is that gravitational effects are locally undetectable for a free-falling observer. Therefore, in a laboratory experiment at the surface of the Earth, all gravitational effects should be equivalent to the effects that would have been observed if the laboratory had been accelerating through outer space at g. One consequence is a gravitational Doppler effect. If a light pulse is emitted at the floor of the laboratory, then a free-falling observer says that by the time it reaches the ceiling, the ceiling has accelerated away from it, and therefore when observed by a detector fixed to the ceiling, it will be observed to have been Doppler shifted toward the red end of the spectrum. This shift, which the free-falling observer considers to be a kinematical Doppler shift, is thought of by the laboratory observer as a gravitational redshift. Such an effect was verified in the 1959 Pound–Rebka experiment. In a case such as this, where the gravitational field is uniform, the change in wavelength is given by

 * $$z = \frac{\Delta\lambda}{\lambda}\approx \frac{g\Delta y}{c^2},$$

where $$\Delta y$$ is the change in height. Since this prediction arises directly from the equivalence principle, it does not require any of the mathematical apparatus of general relativity, and its verification does not specifically support general relativity over any other theory that incorporates the equivalence principle.

On Earth's surface (or in a spaceship accelerating at 1 g), the gravitational redshift is approximately 1.1 × 10−16, the equivalent of a 3.3 × 10−8 m/s Doppler shift, for every meter of height differential.

Spherically symmetric gravitational field
When the field is not uniform, the simplest and most useful case to consider is that of a spherically symmetric field. By Birkhoff's theorem, such a field is described in general relativity by the Schwarzschild metric, $$d\tau^2 = \left(1 - r_\text{S}/R\right)dt^2 + \ldots$$, where $$d\tau$$ is the clock time of an observer at distance R from the center, $$dt$$ is the time measured by an observer at infinity, $$r_\text{S}$$ is the Schwarzschild radius $$2GM/c^2$$, "..." represents terms that vanish if the observer is at rest, $$G$$ is Newton's gravitational constant, $$M$$ the mass of the gravitating body, and $$c$$ the speed of light. The result is that frequencies and wavelengths are shifted according to the ratio

 * $$1 + z = \frac{\lambda_\infty}{\lambda_\text{e}} = \left(1 - \frac{r_\text{S}}{R_\text{e}}\right)^{-\frac{1}{2}}$$

where
 * $$\lambda_\infty\,$$is the wavelength of the light as measured by the observer at infinity,
 * $$\lambda_\text{e}\,$$ is the wavelength measured at the source of emission, and
 * $$R_\text{e}$$ is the radius at which the photon is emitted.

This can be related to the redshift parameter conventionally defined as $$z = \lambda_\infty/\lambda_\text{e} - 1$$.

In the case where neither the emitter nor the observer is at infinity, the transitivity of Doppler shifts allows us to generalize the result to $$\lambda_1/\lambda_2 = \left[\left(1 - r_\text{S}/R_1\right)/\left(1 - r_\text{S}/R_2\right)\right]^{1/2}$$. The redshift formula for the frequency $$\nu = c/\lambda$$ is $$\nu_o/\nu_\text{e} = \lambda_\text{e}/\lambda_o$$. When $$R_1 - R_2$$ is small, these results are consistent with the equation given above based on the equivalence principle.

The redshift ratio may also be expressed in terms of a (Newtonian) escape velocity $$v_\text{e}$$ at $$R_\text{e} = 2GM/v_\text{e}^2$$, resulting in the corresponding Lorentz factor:

 * $$1 + z = \gamma_\text{e} = \frac{1}{\sqrt{1 - (v_\text{e}/c)^2}}$$.

For an object compact enough to have an event horizon, the redshift is not defined for photons emitted inside the Schwarzschild radius, both because signals cannot escape from inside the horizon and because an object such as the emitter cannot be stationary inside the horizon, as was assumed above. Therefore, this formula only applies when $$R_\text{e}$$ is larger than $$r_\text{S}$$. When the photon is emitted at a distance equal to the Schwarzschild radius, the redshift will be infinitely large, and it will not escape to any finite distance from the Schwarzschild sphere. When the photon is emitted at an infinitely large distance, there is no redshift.

Newtonian limit
In the Newtonian limit, i.e. when $$R_\text{e}$$ is sufficiently large compared to the Schwarzschild radius $$r_\text{S}$$, the redshift can be approximated as

 * $$z = \frac{\Delta\lambda}{\lambda} \approx \frac{1}{2}\frac{r_\text{S}}{R_\text{e}} = \frac{GM}{R_\text{e} c^2} = \frac{g R_\text{e}}{c^2}$$

where $$g$$ is the gravitational acceleration at $$R_\text{e}$$. For Earth's surface with respect to infinity, z is approximately 7 × 10−10 (the equivalent of a 0.2 m/s radial Doppler shift); for the Moon it is approximately 3 × 10−11 (about 1 cm/s). The value for the surface of the Sun is about 2 × 10−6, corresponding to 0.64 km/s. (For non-relativistic velocities, the radial Doppler equivalent velocity can be approximated by multiplying z with the speed of light.)

The z-value can be expressed succinctly in terms of the escape velocity at $$R_\text{e}$$, since the gravitational potential is equal to half the square of the escape velocity, thus:

 * $$z \approx \frac{1}{2}\left( \frac{v_\text{e}}{c} \right)^2$$

where $$v_\text{e}$$ is the escape velocity at $$R_\text{e}$$.

It can also be related to the circular orbit velocity $$v_\text{o}$$ at $$R_\text{e}$$, which equals $$v_\text{e}/\sqrt{2}$$, thus

 * $$z \approx \left( \frac{v_\text{o}}{c} \right)^2$$.

For example, the gravitational blueshift of distant starlight due to the Sun's gravity, which the Earth is orbiting at about 30 km/s, would be approximately 1 × 10−8 or the equivalent of a 3 m/s radial Doppler shift.

For an object in a (circular) orbit, the gravitational redshift is of comparable magnitude as the transverse Doppler effect, $$z \approx \tfrac{1}{2} \beta^2$$ where β=v/c, while both are much smaller than the radial Doppler effect, for which $$z \approx \beta$$.

Prediction of the Newtonian limit using the properties of photons
The formula for the gravitational red shift in the Newtonian limit can also be derived using the properties of a photon:

In a gravitational field $$\vec{g}$$ a particle of mass $$m$$ and velocity $$\vec{v}$$ changes it's  energy $$E$$ according to:

 * $$\frac{\mathrm dE}{\mathrm dt} = m \vec{g}\cdot \vec{v} = \vec{g}\cdot\vec{p}$$.

For a massless photon described by its energy $$E = h \nu = \hbar \omega$$ and momentum  $$\vec{p} = \hbar\vec{k}$$ this equation becomes after dividing by  Planck's constant $$\hbar$$:

 * $$\frac{\mathrm d \omega}{\mathrm dt} = \vec{g}\cdot \vec{k}$$

Inserting the gravitational field of a spherical body of mass $$M$$ within the distance $$\vec{r}$$

 * $$\vec{g} = -G M \frac{\vec{r}}{r^3}$$

and the wave vector of a photon leaving the gravitational field in radial direction

 * $$\vec{k} = \frac{\omega}{c} \frac{\vec{r}}{r}$$

the energy equation becomes
 * $$\frac{\mathrm d \omega}{\mathrm dt} = -\frac{G M}{c} \frac{\omega}{r^2}.$$

Using $$\mathrm dr = c \,\mathrm dt$$ an ordinary differential equation which is only dependent on the radial distance $$r$$ is obtained:

$$\frac{\mathrm d \omega}{\mathrm dr} = -\frac{G M}{c^2} \frac{\omega}{r^2} $$

For a photon starting at the surface of a spherical body with a Radius $$R_e$$ with a frequency $$\omega_0 = 2 \pi \nu_0$$ the analytical solution is:

$$\frac{\mathrm d \omega}{\mathrm dr} = -\frac{G M}{c^2} \frac{\omega}{r^2} \quad \Rightarrow \quad \omega(r) = \omega_0 \exp \left ( -\frac{G M}{c^2} \left( \frac{1}{R_e} - \frac{1}{r} \right) \right) $$

In a large distance from the body $$r \rightarrow \infty$$ an observer measures the frequency :

 * $$\omega_\text{obs} = \omega_0 \exp \left ( -\frac{G M}{c^2} \left( \frac{1}{R_e} \right) \right) \simeq \omega_0 \left( 1 - \frac{G M}{R_e c^2} + \frac{1}{2} \frac{G^2 M^2}{R_e^2 c^4} - \ldots \right). $$

Therefore the red shift is:
 * $$ z = \frac{\omega_0 - \omega_\text{obs}}{\omega_\text{obs}}

= \frac{1 - \exp \left( -\frac{G M}{R_e c^2} \right)}{\exp \left( -\frac{G M}{R_e c^2} \right)} = \frac{1 - \exp \left( -\frac{r_S}{2 R_e} \right)}{\exp \left( -\frac{r_S}{2 R_e} \right)} $$

In the linear approximation

 * $$z = \frac{ \frac{G M}{R_e c^2} - \frac{1}{2} \frac{G^2 M^2}{R_e^2 c^4} + \dots}{ 1 - \frac{G M}{R_e c^2} + \frac{1}{2} \frac{G^2 M^2}{R_e^2 c^4} - \ldots } \simeq \frac{ \frac{G M}{R_e c^2} }{ 1 - \frac{G M}{R_e c^2} + \frac{1}{2} \frac{G^2 M^2}{R_e^2 c^4} - \dots} \simeq \frac{G M}{c^2 R_e} $$

the Newtonian limit for the graviational red shift of General Relativity is obtained.

Astronomical observations
A number of experimenters initially claimed to have identified the effect using astronomical measurements, and the effect was considered to have been finally identified in the spectral lines of the star Sirius B by W.S. Adams in 1925. However, measurements by Adams have been criticized as being too low and these observations are now considered to be measurements of spectra that are unusable because of scattered light from the primary, Sirius A. The first accurate measurement of the gravitational redshift of a white dwarf was done by Popper in 1954, measuring a 21 km/s gravitational redshift of 40 Eridani B. The redshift of Sirius B was finally measured by Greenstein et al. in 1971, obtaining the value for the gravitational redshift of 89±16 km/s, with more accurate measurements by the Hubble Space Telescope, showing 80.4±4.8 km/s.

James W. Brault, a graduate student of Robert Dicke at Princeton University, measured the gravitational redshift of the sun using optical methods in 1962. In 2020, a team of scientists published the most accurate measurement of the solar gravitational redshift so far, made by analyzing Fe spectral lines in sunlight reflected by the Moon; their measurement of a mean global 638 ± 6 m/s lineshift is in agreement with the theoretical value of 633.1 m/s. Measuring the solar redshift is complicated by the Doppler shift caused by the motion of the Sun's surface, which is of similar magnitude as the gravitational effect.

In 2011, the group of Radek Wojtak of the Niels Bohr Institute at the University of Copenhagen collected data from 8000 galaxy clusters and found that the light coming from the cluster centers tended to be red-shifted compared to the cluster edges, confirming the energy loss due to gravity.

In 2018, the star S2 made its closest approach to Sgr A*, the 4-million solar mass supermassive black hole at the centre of the Milky Way, reaching 7650 km/s or about 2.5% of the speed of light while passing the black hole at a distance of just 120 AU, or 1400 Schwarzschild radii. Independent analyses by the GRAVITY collaboration   (led by Reinhard Genzel) and the KECK/UCLA Galactic Center Group  (led by Andrea Ghez) revealed a combined transverse Doppler and gravitational redshift up to 200 km/s/c, in agreement with general relativity predictions.

In 2021, Mediavilla (IAC, Spain) & Jiménez-Vicente (UGR, Spain) were able to use measurements of the gravitational redshift in quasars up to cosmological redshift of z~3 to confirm the predictions of Einstein's Equivalence Principle and the lack of cosmological evolution within 13%.

In 2024, Padilla et al. have estimated the gravitational redshifts of supermassive black holes (SMBH) in eight thousand quasars and one hundred Seyfert type 1 galaxies from the full width at half maximum (FWHM) of their emission lines, finding log z ≈ -4, compatible with SMBHs of ~ 1 billion solar masses and broadline regions of ~ 1 parsec radius. This same gravitational redshift was directly measured by these authors in the SAMI sample of LINER galaxies, using the redshift differences between lines emitted in central and outer regions.

Terrestrial tests
The effect is now considered to have been definitively verified by the experiments of Pound, Rebka and Snider between 1959 and 1965. The Pound–Rebka experiment of 1959 measured the gravitational redshift in spectral lines using a terrestrial 57Fe gamma source over a vertical height of 22.5 metres. This paper was the first determination of the gravitational redshift which used measurements of the change in wavelength of gamma-ray photons generated with the Mössbauer effect, which generates radiation with a very narrow line width. The accuracy of the gamma-ray measurements was typically 1%.

An improved experiment was done by Pound and Snider in 1965, with an accuracy better than the 1% level.

A very accurate gravitational redshift experiment was performed in 1976, where a hydrogen maser clock on a rocket was launched to a height of 10,000 km, and its rate compared with an identical clock on the ground. It tested the gravitational redshift to 0.007%.

Later tests can be done with the Global Positioning System (GPS), which must account for the gravitational redshift in its timing system, and physicists have analyzed timing data from the GPS to confirm other tests. When the first satellite was launched, it showed the predicted shift of 38 microseconds per day. This rate of the discrepancy is sufficient to substantially impair the function of GPS within hours if not accounted for. An excellent account of the role played by general relativity in the design of GPS can be found in Ashby 2003.

In 2010, an experiment placed two aluminum-ion quantum clocks close to each other, but with the second elevated 33 cm compared to the first, making the gravitational red shift effect visible in everyday lab scales.

In 2020, a group at the University of Tokyo measured the gravitational redshift of two strontium-87 optical lattice clocks. The measurement took place at Tokyo Skytree where the clocks were separated by approximately 450 m and connected by telecom fibers. The gravitational redshift can be expressed as

 * $$ z = \frac{\Delta\nu}{\nu_{1}} = (1+\alpha)\frac{\Delta U}{c^2} $$,

where $$\Delta\nu=\nu_{2}-\nu_{1}$$ is the gravitational redshift, $$\nu_{1}$$ is the optical clock transition frequency, $$\Delta U= U_{2}- U_{1}$$ is the difference in gravitational potential, and $$\alpha$$ denotes the violation from general relativity. By Ramsey spectroscopy of the strontium-87 optical clock transition (429 THz, 698 nm) the group determined the gravitational redshift between the two optical clocks to be 21.18 Hz, corresponding to a z-value of approximately 5 × 10−14. Their measured value of $$\alpha$$, $$(1.4 \pm 9.1)\times 10^{-5} $$, is an agreement with recent measurements made with hydrogen masers in elliptical orbits.

In October 2021, a group at JILA led by physicist Jun Ye reported a measurement of gravitational redshift in the submillimeter scale. The measurement is done on the 87Sr clock transition between the top and the bottom of a millimeter-tall ultracold cloud of 100,000 strontium atoms in an optical lattice.

Early historical development of the theory
The gravitational weakening of light from high-gravity stars was predicted by John Michell in 1783 and Pierre-Simon Laplace in 1796, using Isaac Newton's concept of light corpuscles (see: emission theory) and who predicted that some stars would have a gravity so strong that light would not be able to escape. The effect of gravity on light was then explored by Johann Georg von Soldner (1801), who calculated the amount of deflection of a light ray by the Sun, arriving at the Newtonian answer which is half the value predicted by general relativity. All of this early work assumed that light could slow down and fall, which is inconsistent with the modern understanding of light waves.

Once it became accepted that light was an electromagnetic wave, it was clear that the frequency of light should not change from place to place, since waves from a source with a fixed frequency keep the same frequency everywhere. One way around this conclusion would be if time itself were altered – if clocks at different points had different rates. This was precisely Einstein's conclusion in 1911. He considered an accelerating box, and noted that according to the special theory of relativity, the clock rate at the "bottom" of the box (the side away from the direction of acceleration) was slower than the clock rate at the "top" (the side toward the direction of acceleration). Indeed, in a frame moving (in $$x$$ direction) with velocity $$v$$ relative to the rest frame, the clocks at a nearby position $$dx$$ are ahead by $$(dx/c)(v/c)$$ (to the first order); so an acceleration $$g$$ (that changes speed by $$g/dt$$ per time $$dt$$) makes clocks at the position $$dx$$ to be ahead by $$(dx/c)(g/c)dt$$, that is, tick at a rate

R=1+(g/c^2)dx $$

The equivalence principle implies that this change in clock rate is the same whether the acceleration $$g$$ is that of an accelerated frame without gravitational effects, or caused by a gravitational field in a stationary frame. Since acceleration due to gravitational potential $$V$$ is $$-dV/dx$$, we get

{dR \over dx} = g/c^2 = - {dV/c^2 \over dx} \,$$ so – in weak fields – the change $$\Delta R$$ in the clock rate is equal to $$-\Delta V/c^2$$.

Since the light would be slowed down by gravitational time dilation (as seen by outside observer), the regions with lower gravitational potential would act like a medium with higher refractive index causing light to deflect. This reasoning allowed Einstein in 1911 to reproduce the incorrect Newtonian value for the deflection of light. At the time he only considered the time-dilating manifestation of gravity, which is the dominating contribution at non-relativistic speeds; however relativistic objects travel through space a comparable amount as they do though time, so purely spatial curvature becomes just as important. After constructing the full theory of general relativity, Einstein solved in 1915 the full post-Newtonian approximation for the Sun's gravity and calculated the correct amount of light deflection – double the Newtonian value. Einstein's prediction was confirmed by many experiments, starting with Arthur Eddington's 1919 solar eclipse expedition.

The changing rates of clocks allowed Einstein to conclude that light waves change frequency as they move, and the frequency/energy relationship for photons allowed him to see that this was best interpreted as the effect of the gravitational field on the mass–energy of the photon. To calculate the changes in frequency in a nearly static gravitational field, only the time component of the metric tensor is important, and the lowest order approximation is accurate enough for ordinary stars and planets, which are much bigger than their Schwarzschild radius.

title: Gravitational redshift


text:
Easter Rising

The Easter Rising (Éirí Amach na Cásca), also known as the Easter Rebellion, was an armed insurrection in Ireland during Easter Week in April 1916. The Rising was launched by Irish republicans against British rule in Ireland with the aim of establishing an independent Irish Republic while the United Kingdom was fighting the First World War. It was the most significant uprising in Ireland since the rebellion of 1798 and the first armed conflict of the Irish revolutionary period. Sixteen of the Rising's leaders were executed starting in May 1916. The nature of the executions, and subsequent political developments, ultimately contributed to an increase in popular support for Irish independence.

Organised by a seven-man Military Council of the Irish Republican Brotherhood, the Rising began on Easter Monday, 24 April 1916 and lasted for six days. Members of the Irish Volunteers, led by schoolmaster and Irish language activist Patrick Pearse, joined by the smaller Irish Citizen Army of James Connolly and 200 women of Cumann na mBan seized strategically important buildings in Dublin and proclaimed the Irish Republic. The British Army brought in thousands of reinforcements as well as artillery and a gunboat. There was street fighting on the routes into the city centre, where the rebels slowed the British advance and inflicted many casualties. Elsewhere in Dublin, the fighting mainly consisted of sniping and long-range gun battles. The main rebel positions were gradually surrounded and bombarded with artillery. There were isolated actions in other parts of Ireland; Volunteer leader Eoin MacNeill had issued a countermand in a bid to halt the Rising, which greatly reduced the extent of the rebel actions.

With much greater numbers and heavier weapons, the British Army suppressed the Rising. Pearse agreed to an unconditional surrender on Saturday 29 April, although sporadic fighting continued briefly. After the surrender, the country remained under martial law. About 3,500 people were taken prisoner by the British and 1,800 of them were sent to internment camps or prisons in Britain. Most of the leaders of the Rising were executed following courts martial. The Rising brought physical force republicanism back to the forefront of Irish politics, which for nearly fifty years had been dominated by constitutional nationalism. Opposition to the British reaction to the Rising contributed to changes in public opinion and the move toward independence, as shown in the December 1918 election in Ireland which was won by the Sinn Féin party, which convened the First Dáil and declared independence.

Of the 485 people killed, 260 were civilians, 143 were British military and police personnel, and 82 were Irish rebels, including 16 rebels executed for their roles in the Rising. More than 2,600 people were wounded. Many of the civilians were killed or wounded by British artillery fire or were mistaken for rebels. Others were caught in the crossfire during firefights between the British and the rebels. The shelling and resulting fires left parts of central Dublin in ruins.

Background

The Acts of Union 1800 united the Kingdom of Great Britain and the Kingdom of Ireland as the United Kingdom of Great Britain and Ireland, abolishing the Irish Parliament and giving Ireland representation in the British Parliament. From early on, many Irish nationalists opposed the union and the continued lack of adequate political representation, along with the British government's handling of Ireland and Irish people, particularly the Great Famine. The union was closely preceded by and formed partly in response to an Irish uprising – whose centenary would prove an influence on the Easter Rising. Three more rebellions ensued: one in 1803, another in 1848 and one in 1867. All were failures.

Opposition took other forms: constitutional (the Repeal Association; the Home Rule League) and social (disestablishment of the Church of Ireland; the Land League). The Irish Home Rule movement sought to achieve self-government for Ireland, within the United Kingdom. In 1886, the Irish Parliamentary Party under Charles Stewart Parnell succeeded in having the First Home Rule Bill introduced in the British parliament, but it was defeated. The Second Home Rule Bill of 1893 was passed by the House of Commons but rejected by the House of Lords.

After the death of Parnell, younger and more radical nationalists became disillusioned with parliamentary politics and turned toward more extreme forms of separatism. The Gaelic Athletic Association, the Gaelic League, and the cultural revival under W. B. Yeats and Augusta, Lady Gregory, together with the new political thinking of Arthur Griffith expressed in his newspaper Sinn Féin and organisations such as the National Council and the Sinn Féin League, led many Irish people to identify with the idea of an independent Gaelic Ireland.

The Third Home Rule Bill was introduced by British Liberal Prime Minister H. H. Asquith in 1912. Irish Unionists, who were overwhelmingly Protestants, opposed it, as they did not want to be ruled by a Catholic-dominated Irish government. Led by Sir Edward Carson and James Craig, they formed the Ulster Volunteers (UVF) in January 1913. The UVF's opposition included arming themselves, in the event that they had to resist by force.

Seeking to defend Home Rule, the Irish Volunteers was formed in November 1913. Although sporting broadly open membership and without avowed support for separatism, the executive branch of the Irish Volunteers – excluding leadership – was dominated by the Irish Republican Brotherhood (IRB) who rose to prominence via the organisation, having had restarted recruitment in 1909. These members feared that Home Rule's enactment would result in a broad, seemingly perpetual, contentment with the British Empire. Another militant group, the Irish Citizen Army, was formed by trade unionists as a result of the Dublin Lock-out of that year. The issue of Home Rule, appeared to some, as the basis of an "imminent civil war".

Although the Third Home Rule Bill was eventually enacted, the outbreak of the First World War resulted in its implementation being postponed for the war's duration. It was widely believed at the time that the war would not last more than a few months. The Irish Volunteers split. The vast majority – thereafter known as the National Volunteers – enlisted in the British Army. The minority that objected – retaining the name – did so in accordance with separatist principles, official policy thus becoming "the abolition of the system of governing Ireland through Dublin Castle and the British military power and the establishment of a National Government in its place"; the Volunteers believed that "England's difficulty" was "Ireland's opportunity".

Planning the Rising
The Supreme Council of the IRB met on 5 September 1914, just over a month after the British government had declared war on Germany. At this meeting, they elected to stage an uprising before the war ended and to secure help from Germany. Responsibility for the planning of the rising was given to Tom Clarke and Seán Mac Diarmada. Patrick Pearse, Michael Joseph O’Rahilly, Joseph Plunkett and Bulmer Hobson would assume general control of the Volunteers by March 1915.

In May 1915, Clarke and Mac Diarmada established a Military Council within the IRB, consisting of Pearse, Plunkett and Éamonn Ceannt – and soon themselves – to devise plans for a rising. The Military Council functioned independently and in opposition to those who considered a possible uprising inopportune. Volunteer Chief-of-Staff Eoin MacNeill supported a rising only if the British government attempted to suppress the Volunteers or introduce conscription in Ireland, and if such a rising had some chance of success. Hobson and IRB President Denis McCullough held similar views as did much of the executive branches of both organisations.

The Military Council kept its plans secret, so as to prevent the British authorities from learning of the plans, and to thwart those within the organisation who might try to stop the rising. The secrecy of the plans was such that the Military Council largely superseded the IRB's Supreme Council with even McCullough being unaware of some of the plans, whereas the likes of MacNeill were only informed as the Rising rapidly approached. Although most Volunteers were oblivious to any plans their training increased in the preceding year. The public nature of their training heightened tensions with authorities, which, come the next year, manifested in rumours of the Rising. Public displays likewise existed in the espousal of anti-recruitment. The number of Volunteers also increased: between December 1914 and February 1916 the rank and file rose from 9,700 to 12,215. Although the likes of the civil servants were discouraged from joining the Volunteers, the organisation was permitted by law.

Shortly after the outbreak of World War I, Roger Casement and John Devoy went to Germany and began negotiations with the German government and military. Casement – later accompanied by Plunkett – persuaded the Germans to announce their support for Irish independence in November 1914. Casement envisioned the recruitment of Irish prisoners of war, to be known as the Irish Brigade, aided by a German expeditionary force who would secure the line of the River Shannon, before advancing on the capital. Neither intention came to fruition, but the German military did agree to ship arms and ammunition to the Volunteers, gunrunning having become difficult and dangerous on account of the war.

In late 1915 and early 1916 Devoy had trusted couriers deliver approximately $100,000 from the American based Irish Republican organization Clan na Gael to the IRB. On 5 February 1916 Devoy received a coded message from the Supreme Council of the IRB informing him of their decision to start a rebellion at Easter 1916: "We have decided to begin action on Easter Sunday. We must have your arms and munitions in Limerick between Good Friday and Easter Sunday. We expect German help immediately after beginning action. We might have to begin earlier."

Head of the Irish Citizen Army, James Connolly, was unaware of the IRB's plans, and threatened to start a rebellion on his own if other parties failed to act. The IRB leaders met with Connolly in Dolphin's Barn in January 1916 and convinced him to join forces with them. They agreed that they would launch a rising together at Easter and made Connolly the sixth member of the Military Council. Thomas MacDonagh would later become the seventh and final member.

The death of the old Fenian leader Jeremiah O'Donovan Rossa in New York City in August 1915 was an opportunity to mount a spectacular demonstration. His body was sent to Ireland for burial in Glasnevin Cemetery, with the Volunteers in charge of arrangements. Huge crowds lined the route and gathered at the graveside. Pearse (wearing the uniform of the Irish Volunteers) made a dramatic funeral oration, a rallying call to republicans, which ended with the words "Ireland unfree shall never be at peace".

Build-up to Easter Week
In early April, Pearse issued orders to the Irish Volunteers for three days of "parades and manoeuvres" beginning on Easter Sunday. He had the authority to do this, as the Volunteers' Director of Organisation. The idea was that IRB members within the organisation would know these were orders to begin the rising, while men such as MacNeill and the British authorities would take it at face value.

On 9 April, the German Navy dispatched the SS Libau for County Kerry, disguised as the Norwegian ship Aud. It was loaded with 20,000 rifles, one million rounds of ammunition, and explosives. Casement also left for Ireland aboard the German submarine U-19. He was disappointed with the level of support offered by the Germans and he intended to stop or at least postpone the rising. During this time, the Volunteers amassed ammunition from various sources, including the adolescent Michael McCabe.

On Wednesday 19 April, Alderman Tom Kelly, a Sinn Féin member of Dublin Corporation, read out at a meeting of the corporation a document purportedly leaked from Dublin Castle, detailing plans by the British authorities to shortly arrest leaders of the Irish Volunteers, Sinn Féin and the Gaelic League, and occupy their premises. Although the British authorities said the "Castle Document" was fake, MacNeill ordered the Volunteers to prepare to resist. Unbeknownst to MacNeill, the document had been forged by the Military Council to persuade moderates of the need for their planned uprising. It was an edited version of a real document outlining British plans in the event of conscription. That same day, the Military Council informed senior Volunteer officers that the rising would begin on Easter Sunday. However, it chose not to inform the rank-and-file, or moderates such as MacNeill, until the last minute.

The following day, MacNeill got wind that a rising was about to be launched and threatened to do everything he could to prevent it, short of informing the British. He and Hobson confronted Pearse, but refrained from decisive action as to avoiding instigating a rebellion of any kind; Hobson would be detained by Volunteers until the Rising occurred.

The SS Libau (disguised as the Aud) and the U-19 reached the coast of Kerry on Good Friday, 21 April. This was earlier than the Volunteers expected and so none were there to meet the vessels. The Royal Navy had known about the arms shipment and intercepted the SS Libau, prompting the captain to scuttle the ship. Furthermore, Casement was captured shortly after he landed at Banna Strand.

When MacNeill learned that the arms shipment had been lost, he reverted to his original position. With the support of other leaders of like mind, notably Bulmer Hobson and The O'Rahilly, he issued a countermand to all Volunteers, cancelling all actions for Sunday. This countermanding order was relayed to Volunteer officers and printed in the Sunday morning newspapers. The order resulted in a delay to the rising by a day, and some confusion over strategy for those who took part.

British Naval Intelligence had been aware of the arms shipment, Casement's return, and the Easter date for the rising through radio messages between Germany and its embassy in the United States that were intercepted by the Royal Navy and deciphered in Room 40 of the Admiralty. It is unclear how extensive Room 40's decryptions preceding the Rising were. On the eve of the Rising, John Dillon wrote to Redmond of Dublin being "full of most extraordinary rumours. And I have no doubt in my mind that the Clan men – are planning some devilish business – what it is I cannot make out. It may not come off – But you must not be surprised if something very unpleasant and mischievous happens this week".

The information was passed to the Under-Secretary for Ireland, Sir Matthew Nathan, on 17 April, but without revealing its source; Nathan was doubtful about its accuracy. When news reached Dublin of the capture of the SS Libau and the arrest of Casement, Nathan conferred with the Lord Lieutenant, Lord Wimborne. Nathan proposed to raid Liberty Hall, headquarters of the Citizen Army, and Volunteer properties at Father Matthew Park and at Kimmage, but Wimborne insisted on wholesale arrests of the leaders. It was decided to postpone action until after Easter Monday, and in the meantime, Nathan telegraphed the Chief Secretary, Augustine Birrell, in London seeking his approval. By the time Birrell cabled his reply authorising the action, at noon on Monday 24 April 1916, the Rising had already begun.

On the morning of Easter Sunday, 23 April, the Military Council met at Liberty Hall to discuss what to do in light of MacNeill's countermanding order. They decided that the Rising would go ahead the following day, Easter Monday, and that the Irish Volunteers and Irish Citizen Army would go into action as the 'Army of the Irish Republic'. They elected Pearse as president of the Irish Republic, and also as Commander-in-Chief of the army; Connolly became Commandant of the Dublin Brigade. That weekend was largely spent preparing rations and manufacturing ammunition and bombs. Messengers were then sent to all units informing them of the new orders.

Easter Monday

On the morning of Monday 24 April, about 1,200 members of the Irish Volunteers and Irish Citizen Army mustered at several locations in central Dublin. Among them were members of the all-female Cumann na mBan. Some wore Irish Volunteer and Citizen Army uniforms, while others wore civilian clothes with a yellow Irish Volunteer armband, military hats, and bandoliers. They were armed mostly with rifles (especially 1871 Mausers), but also with shotguns, revolvers, a few Mauser C96 semi-automatic pistols, and grenades. The number of Volunteers who mobilised was much smaller than expected. This was due to MacNeill's countermanding order, and the fact that the new orders had been sent so soon beforehand. However, several hundred Volunteers joined the Rising after it began.

Shortly before midday, the rebels began to seize important sites in central Dublin. The rebels' plan was to hold Dublin city centre. This was a large, oval-shaped area bounded by two canals: the Grand to the south and the Royal to the north, with the River Liffey running through the middle. On the southern and western edges of this district were five British Army barracks. Most of the rebels' positions had been chosen to defend against counter-attacks from these barracks. The rebels took the positions with ease. Civilians were evacuated and policemen were ejected or taken prisoner. Windows and doors were barricaded, food and supplies were secured, and first aid posts were set up. Barricades were erected on the streets to hinder British Army movement.

A joint force of about 400 Volunteers and the Citizen Army gathered at Liberty Hall under the command of Commandant James Connolly. This was the headquarters battalion, and it also included Commander-in-Chief Patrick Pearse, as well as Tom Clarke, Seán Mac Diarmada and Joseph Plunkett. They marched to the General Post Office (GPO) on O'Connell Street, Dublin's main thoroughfare, occupied the building and hoisted two republican flags. Pearse stood outside and read the Proclamation of the Irish Republic. Copies of the Proclamation were also pasted on walls and handed out to bystanders by Volunteers and newsboys. The GPO would be the rebels' headquarters for most of the Rising. Volunteers from the GPO also occupied other buildings on the street, including buildings overlooking O'Connell Bridge. They took over a wireless telegraph station and sent out a radio broadcast in Morse code, announcing that an Irish Republic had been declared. This was the first radio broadcast in Ireland.

Elsewhere, some of the headquarters battalion under Michael Mallin occupied St Stephen's Green, where they dug trenches and barricaded the surrounding roads. The 1st battalion, under Edward 'Ned' Daly, occupied the Four Courts and surrounding buildings, while a company under Seán Heuston occupied the Mendicity Institution, across the River Liffey from the Four Courts. The 2nd battalion, under Thomas MacDonagh, occupied Jacob's biscuit factory. The 3rd battalion, under Éamon de Valera, occupied Boland's Mill and surrounding buildings (uniquely, without the presence of Cumann na mBan women whom de Valera expressly excluded). The 4th battalion, under Éamonn Ceannt, occupied the South Dublin Union and the distillery on Marrowbone Lane. From each of these garrisons, small units of rebels established outposts in the surrounding area.

The rebels also attempted to cut transport and communication links. As well as erecting roadblocks, they took control of various bridges and cut telephone and telegraph wires. Westland Row and Harcourt Street railway stations were occupied, though the latter only briefly. The railway line was cut at Fairview and the line was damaged by bombs at Amiens Street, Broadstone, Kingsbridge and Lansdowne Road.

Around midday, a small team of Volunteers and Fianna Éireann members swiftly captured the Magazine Fort in the Phoenix Park and disarmed the guards. The goal was to seize weapons and blow up the ammunition store to signal that the Rising had begun. They seized weapons and planted explosives, but the blast was not loud enough to be heard across the city. The 23-year-old son of the fort's commander was fatally shot when he ran to raise the alarm.

A contingent under Seán Connolly occupied Dublin City Hall and adjacent buildings. They attempted to seize neighbouring Dublin Castle, the heart of British rule in Ireland. As they approached the gate a lone and unarmed police sentry, James O'Brien, attempted to stop them and was shot dead by Connolly. According to some accounts, he was the first casualty of the Rising. The rebels overpowered the soldiers in the guardroom but failed to press further. The British Army's chief intelligence officer, Major Ivon Price, fired on the rebels while the Under-Secretary for Ireland, Sir Matthew Nathan, helped shut the castle gates. Unbeknownst to the rebels, the Castle was lightly guarded and could have been taken with ease. The rebels instead laid siege to the Castle from City Hall. Fierce fighting erupted there after British reinforcements arrived. The rebels on the roof exchanged fire with soldiers on the street. Seán Connolly was shot dead by a sniper, becoming the first rebel casualty. By the following morning, British forces had re-captured City Hall and taken the rebels prisoner.

The rebels did not attempt to take some other key locations, notably Trinity College, in the heart of the city centre and defended by only a handful of armed unionist students. Failure to capture the telephone exchange in Crown Alley left communications in the hands of the Government with GPO staff quickly repairing telephone wires that had been cut by the rebels. The failure to occupy strategic locations was attributed to lack of manpower. In at least two incidents, at Jacob's and Stephen's Green, the Volunteers and Citizen Army shot dead civilians trying to attack them or dismantle their barricades. Elsewhere, they hit civilians with their rifle butts to drive them off.

The British military were caught totally unprepared by the Rising and their response of the first day was generally un-coordinated. Two squadrons of British cavalry were sent to investigate what was happening. They took fire and casualties from rebel forces at the GPO and at the Four Courts. As one troop passed Nelson's Pillar, the rebels opened fire from the GPO, killing three cavalrymen and two horses and fatally wounding a fourth man. The cavalrymen retreated and were withdrawn to barracks. On Mount Street, a group of Volunteer Training Corps men stumbled upon the rebel position and four were killed before they reached Beggars Bush Barracks. Although ransacked, the barracks were never seized.

The only substantial combat of the first day of the Rising took place at the South Dublin Union where a piquet from the Royal Irish Regiment encountered an outpost of Éamonn Ceannt's force at the northwestern corner of the South Dublin Union. The British troops, after taking some casualties, managed to regroup and launch several assaults on the position before they forced their way inside and the small rebel force in the tin huts at the eastern end of the Union surrendered. However, the Union complex as a whole remained in rebel hands. A nurse in uniform, Margaret Keogh, was shot dead by British soldiers at the Union. She is believed to have been the first civilian killed in the Rising.

Three unarmed Dublin Metropolitan Police were shot dead on the first day of the Rising and their Commissioner pulled them off the streets. Partly as a result of the police withdrawal, a wave of looting broke out in the city centre, especially in the area of O'Connell Street (still officially called "Sackville Street" at the time).

Tuesday and Wednesday
Lord Wimborne, the Lord Lieutenant, declared martial law on Tuesday evening and handed over civil power to Brigadier-General William Lowe. British forces initially put their efforts into securing the approaches to Dublin Castle and isolating the rebel headquarters, which they believed was in Liberty Hall. The British commander, Lowe, worked slowly, unsure of the size of the force he was up against, and with only 1,269 troops in the city when he arrived from the Curragh Camp in the early hours of Tuesday 25 April. City Hall was taken from the rebel unit that had attacked Dublin Castle on Tuesday morning.

In the early hours of Tuesday, 120 British soldiers, with machine guns, occupied two buildings overlooking St Stephen's Green: the Shelbourne Hotel and United Services Club. At dawn they opened fire on the Citizen Army occupying the green. The rebels returned fire but were forced to retreat to the Royal College of Surgeons building. They remained there for the rest of the week, exchanging fire with British forces.

Fighting erupted along the northern edge of the city centre on Tuesday afternoon. In the northeast, British troops left Amiens Street railway station in an armoured train, to secure and repair a section of damaged tracks. They were attacked by rebels who had taken up position at Annesley Bridge. After a two-hour battle, the British were forced to retreat and several soldiers were captured. At Phibsborough, in the northwest, rebels had occupied buildings and erected barricades at junctions on the North Circular Road. The British summoned 18-pounder field artillery from Athlone and shelled the rebel positions, destroying the barricades. After a fierce firefight, the rebels withdrew.

That afternoon Pearse walked out into O'Connell Street with a small escort and stood in front of Nelson's Pillar. As a large crowd gathered, he read out a 'manifesto to the citizens of Dublin,' calling on them to support the Rising.

The rebels had failed to take either of Dublin's two main railway stations or either of its ports, at Dublin Port and Kingstown. As a result, during the following week, the British were able to bring in thousands of reinforcements from Britain and from their garrisons at the Curragh and Belfast. By the end of the week, British strength stood at over 16,000 men. Their firepower was provided by field artillery which they positioned on the Northside of the city at Phibsborough and at Trinity College, and by the patrol vessel Helga, which sailed up the Liffey, having been summoned from the port at Kingstown. On Wednesday, 26 April, the guns at Trinity College and Helga shelled Liberty Hall, and the Trinity College guns then began firing at rebel positions, first at Boland's Mill and then in O'Connell Street. Some rebel commanders, particularly James Connolly, did not believe that the British would shell the 'second city' of the British Empire.

The principal rebel positions at the GPO, the Four Courts, Jacob's Factory and Boland's Mill saw little action. The British surrounded and bombarded them rather than assault them directly. One Volunteer in the GPO recalled, "we did practically no shooting as there was no target". Entertainment ensued within the factory, "everybody merry & cheerful", bar the "occasional sniping", noted one Volunteer. However, where the rebels dominated the routes by which the British tried to funnel reinforcements into the city, there was fierce fighting.

At 5:25 PM a dozen Volunteers, including Eamon Martin, Garry Holohan, Robert Beggs, Sean Cody, Dinny O'Callaghan, Charles Shelley, and Peadar Breslin, attempted to occupy Broadstone railway station on Church Street. The attack was unsuccessful and Martin was injured.

On Wednesday morning, hundreds of British troops encircled the Mendicity Institution, which was occupied by 26 Volunteers under Seán Heuston. British troops advanced on the building, supported by snipers and machine-gun fire, but the Volunteers put up stiff resistance. Eventually, the troops got close enough to hurl grenades into the building, some of which the rebels threw back. Exhausted and almost out of ammunition, Heuston's men became the first rebel position to surrender. Heuston had been ordered to hold his position for a few hours, to delay the British, but had held on for three days.

Reinforcements were sent to Dublin from Britain and disembarked at Kingstown on the morning of Wednesday 26 April. Heavy fighting occurred at the rebel-held positions around the Grand Canal as these troops advanced towards Dublin. More than 1,000 Sherwood Foresters were repeatedly caught in a crossfire trying to cross the canal at Mount Street Bridge. Seventeen Volunteers were able to severely disrupt the British advance, killing or wounding 240 men. Despite there being alternative routes across the canal nearby, General Lowe ordered repeated frontal assaults on the Mount Street position. The British eventually took the position, which had not been reinforced by the nearby rebel garrison at Boland's Mills, on Thursday, but the fighting there inflicted up to two-thirds of their casualties for the entire week for a cost of just four dead Volunteers. It had taken nearly nine hours for the British to advance 300 yd.

On Wednesday Linenhall Barracks on Constitution Hill was burnt down under the orders of Commandant Edward Daly to prevent its reoccupation by the British.

Thursday to Saturday
The rebel position at the South Dublin Union (site of the present-day St. James's Hospital) and Marrowbone Lane, further west along the canal, also inflicted heavy losses on British troops. The South Dublin Union was a large complex of buildings and there was vicious fighting around and inside the buildings. Cathal Brugha, a rebel officer, distinguished himself in this action and was badly wounded. By the end of the week, the British had taken some of the buildings in the Union, but others remained in rebel hands. British troops also took casualties in unsuccessful frontal assaults on the Marrowbone Lane Distillery.

The third major scene of fighting during the week was in the area of North King Street, north of the Four Courts. The rebels had established strong outposts in the area, occupying numerous small buildings and barricading the streets. From Thursday to Saturday, the British made repeated attempts to capture the area, in what was some of the fiercest fighting of the Rising. As the troops moved in, the rebels continually opened fire from windows and behind chimneys and barricades. At one point, a platoon led by Major Sheppard made a bayonet charge on one of the barricades but was cut down by rebel fire. The British employed machine guns and attempted to avoid direct fire by using makeshift armoured trucks, and by mouse-holing through the inside walls of terraced houses to get near the rebel positions. By the time of the rebel headquarters' surrender on Saturday, the South Staffordshire Regiment under Colonel Taylor had advanced only 150 yd down the street at a cost of 11 dead and 28 wounded. The enraged troops broke into the houses along the street and shot or bayoneted fifteen unarmed male civilians whom they accused of being rebel fighters.

Elsewhere, at Portobello Barracks, an officer named Bowen Colthurst summarily executed six civilians, including the pacifist nationalist activist, Francis Sheehy-Skeffington. These instances of British troops killing Irish civilians would later be highly controversial in Ireland.

Surrender

The headquarters garrison at the GPO was forced to evacuate after days of shelling when a fire caused by the shells spread to the GPO. Connolly had been incapacitated by a bullet wound to the ankle and had passed command on to Pearse. The O'Rahilly was killed in a sortie from the GPO. They tunnelled through the walls of the neighbouring buildings in order to evacuate the Post Office without coming under fire and took up a new position in 16 Moore Street. The young Seán McLoughlin was given military command and planned a breakout, but Pearse realised this plan would lead to further loss of civilian life.

On the eve of the surrender, there had been about 35 Cumann na mBan women remaining in the GPO. In the final group that left with Pearse and Connolly, there were three: Connolly's aide de camp, Winifred Carney, who had entered with the original ICA contingent, and the dispatchers and nurses Elizabeth O'Farrell, and Julia Grenan.

On Saturday 29 April, from this new headquarters, Pearse issued an order for all companies to surrender. Pearse surrendered unconditionally to Brigadier-General Lowe. The surrender document read:

"In order to prevent the further slaughter of Dublin citizens, and in the hope of saving the lives of our followers now surrounded and hopelessly outnumbered, the members of the Provisional Government present at headquarters have agreed to an unconditional surrender, and the commandants of the various districts in the City and County will order their commands to lay down arms."

The other posts surrendered only after Pearse's surrender order, carried by O'Farrell, reached them. Sporadic fighting, therefore, continued until Sunday, when word of the surrender was got to the other rebel garrisons. Command of British forces had passed from Lowe to General John Maxwell, who arrived in Dublin just in time to take the surrender. Maxwell was made temporary military governor of Ireland.

The Rising outside Dublin
The Rising was planned to occur across the nation, but MacNeill's countermanding order coupled with the failure to secure German arms hindered this objective significantly. Charles Townshend contended that serious intentions for a national Rising were meagre, being diminished by a focus upon Dublin – although this is an increasingly contentious notion.

In the south, around 1,200 Volunteers commanded by Tomás Mac Curtain mustered on the Sunday in Cork, but they dispersed on Wednesday after receiving nine contradictory orders by dispatch from the Volunteer leadership in Dublin. At their Sheares Street headquarters, some of the Volunteers engaged in a standoff with British forces. Much to the anger of many Volunteers, MacCurtain, under pressure from Catholic clergy, agreed to surrender his men's arms to the British. The only violence in County Cork occurred when the RIC attempted to raid the home of the Kent family. The Kent brothers, who were Volunteers, engaged in a three-hour firefight with the RIC. An RIC officer and one of the brothers were killed, while another brother was later executed. Virtually all rebel family homes were raided, either during or after the Rising.

In the north, Volunteer companies were mobilised in County Tyrone at Coalisland (including 132 men from Belfast led by IRB President Dennis McCullough) and Carrickmore, under the leadership of Patrick McCartan. They also mobilised at Creeslough, County Donegal under Daniel Kelly and James McNulty. However, in part because of the confusion caused by the countermanding order, the Volunteers in these locations dispersed without fighting.

Ashbourne
In north County Dublin, about 60 Volunteers mobilised near Swords. They belonged to the 5th Battalion of the Dublin Brigade (also known as the Fingal Battalion), and were led by Thomas Ashe and his second in command, Richard Mulcahy. Unlike the rebels elsewhere, the Fingal Battalion successfully employed guerrilla tactics. They set up camp and Ashe split the battalion into four sections: three would undertake operations while the fourth was kept in reserve, guarding camp and foraging for food. The Volunteers moved against the RIC barracks in Swords, Donabate and Garristown, forcing the RIC to surrender and seizing all the weapons. They also damaged railway lines and cut telegraph wires. The railway line at Blanchardstown was bombed to prevent a troop train from reaching Dublin. This derailed a cattle train, which had been sent ahead of the troop train.

The only large-scale engagement of the Rising, outside Dublin city, was at Ashbourne, County Meath. On Friday, about 35 Fingal Volunteers surrounded the Ashbourne RIC barracks and called on it to surrender, but the RIC responded with a volley of gunfire. A firefight followed, and the RIC surrendered after the Volunteers attacked the building with a homemade grenade. Before the surrender could be taken, up to sixty RIC men arrived in a convoy, sparking a five-hour gun battle, in which eight RIC men were killed and 18 wounded. Two Volunteers were also killed and five wounded, and a civilian was fatally shot. The RIC surrendered and were disarmed. Ashe let them go after warning them not to fight against the Irish Republic again. Ashe's men camped at Kilsalaghan near Dublin until they received orders to surrender on Saturday. The Fingal Battalion's tactics during the Rising foreshadowed those of the IRA during the War of Independence that followed.

Volunteer contingents also mobilised nearby in counties Meath and Louth but proved unable to link up with the North Dublin unit until after it had surrendered. In County Louth, Volunteers shot dead an RIC man near the village of Castlebellingham on 24 April, in an incident in which 15 RIC men were also taken prisoner.

Enniscorthy
In County Wexford, 100–200 Volunteers—led by Robert Brennan, Séamus Doyle and Seán Etchingham—took over the town of Enniscorthy on Thursday 27 April until Sunday. Volunteer officer Paul Galligan had cycled 200 km from rebel headquarters in Dublin with orders to mobilise. They blocked all roads into the town and made a brief attack on the RIC barracks, but chose to blockade it rather than attempt to capture it. They flew the tricolour over the Athenaeum building, which they had made their headquarters, and paraded uniformed in the streets. They also occupied Vinegar Hill, where the United Irishmen had made a last stand in the 1798 rebellion. The public largely supported the rebels and many local men offered to join them.

By Saturday, up to 1,000 rebels had been mobilised, and a detachment was sent to occupy the nearby village of Ferns. In Wexford, the British assembled a column of 1,000 soldiers (including the Connaught Rangers ), two field guns and a 4.7 inch naval gun on a makeshift armoured train. On Sunday, the British sent messengers to Enniscorthy, informing the rebels of Pearse's surrender order. However, the Volunteer officers were sceptical. Two of them were escorted by the British to Arbour Hill Prison, where Pearse confirmed the surrender order.

Galway
In County Galway, 600–700 Volunteers mobilised on Tuesday under Liam Mellows. His plan was to "bottle up the British garrison and divert the British from concentrating on Dublin". However, his men were poorly armed, with only 25 rifles, 60 revolvers, 300 shotguns and some homemade grenades – many of them only had pikes. Most of the action took place in a rural area to the east of Galway city. They made unsuccessful attacks on the RIC barracks at Clarinbridge and Oranmore, captured several officers, and bombed a bridge and railway line, before taking up position near Athenry. There was also a skirmish between rebels and an RIC mobile patrol at Carnmore crossroads. A constable, Patrick Whelan, was shot dead after he had called to the rebels: "Surrender, boys, I know ye all".

On Wednesday, HMS Laburnum arrived in Galway Bay and shelled the countryside on the northeastern edge of Galway. The rebels retreated southeast to Moyode, an abandoned country house and estate. From here they set up lookout posts and sent out scouting parties. On Friday, HMS Gloucester (1909) landed 200 Royal Marines and began shelling the countryside near the rebel position. The rebels retreated further south to Limepark, another abandoned country house. Deeming the situation to be hopeless, they dispersed on Saturday morning. Many went home and were arrested following the Rising, while others, including Mellows, went "on the run". By the time British reinforcements arrived in the west, the Rising there had already disintegrated.

Limerick and Clare
In County Limerick, 300 Irish Volunteers assembled at Glenquin Castle near Killeedy, but they did not take any military action.

In County Clare, Micheal Brennan marched with 100 Volunteers (from Meelick, Oatfield, and Cratloe) to the River Shannon on Easter Monday to await orders from the Rising leaders in Dublin, and weapons from the expected Casement shipment. However, neither arrived and no actions were taken.

Casualties
The Easter Rising resulted in at least 485 deaths, according to the Glasnevin Trust. Of those killed:
 * 260 (about 54%) were civilians
 * 126 (about 26%) were U.K. forces (120 U.K. military personnel, 5 Volunteer Training Corps members, and one Canadian soldier)
 * 35 – Irish Regiments:-
 * 11 – Royal Dublin Fusiliers
 * 10 – Royal Irish Rifles
 * 9 – Royal Irish Regiment
 * 2 – Royal Inniskilling Fusiliers
 * 2 – Royal Irish Fusiliers
 * 1 – Leinster Regiment
 * 74 – British Regiments:-
 * 29 – Sherwood Foresters
 * 15 – South Staffordshire
 * 2 – North Staffordshire
 * 1 – Royal Field Artillery
 * 4 – Royal Engineers
 * 5 – Army Service Corps
 * 10 – Lancers
 * 7 – 8th Hussars
 * 2 – 2nd King Edwards Horse
 * 3 – Yeomanry
 * 1 – Royal Navy
 * 82 (about 16%) were Irish rebel forces (64 Irish Volunteers, 15 Irish Citizen Army and 3 Fianna Éireann)
 * 17 (about 4%) were police
 * 14 – Royal Irish Constabulary
 * 3 – Dublin Metropolitan Police

More than 2,600 were wounded; including at least 2,200 civilians and rebels, at least 370 British soldiers and 29 policemen. All 16 police fatalities and 22 of the British soldiers killed were Irishmen. About 40 of those killed were children (under 17 years old), four of whom were members of the rebel forces.

The number of casualties each day steadily rose, with 55 killed on Monday and 78 killed on Saturday. The British Army suffered their biggest losses in the Battle of Mount Street Bridge on Wednesday when at least 30 soldiers were killed. The rebels also suffered their biggest losses on that day. The RIC suffered most of their casualties in the Battle of Ashbourne on Friday.

The majority of the casualties, both killed and wounded, were civilians. Most of the civilian casualties and most of the casualties overall were caused by the British Army. This was due to the British using artillery, incendiary shells and heavy machine guns in built-up areas, as well as their "inability to discern rebels from civilians". One Royal Irish Regiment officer recalled, "they regarded, not unreasonably, every one they saw as an enemy, and fired at anything that moved". Many other civilians were killed when caught in the crossfire. Both sides, British and rebel, also shot civilians deliberately on occasion; for not obeying orders (such as to stop at checkpoints), for assaulting or attempting to hinder them, and for looting. There were also instances of British troops killing unarmed civilians out of revenge or frustration: notably in the North King Street Massacre, where fifteen were killed, and at Portobello Barracks, where six were shot. Furthermore, there were incidents of friendly fire. On 29 April, the Royal Dublin Fusiliers under Company Quartermaster Sergeant Robert Flood shot dead two British officers and two Irish civilian employees of the Guinness Brewery after he decided they were rebels. Flood was court-martialled for murder but acquitted.

According to the historian Fearghal McGarry, the rebels attempted to avoid needless bloodshed. Desmond Ryan stated that Volunteers were told "no firing was to take place except under orders or to repel attack". Aside from the engagement at Ashbourne, policemen and unarmed soldiers were not systematically targeted, and a large group of policemen was allowed to stand at Nelson's Pillar throughout Monday. McGarry writes that the Irish Citizen Army "were more ruthless than Volunteers when it came to shooting policemen" and attributes this to the "acrimonious legacy" of the Dublin Lock-out.

The vast majority of the Irish casualties were buried in Glasnevin Cemetery in the aftermath of the fighting. British families came to Dublin Castle in May 1916 to reclaim the bodies of British soldiers, and funerals were arranged. Soldiers whose bodies were not claimed were given military funerals in Grangegorman Military Cemetery.

Arrests and executions
In the immediate aftermath, the Rising was commonly described as the "Sinn Féin Rebellion",  reflecting a popular belief that Sinn Féin, a separatist organisation that was neither militant nor republican, was behind it. General Maxwell, for example, signalled his intention "to arrest all dangerous Sinn Feiners", including "those who have taken an active part in the movement although not in the present rebellion".

A total of 3,430 men and 79 women were arrested, including 425 people for looting – roughly, 1,500 of these arrests accounted for the rebels. Detainees were overwhelmingly young, Catholic and religious. 1,424 men and 73 women were released after a few weeks of imprisonment; those interned without trial in England and Wales (see below) were released on Christmas Eve, 1916; the remaining majority of convicts were held until June 1917.

A series of courts martial began on 2 May, in which 187 people were tried. Controversially, Maxwell decided that the courts martial would be held in secret and without a defence, which Crown law officers later ruled to have been illegal. Some of those who conducted the trials had commanded British troops involved in suppressing the Rising, a conflict of interest that the Military Manual prohibited. Only one of those tried by courts martial was a woman, Constance Markievicz, who was also the only woman to be kept in solitary confinement. Ninety were sentenced to death. Fifteen of those (including all seven signatories of the Proclamation) had their sentences confirmed by Maxwell and fourteen were executed by firing squad at Kilmainham Gaol between 3 and 12 May.

Maxwell stated that only the "ringleaders" and those proven to have committed "cold-blooded murder" would be executed. However, some of those executed were not leaders and did not kill anyone, such as Willie Pearse and John MacBride; Thomas Kent did not come out at all—he was executed for the killing of a police officer during the raid on his house the week after the Rising. The most prominent leader to escape execution was Éamon de Valera, Commandant of the 3rd Battalion, who did so partly because of his American birth. Hobson went into hiding, re-emerging after the June amnesty, largely to scorn.

Most of the executions took place over a ten-day period:
 * 3 May: Patrick Pearse, Thomas MacDonagh and Thomas Clarke
 * 4 May: Joseph Plunkett, William Pearse, Edward Daly and Michael O'Hanrahan
 * 5 May: John MacBride
 * 8 May: Éamonn Ceannt, Michael Mallin, Seán Heuston and Con Colbert
 * 12 May: James Connolly and Seán Mac Diarmada

The arrests greatly affected hundreds of families and communities; anti-English sentiment developed among the public, as separatists declared the arrests as indicative of a draconian approach. The public, at large, feared that the response was "an assault on the entirety of the Irish national cause". This radical transformation was recognised in the moment and had become a point of concern among British authorities; after Connolly's execution, the remaining death sentences were commuted to penal servitude. Growing support for republicanism can be found as early as June 1916; imprisonment largely failed to deter militants – interned rebels would proceed to fight at higher rates than those who weren't – who thereafter quickly reorganised the movement.

Frongoch prison camp
Under Regulation 14B of the Defence of the Realm Act 1914 1,836 men were interned at internment camps and prisons in England and Wales. As urban areas were becoming the nexus for republicanism, Internees were largely from such areas. Many Internees had not taken part in the Rising; many thereafter became sympathetic to the nationalist cause.

Internees occupied themselves with the likes of lectures, craftwork, music and sports. These activities – which included games of Gaelic football, crafting of Gaelic symbols, and lessons in Irish – regularly had a nationalist character and the cause itself developed a sense of cohesion within the camps. The military studies included discussion of the Rising. Internment lasted until December of that year with releases having started in July. Martial law had ceased by the end of November.

Casement was tried in London for high treason and hanged at Pentonville Prison on 3 August.

British atrocities
On Tuesday 25 April, Dubliner Francis Sheehy-Skeffington, a pacifist nationalist activist, was arrested and then taken as hostage and human shield by Captain John Bowen-Colthurst; that night Bowen-Colthurst shot dead a teenage boy. Skeffington was executed the next day – alongside two journalists. Two hours later, Bowen-Colthurst captured the Labour Party councillor and IRB lieutenant, Richard O'Carroll and had him shot in the street. Major Sir Francis Vane raised concerns over Bowen-Colthurst's actions and saw to him being court martialled. Bowen-Colthurst was found guilty but insane and was sentenced to an insane asylum. Owing to political pressure, an inquiry soon transpired, revealing the murders and their cover-up. The killing of Skeffington and others provoked outrage among citizens.

The other incident was the "North King Street Massacre". On the night of 28–29 April, British soldiers of the South Staffordshire Regiment, under Colonel Henry Taylor, had burst into houses on North King Street and killed fifteen male civilians whom they accused of being rebels. The soldiers shot or bayoneted the victims, and then secretly buried some of them in cellars or backyards after robbing them. The area saw some of the fiercest fighting of the Rising and the British had taken heavy casualties for little gain. Maxwell attempted to excuse the killings and argued that the rebels were ultimately responsible. He claimed that "the rebels wore no uniform" and that the people of North King Street were rebel sympathisers. Maxwell concluded that such incidents "are absolutely unavoidable in such a business as this" and that "under the circumstance the troops [...] behaved with the greatest restraint". A private brief, prepared for the Prime Minister, said the soldiers "had orders not to take any prisoners" but took it to mean they were to shoot any suspected rebel. The City Coroner's inquest found that soldiers had killed "unarmed and unoffending" residents. The military court of inquiry ruled that no specific soldiers could be held responsible, and no action was taken.

Inquiry
A Royal Commission was set up to enquire into the causes of the Rising. It began hearings on 18 May under the chairmanship of Lord Hardinge of Penshurst. The Commission heard evidence from Sir Matthew Nathan, Augustine Birrell, Lord Wimborne, Sir Neville Chamberlain (Inspector-General of the Royal Irish Constabulary), General Lovick Friend, Major Ivor Price of Military Intelligence and others. The report, published on 26 June, was critical of the Dublin administration, saying that "Ireland for several years had been administered on the principle that it was safer and more expedient to leave the law in abeyance if collision with any faction of the Irish people could thereby be avoided." Birrell and Nathan had resigned immediately after the Rising. Wimborne resisted the pressure to resign, but was recalled to London by Asquith. He was re-appointed in July 1916. Chamberlain also resigned.

Reaction of the Dublin public
At first, many Dubliners were bewildered by the outbreak of the Rising. James Stephens, who was in Dublin during the week, thought, "None of these people were prepared for Insurrection. The thing had been sprung on them so suddenly they were unable to take sides." Eyewitnesses compared the ruin of Dublin with the destruction of towns in Europe in the war: the physical damage, which included over ninety fires, was largely confined to Sackville Street. In the immediate aftermath, the Irish government was in disarray.

There was great hostility towards the Volunteers in some parts of the city which escalated to physical violence in some instances. Historian Keith Jeffery noted that most of the opposition came from the dependents of British Army personnel. The death and destruction, which resulted in disrupted trade, considerable looting and unemployment, contributed to the antagonism of the Volunteers, who were denounced as "murderers" and "starvers of the people" – the monetary consequences of the Rising were estimated to be at £2,500,000. International aid was supplied to residents – nationalists aided the dependents of Volunteers. The British Government compensated the consequences to the sum of £2,500,000.

Support for the rebels did exist among Dubliners, expressed through both crowds cheering at prisoners and reverent silence. With martial law seeing this expression prosecuted, many would-be supporters elected to remain silent although "a strong undercurrent of disloyalty" was still felt. Drawing upon this support, and amidst the deluge of nationalist ephemera, the significantly popular Catholic Bulletin eulogised Volunteers killed in action and implored readers to donate; entertainment was offered as an extension of those intentions, targeting local sectors to great success. The Bulletin 's Catholic character allowed it to evade the widespread censorship of press and seizure of republican propaganda; it therefore exposed many unaware readers to such propaganda.

Rise of Sinn Féin
A meeting called by Count Plunkett on 19 April 1917 led to the formation of a broad political movement under the banner of Sinn Féin which was formalised at the Sinn Féin Ard Fheis of 25 October 1917. The Conscription Crisis of 1918 further intensified public support for Sinn Féin before the general elections to the British Parliament on 14 December 1918, which resulted in a landslide victory for Sinn Féin, winning 73 seats out of 105, whose Members of Parliament (MPs) gathered in Dublin on 21 January 1919 to form Dáil Éireann and adopt the Declaration of Independence.

During that election, they drew directly upon the Rising and their popularity was significantly accreditable to that association, one that accrued political prestige until the end of the century. Many participants of the Rising would soon assume electoral positions. Sinn Féin served as an alternative to the Irish Parliamentary Party whose support for British establishments alienated voters.

Sinn Féin would become closely aligned with the Irish Republican Army, who sought to continue the IRB's ideals and waged armed conflict against British forces.

Legacy
1916 – containing both the Rising and the Battle of the Somme, events paramount to the memory of Irish Republicans and Ulster Unionists, respectively – had a profound effect on Ireland and is remembered accordingly. The Rising was among the events that ended colonial rule in Ireland, succeeded by the Irish War of Independence. The legacy of the Rising possess many dimensions although the declaration of the Republic and the ensuing executions remain focal points.

Annual parades in celebration of the Rising occurred for many years, however, ceased after The Troubles in Northern Ireland began, being seen as supportive of republican paramilitary violence – the Rising is a common feature of republican murals in Northern Ireland. These commemorations celebrated the Rising as the origin of the Irish state, a stance reiterated through extensive analysis. Unionists contend that the Rising was an illegal attack on the British State that should not be celebrated. Revivalism of the parades has inspired significant public debate, although the centenary of the Rising, which featured the likes of ceremonies and memorials, was largely successful and praised for its sensitivity.

The leaders of the Rising were "instantly apotheosized" and remembrance was situated within a larger republican tradition of claimed martyrdom – the Catholic Church would contend this narrative as the foundational myth of the Irish Free State, assuming a place within the remembrance as an association between republicanism and Catholicism grew. The "Pearsean combination of Catholicism, Gaelicism, and spiritual nationalism" would become dominant within republicanism, the ideas gaining a quasi-religiosity. Within the Free State, the Rising was sanctified by officials, positioned as a "highly disciplined military operation". Historians largely agree that the Rising succeeded by offering a symbolic display of sacrifice, while the military action was a considerable failure. As Monk Gibbon remarked, the "shots from khaki-uniformed firing parties did more to create the Republic of Ireland than any shot fired by a Volunteer in the course of Easter week".

Literature surrounding the Rising was significant: MacDonagh, Plunkett, and Pearse were themselves poets, whose ideals were granted a spiritual dimension in their work; Arnold Bax, Francis Ledwidge, George William Russell and W. B. Yeats responded through verse that ranged from endorsement to elegies. Although James Joyce was ambivalent to the insurgence, metaphors of and imagery consistent with the Rising appear in his later work. Hugh Leonard, Denis Johnston, Tom Murphy, Roddy Doyle and Sorley MacLean are among writers would later invoke the Rising. Now extensively dramatised, its theatricality was identified in the moment and has been stressed in its remembrance. Literary and political evocation position the Rising as a "watershed moment" central to Irish history.

Black, Basque, Breton, Catalan and Indian nationalists have drawn upon the Rising and its consequences. For the latter, Jawaharlal Nehru noted, the symbolic display was the appeal, that of the transcendent, "invincible spirit of a nation"; such was broadly appealing in America, where diasporic, occasionally socialist, nationalism occurred. Vladimir Lenin was effusive, ascribing its anti-imperialism a singular significance within geopolitics – his only misgiving was its estrangement from the broader wave of revolution occurring.

During the Troubles, significant revisionism of the Rising occurred. Revisionists contended that it was not a "heroic drama" as thought but rather informed the violence transpiring, by having legitimised a "cult of 'blood sacrifice'". With the advent of a Provisional IRA ceasefire and the beginning of what became known as the Peace Process during the 1990s, the government's view of the Rising grew more positive and in 1996 an 80th anniversary commemoration at the Garden of Remembrance in Dublin was attended by the Taoiseach and leader of Fine Gael, John Bruton.

In popular culture

 * "Easter, 1916", a poem by the poet and playwright W.B. Yeats, published in 1921.
 * "The Foggy Dew" is a song by Canon Charles O'Neill, composed during the Irish War of Independence, that eulogises the rebels of the Easter Rising.
 * The Plough and the Stars is a 1926 play by Seán O'Casey that takes place during the Easter Rising.
 * Insurrection is a 1950 novel by Liam O'Flaherty that takes place during the Rising.
 * The Red and the Green is a 1965 novel by Iris Murdoch that covers the events leading up to and during the Easter Rising.
 * Insurrection is an eight-part 1966 docudrama made by Telefís Éireann for the 50th anniversary of the Rising. It was rebroadcast during the centenary celebrations in 2016.
 * "Grace" is a 1985 song about the marriage of Joseph Plunkett to Grace Gifford in Kilmainham Gaol before his execution.
 * 1916, A Novel of the Irish Rebellion is a 1998 historical novel by Morgan Llywelyn.
 * A Star Called Henry is a 1999 novel by Roddy Doyle that partly recounts the Easter Rising through the involvement of the novel's protagonist Henry Smart.
 * At Swim, Two Boys is a 2001 novel by Irish writer Jamie O'Neill, set in Dublin before and during the 1916 Easter Rising.
 * Rebel Heart, is a 2001 BBC miniseries on the life of a (fictional) nationalist from the Rising through the Irish Civil War.
 * Blood Upon the Rose is a 2009 graphic novel by Gerry Hunt depicting the events of the Easter Rising.
 * 1916 Seachtar na Cásca is a 2010 Irish TV documentary series based on the Easter Rising, telling about seven signatories of the rebellion.
 * The Dream of the Celt is a 2012 novel by Mario Vargas Llosa based on the life and death of Roger Casement, including his involvement with the Rising.
 * Rebellion is a 2016 mini-series about the Easter Rising.
 * 1916 is a 2016 three-part documentary mini-series about the Easter Rising narrated by Liam Neeson.
 * Penance is a 2018 Irish film set primarily in Donegal in 1916 and in Derry in 1969, in which the Rising is also featured.

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

title: Easter Rising


text:
Eschrichtiidae

Eschrichtiidae or the gray whales is a family of baleen whale (Parvorder Mysticeti) with a single extant species, the gray whale (Eschrichtius robustus), as well as three described fossil genera: Archaeschrichtius and Eschrichtioides from the Miocene and Pliocene of Italy respectively, and Gricetoides from the Pliocene of North Carolina. More recent phylogenetic studies have found this family to be invalid, with its members nesting inside the Balaenopteridae. The names of the extant genus and the family honours Danish zoologist Daniel Eschricht.

Taxonomy
In his morphological analysis, found that eschrichtiids and Cetotheriidae (Cetotherium, Mixocetus and Metopocetus) form a monophyletic sister group of Balaenopteridae.

A specimen from the Late Pliocene of northern Italy, named "Cetotherium" gastaldii by and renamed "Balaenoptera" gastaldii by, was identified as a basal eschrichtiid by  who recombined it to Eschrichtioides gastaldii.

found that the gray whale is phylogenetically distinct from rorquals and that previous morphological studies were correct in the conclusion that the evolution of gulp feeding was a single event in the rorqual lineage. In contrast, multiple later studies found the gray whale to fall within the family Balaenopteridae, being more derived than the minke whales but basal to all other members in the family, and reclassified it in Balaenopteridae; the American Society of Mammalogists has followed this classification.

Evolution
Fossils of Eschrichtiidae have been found in all major oceanic basins in the Northern Hemisphere, and the family is believed date back to the Late Miocene. Today, gray whales are only present in the northern Pacific, but a population was also present in the northern Atlantic before being driven to extinction by European whalers three centuries ago.

Fossil eschrichtiids from before the Holocene are rare compared to other fossil mysticetes. The only Pleistocene fossil from the Pacific referred to E. eschrichtius is a partial skeleton and an associated skull from California, estimated to be about 200 thousand years old. However, a late Pliocene fossil from Hokkaido, Japan, referred to Eschrichtius sp. is estimated to be and a similar unnamed fossil has been reported from California.

In their description of Archaeschrichtius ruggieroi from the late Miocene of Italy, argued that eschrichtiids most likely originated in the Mediterranean Basin about  and remained there, either permanently or intermittently, at least until the Early Pliocene (5–3 Mya), (but see Messinian salinity crisis.)

title: Eschrichtiidae