Andromeda Galaxy

The Andromeda Galaxy with satellite galaxies M32 (center left above the galactic nucleus) and M110 (center left below the galaxy)
Great Andromeda "Nebula" (M110 to upper left), as photographed by Isaac Roberts, 1899.
Location of the Andromeda Galaxy (M31) in the Andromeda constellation.
Andromeda Galaxy near upper-left of the Very Large Telescope. The Triangulum Galaxy is visible on the top.
The Andromeda Galaxy as seen by NASA's Wide-field Infrared Survey Explorer.
The Andromeda Galaxy pictured in ultraviolet by GALEX (2003).
Illustration showing both the size of each galaxy and the distance between the two galaxies, to scale.
Giant halo around Andromeda Galaxy.
The Andromeda Galaxy (M110 below) seen in infrared by the Spitzer Space Telescope, one of NASA's four Great Space Observatories.
Image of the Andromeda Galaxy taken by Spitzer in infrared, 24 micrometres (Credit:NASA/JPL–Caltech/Karl D. Gordon, University of Arizona).
A Galaxy Evolution Explorer image of the Andromeda Galaxy. The bands of blue-white making up the galaxy's striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. When observed in visible light, the Andromeda Galaxy's rings look more like spiral arms. The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA's Spitzer Space Telescope. Astronomers using the latter interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago.
Hubble image of the Andromeda Galaxy core showing possible double structure. NASA/ESA photo.
Artist's concept of the Andromeda Galaxy's core, showing a view across a disk of young, blue stars encircling a supermassive black hole. NASA/ESA photo.
Chandra X-ray telescope image of the center of the Andromeda Galaxy. A number of X-ray sources, likely X-ray binary stars, within the galaxy's central region appear as yellowish dots. The blue source at the center is at the position of the supermassive black hole.
The Andromeda Galaxy in high-energy X-ray and ultraviolet light (released 5 January 2016).
Star clusters in the Andromeda Galaxy.
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Barred spiral galaxy with diameter of about 220,000 ly approximately 2.5 e6ly from Earth and the nearest large galaxy to the Milky Way.

- Andromeda Galaxy
The Andromeda Galaxy with satellite galaxies M32 (center left above the galactic nucleus) and M110 (center left below the galaxy)

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Johannes Hevelius's depiction of Andromeda, from the 1690 edition of his Uranographia. As was conventional for celestial atlases of the time, the constellation is a mirror image of modern maps as it was drawn from a perspective outside the celestial sphere.

Andromeda (constellation)

One of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy, and one of the 88 modern constellations.

One of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy, and one of the 88 modern constellations.

Johannes Hevelius's depiction of Andromeda, from the 1690 edition of his Uranographia. As was conventional for celestial atlases of the time, the constellation is a mirror image of modern maps as it was drawn from a perspective outside the celestial sphere.
Andromeda as depicted in Urania's Mirror, a set of constellation cards published in London c. 1825, showing the constellation from the inside of the celestial sphere
Andromeda depicted in an early scientific manuscript, c.1000
Photo of the constellation Andromeda, as it appears to the naked eye. Lines have been added for clarity.
Andromeda as it appears in the night sky, with the superimposed figure.
A Hertzsprung-Russel diagram for stars brighter than 4th magnitude in the constellation Andromeda (axes not labelled).
M31, the Great Galaxy of Andromeda.
Sharp view of the Andromeda Galaxy
The Blue Snowball Nebula as seen through the Hubble Space Telescope.

The constellation's most obvious deep-sky object is the naked-eye Andromeda Galaxy (M31, also called the Great Galaxy of Andromeda), the closest spiral galaxy to the Milky Way and one of the brightest Messier objects.

All Messier objects, photographed by an amateur astronomer

Messier object

The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his Catalogue des Nébuleuses et des Amas d'Étoiles (Catalogue of Nebulae and Star Clusters).

The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his Catalogue des Nébuleuses et des Amas d'Étoiles (Catalogue of Nebulae and Star Clusters).

All Messier objects, photographed by an amateur astronomer
Charles Messier
Star chart depicting the Messier objects plotted on a rectangular grid representing right ascension and declination

For example, Messier 1 is a supernova remnant, known as the Crab Nebula, and the great spiral Andromeda Galaxy is M31.

The "Pillars of Creation" from the Eagle Nebula. Evidence from the Spitzer Space Telescope suggests that the pillars may already have been destroyed by a supernova explosion, but the light showing us the destruction will not reach the Earth for another millennium.

Nebula

Distinct body of interstellar clouds (which can consist of cosmic dust, hydrogen, helium, molecular clouds; possibly as ionized gases).

Distinct body of interstellar clouds (which can consist of cosmic dust, hydrogen, helium, molecular clouds; possibly as ionized gases).

The "Pillars of Creation" from the Eagle Nebula. Evidence from the Spitzer Space Telescope suggests that the pillars may already have been destroyed by a supernova explosion, but the light showing us the destruction will not reach the Earth for another millennium.
Portion of the Carina Nebula
NGC 604, a nebula in the Triangulum Galaxy
The Carina Nebula is an example of a diffuse nebula
The Oyster Nebula is a planetary nebula located in the constellation of Camelopardalis
The Westbrook Nebula is an example of a protoplanetary nebula located in the constellation of Auriga
The Crab Nebula, an example of a supernova remnant
Close up on the Orion Arm, with major stellar associations (yellow), nebulae (red) and dark nebulae (grey) around the Local Bubble.
Herbig–Haro HH 161 and HH 164.<ref>{{cite news|title=A stellar sneezing fit|url=http://www.spacetelescope.org/images/potw1350a/|access-date=16 December 2013|newspaper=ESA/Hubble Picture of the Week}}</ref>
The Omega Nebula, an example of an emission nebula
The Horsehead Nebula, an example of a dark nebula.
The Cat's Eye Nebula, an example of a planetary nebula.
The Red Rectangle Nebula, an example of a protoplanetary nebula.
The delicate shell of SNR B0509-67.5
Tycho Supernova remnant in X-ray light

The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.

The naked eye

Naked eye

Practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection.

Practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection.

The naked eye
A photographic approximation of a naked eye view of the night sky from a small rural town (top) and a metropolitan area (bottom). Light pollution dramatically reduces the visibility of stars.
The Milky Way is visible over the Very Large Telescope, demonstrating clear atmosphere above Paranal Observatory.

These include the Pleiades, h/χ Persei, the Andromeda Galaxy, the Carina Nebula, the Orion Nebula, Omega Centauri, 47 Tucanae, the Ptolemy Cluster Messier 7 near the tail of Scorpius and the globular cluster M13 in Hercules.

The giant elliptical galaxy ESO 325-G004

Elliptical galaxy

Type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image.

Type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image.

The giant elliptical galaxy ESO 325-G004
Elliptical galaxy IC 2006.
The central galaxy in this image is a gigantic elliptical galaxy designated 4C 73.08.
The brilliant central object is a supergiant elliptical galaxy, the dominant member of a galaxy cluster with the name MACSJ1423.8+2404. Note the gravitational lensing.
NGC 3597 is the product of a collision between two galaxies. It is evolving into a giant elliptical galaxy.

The Milky Way galaxy, depending upon an unknown tangential component, is on a four- to five-billion-year collision course with the Andromeda Galaxy.

RS Puppis, one of the brightest known Cepheid variable stars in the Milky Way galaxy ( Hubble Space Telescope )

Cepheid variable

Type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

Type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

RS Puppis, one of the brightest known Cepheid variable stars in the Milky Way galaxy ( Hubble Space Telescope )
The period-luminosity curves of classic and type II Cepheids
Illustration of Cepheid variables (red dots) at the center of the Milky Way
Light curve of Delta Cephei, the prototype of classical cepheids, showing the regular variations produced by intrinsic stellar pulsations
Light curve of κ Pavonis, a Type II cepheid, recorded by NASA's Transiting Exoplanet Survey Satellite (TESS)
Time lapse of the Cepheid type variable star Polaris illustrating the visual appearance of its cycle of brightness changes.

In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the "Andromeda Nebula" and showed that those variables were not members of the Milky Way.

Artist's conception of a white dwarf, right, accreting hydrogen from the Roche lobe of its larger companion star

Nova

Transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova, which is Latin for "new") that slowly fades over weeks or months. Causes of the dramatic appearance of a nova vary, depending on the circumstances of the two progenitor stars. All observed novae involve white dwarfs in close binary systems. The main sub-classes of novae are classical novae, recurrent novae (RNe), and dwarf novae. They are all considered to be cataclysmic variable stars.

Transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova, which is Latin for "new") that slowly fades over weeks or months. Causes of the dramatic appearance of a nova vary, depending on the circumstances of the two progenitor stars. All observed novae involve white dwarfs in close binary systems. The main sub-classes of novae are classical novae, recurrent novae (RNe), and dwarf novae. They are all considered to be cataclysmic variable stars.

Artist's conception of a white dwarf, right, accreting hydrogen from the Roche lobe of its larger companion star
Nova Eridani 2009 (apparent magnitude ~8.4)
GK Persei: Nova of 1901
Nova in Andromeda Galaxy

Roughly 25 novae brighter than about the twentieth magnitude are discovered in the Andromeda Galaxy each year and smaller numbers are seen in other nearby galaxies.

SN 1994D (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526

Supernova

A supernova ( or supernovas; abbr.

A supernova ( or supernovas; abbr.

SN 1994D (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526
SN Antikythera in galaxy cluster RXC J0949.8+1707. SN Eleanor and SN Alexander were observed in the same galaxy in 2011.
Supernova remnant SNR E0519-69.0 in the Large Magellanic Cloud
"A star set to explode", the SBW1 nebula surrounds a massive blue supergiant in the Carina Nebula.
Multi-wavelength X-ray, infrared, and optical compilation image of Kepler's supernova remnant, SN 1604
Light curve for type Ia SN 2018gv
Light curves are used to classify type II-P and type II-L supernovae.
Artist's impression of supernova 1993J
In the galaxy NGC 1365 a supernova (the bright dot slightly above the galactic center) rapidly brightens, then fades more slowly.
Formation of a type Ia supernova
The layers of a massive, evolved star just before core collapse (not to scale)
Supernova types by initial mass-metallicity
Remnants of single massive stars
Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming an iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated by a process that may include neutrino interaction. The surrounding material is blasted away (f), leaving only a degenerate remnant.
The atypical subluminous type II SN 1997D
SN 2008D, a type Ib supernova at the far upper end of the galaxy, shown in X-ray (left) and visible light (right)
Comparative supernova type light curves
Messier 61 with supernova SN2020jfo, taken by an amateur astronomer in 2020
The pulsar in the Crab Nebula is travelling at 375 km/s relative to the nebula.
The radioactive decays of nickel-56 and cobalt-56 that produce a supernova visible light curve
Isolated neutron star in the Small Magellanic Cloud
Periodic table showing the source of each element in the interstellar medium
Supernova remnant N 63A lies within a clumpy region of gas and dust in the Large Magellanic Cloud
The nebula around Wolf–Rayet star WR124, which is located at a distance of about 21,000 light-years

The first such observation was of SN 1885A in the Andromeda Galaxy.

Local Group of galaxies, including the massive members Messier 31 (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.

Local Group

Galaxy group that includes the Milky Way.

Galaxy group that includes the Milky Way.

Local Group of galaxies, including the massive members Messier 31 (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies.
Distribution of the iron content (in logarithmic scale) in four neighbouring dwarf galaxies of the Milky Way

It consists of two collections of galaxies in a "dumbbell" shape: the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other.

Portrait by John Collier, 1905

William Huggins

English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife, Margaret.

English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife, Margaret.

Portrait by John Collier, 1905
William Huggins (1910)
Caricature of Huggins by Leslie Ward in Vanity Fair

He was also the first to distinguish between nebulae and galaxies by showing that some (like the Orion Nebula) had pure emission spectra characteristic of gas, while others like the Andromeda Galaxy had the spectral characteristics of stars.