Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a spiral galaxy about 12 million light-years away, with a diameter of 90,000 light years, about half the size of the Milky Way, in the constellation Ursa Major. Due to its proximity to Earth, large size, and active galactic nucleus (which harbors a 70 million M☉ supermassive black hole), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers.
Messier 81 was first discovered by Johann Elert Bode on December 31, 1774. Consequently, the galaxy is sometimes referred to as "Bode's Galaxy". In 1779, Pierre Méchain and Charles Messier reidentified Bode's object, which was subsequently listed in the Messier Catalogue. Messier 81 is located approximately 10° northwest of Alpha Ursae Majoris along with several other galaxies in the Messier 81 Group.
Messier 81 and Messier 82 can both be viewed easily using binoculars and small telescopes. The two objects are generally not observable to the unaided eye, although highly experienced amateur astronomers may be able to see Messier 81 under exceptional observing conditions with a very dark sky. Telescopes with apertures of 8 inches (20 cm) or larger are needed to distinguish structures in the galaxy. Its far northern declination makes it generally visible for observers in the northern hemisphere. It is not visible to most observers in the southern hemisphere, except those in a narrow latitude range immediately south of the equator.
Most of the emission at infrared wavelengths originates from interstellar dust. This interstellar dust is found primarily within the galaxy's spiral arms, and it has been shown to be associated with star formation regions. The general explanation is that the hot, short-lived blue stars that are found within star formation regions are very effective at heating the dust and thus enhancing the infrared dust emission from these regions.
Only one supernova has been detected in Messier 81. The supernova, named SN 1993J, was discovered on 28 March 1993 by F. García in Spain. At the time, it was the second brightest supernova observed in the 20th century. The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernova formed by the explosion of a giant star) with strong hydrogen spectral line emission, but later the hydrogen lines faded and strong helium spectral lines appeared, making the supernova look more like a type Ib.
Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernova but did resemble the variations observed in type Ib supernovae. Hence, the supernova has been classified as a type IIb, a transitory class between type II and type Ib. The scientific results from this supernova suggested that type Ib and Ic supernovae were actually formed through the explosions of giant stars through processes similar to those taking place in type II supernovae. The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81. As a local galaxy, the Central Bureau for Astronomical Telegrams (CBAT) tracks novae in M81 along with M31 and M33.
Messier 81 is the largest galaxy in the M81 Group, a group of 34 galaxies located in the constellation Ursa Major. At approximately 11.7 Mly (3.6 Mpc) from the Earth, it makes this group and the Local Group, containing the Milky Way, relative neighbors in the Virgo Supercluster.
Gravitational interactions of M81 with M82 and NGC 3077 have stripped hydrogen gas away from all three galaxies, forming gaseous filamentary structures in the group. Moreover, these interactions have allowed interstellar gas to fall into the centers of M82 and NGC 3077, leading to vigorous star formation or starburst activity there.
M81 with satellite galaxy Holmberg IX in the top center-right corner
|Observation data (J2000 epoch)|
|Right ascension||09h 55m 33.2s|
|Declination||+69° 3′ 55″|
|Helio radial velocity||−34|
|Apparent magnitude (V)||6.94|
|Apparent size (V)||26.9 × 14.1 moa|
|NGC 3031, UGC 5318, MCG+12-10-010, PGC 28630, Bode's Galaxy|
1774 in science
The year 1774 in science and technology involved some significant events.Apparent magnitude
The apparent magnitude (m) of an astronomical object is a number that is a measure of its brightness as seen by an observer on Earth. The magnitude scale is logarithmic. A difference of 1 in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The brighter an object appears, the lower its magnitude value (i.e. inverse relation), with the brightest astronomical objects having negative apparent magnitudes: for example Sirius at −1.46.
The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry. Apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is usually measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V ("visual") filter band would be denoted either as mV or often simply as V, as in "mV = 15" or "V = 15" to describe a 15th-magnitude object.Bulge (astronomy)
In astronomy, a bulge is a tightly packed group of stars within a larger formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies (see galactic spheroid). Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy. It is now thought that there are at least two types of bulges: bulges that are like ellipticals and bulges that are like spiral galaxies.Grand design spiral galaxy
A grand design spiral galaxy is a type of spiral galaxy with prominent and well-defined spiral arms, as opposed to multi-arm and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy extend clearly around the galaxy through many radians and can be observed over a large fraction of the galaxy's radius. As of 2002, approximately 10 percent of all currently known spiral galaxies are classified as grand design type spirals, including M81, M51, M74, M100, and M101.List of black holes
This is a list of black holes (and stars considered probable candidates) organized by size (including black holes of undetermined mass); some items in this list are galaxies or star clusters that are believed to be organized around a black hole. Messier and New General Catalogue designations are given where possible.List of galaxies
The following is a list of notable galaxies.
There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in our Local Supercluster and an estimated number of about one to two trillion in all of the observable universe.
The discovery of the nature of galaxies as distinct from other nebulae (interstellar clouds) was made in the 1920s. The first attempts at systematic catalogues of galaxies were made in the 1960s, with the Catalogue of Galaxies and Clusters of Galaxies listing 29,418 galaxies and galaxy clusters, and with the Morphological Catalogue of Galaxies, a putatively complete list of galaxies with photographic magnitude above 15, listing 30,642. In the 1980s, the Lyons Groups of Galaxies listed 485 galaxy groups with 3,933 member galaxies. Galaxy Zoo is a project aiming at a more comprehensive list: launched in July 2007, it has classified over one million galaxy images from The Sloan Digital Sky Survey, The Hubble Space Telescope and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey.There is no universal naming convention for galaxies, as they are mostly catalogued before it is established whether the object is or isn't a galaxy. Mostly they are identified by their celestial coordinates together with the name of the observing project (HUDF, SDSS, 3C, CFHQS, NGC/IC, etc.)List of galaxies named after people
A small number of galaxies or galaxy groups have been named after individual people. In most cases, the named individual was the person who discovered the object, who first brought attention to it, or who first studied it scientifically.
Many of the brighter galaxies visible from the Northern Hemisphere have Messier numbers, named after Charles Messier. For instance, the Andromeda Galaxy is Messier 31 and the Whirlpool Galaxy is Messier 51. There are a few other comprehensive catalogs that assign the cataloguer's name to galaxies. For instance, Markarian galaxies, named after Benjamin Markarian, are galaxies with excess blue and ultraviolet emission; galaxies in the Atlas of Peculiar Galaxies are assigned an Arp number after Halton Arp who produced the catalog; etc. Objects in these catalogs are excluded below, except in cases where they carry the name of an additional person.List of novae in 2018
The following is a list of all novae that are known to have occurred in 2018. A nova is an energetic astronomical event caused by a white dwarf accreting matter from a star it is orbiting (typically a red giant, whose outer layers are more weakly attached than smaller, denser stars) Alternatively, novae can rarely be caused by a pair of stars merging with each other, however such events are vastly less common than novae caused by white dwarves.
In 2018, 15 novae were discovered in the Milky Way, 14 being classical novae, and 1 being a dwarf nova of a previously known variable star, V392 Persei, which was discovered in 1972. An additional 23 novae were discovered in the Andromeda Galaxy, 8 in Messier 81, 1 in the Triangulum Galaxy, and 1 in Messier 83.M81
M81 or M-81 may refer to:
M-81 (Michigan highway), a state highway in Michigan
Messier 81, a spiral galaxy in the constellation Ursa Major, also known as NGC 3031 or Bode's Galaxy
U.S. Woodland, a camouflage pattern also known as "M81"M81 Group
The M81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightnesses. The approximate center of the group is located at a distance of 3.6 Mpc, making it one of the nearest groups to the Local Group. The group is estimated to have a total mass of (1.03 ± 0.17)×1012M☉.
The M81 Group, the Local Group, and other nearby groups all lie within the Virgo Supercluster (i.e. the Local Supercluster).NGC 3738
NGC 3738 is a dwarf galaxy in the constellation of Ursa Major and belongs to the Messier 81 group of galaxies. NGC 3738 is 12 million light-years from the sun. The galaxy was first discovered by astronomer William Herschel in 1789. NGC 3738 is a blue compact dwarf, which is small compared to large spiral galaxies. The galaxy is about 10,000 light-years across. It is one-tenth the size of the Milky Way Blue compact dwarf galaxies are blue in appearance because of the large cluster of hot massive stars. The galaxies are relatively dim and appear to be irregular in shape. They are typically chaotic in appearance.NGC 4236
NGC 4236 (also known as Caldwell 3) is a barred spiral galaxy located in the constellation Draco.
The galaxy is a member of the M81 Group, a group of galaxies located at a distance of approximately 11.7 Mly (3.6 Mpc) from Earth. The group also contains the spiral galaxy Messier 81 and the starburst galaxy Messier 82. NGC 4236 is located away from the central part of the M81 group at a distance of is 14.5 Mly (4.45 Mpc) from Earth.Naked eye
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying or light-collecting optical instrument, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is still considered "naked".
In astronomy, the naked eye may be used to observe celestial events and objects visible without equipment, such as conjunctions, passing comets, meteor showers, and the brightest asteroids, including 4 Vesta. Sky lore and various tests demonstrate an impressive variety of phenomena visible to the unaided eye.SN 1993J
SN 1993J is a supernova observed in the galaxy M81. It was discovered on 28 March 1993 by F. Garcia in Spain. At the time, it was the second-brightest type II supernova observed in the twentieth century behind SN 1987A.The spectral characteristics of the supernova changed over time. Initially, it looked more like a type II supernova (a supernova formed by the explosion of a giant star) with strong hydrogen spectral line emission, but later the hydrogen lines faded and strong helium spectral lines appeared, making the supernova look more like a type Ib. Moreover, the variations in SN 1993J's luminosity over time were not like the variations observed in other type II supernovae but did resemble the variations observed in type Ib supernovae. Hence, the supernova has been classified as a type IIb supernova, an intermediate class between type II and type Ib. The scientific results from this supernova suggested that type Ib and Ic supernovae were actually formed through the explosions of giant stars through processes similar to what takes place in type II supernovae. The supernova was also used to estimate a distance of 8.5 ± 1.3 Mly (2.6 ± 0.4 Mpc) to Messier 81.Light echoes from the explosion have subsequently been detected.
The progenitor of SN 1993J was identified in pre-explosion ground-based images. The progenitor was observed to be a K-type supergiant star, with an excess in the ultraviolet possibly due to surrounding hot stars or a hot binary companion. While the supernova is located in a region populated by young massive stars, late-time photometry with the Hubble Space Telescope and spectroscopy with the Keck 10m-telescope presented by Maund and collaborators revealed the presence of the long-suspected B-supergiant companion star.Triangulum Galaxy
The Triangulum Galaxy is a spiral galaxy approximately 3 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. The Triangulum Galaxy is the third-largest member of the Local Group of galaxies, behind the Milky Way and the Andromeda Galaxy. It is one of the most distant permanent objects that can be viewed with the naked eye.
The galaxy is the smallest spiral galaxy in the Local Group and it is believed to be a satellite of the Andromeda Galaxy due to their interactions, velocities, and proximity to one another in the night sky. It also has an H II nucleus.UGC 5497
UGC 5497 is a dwarf galaxy, located about 12 million light years away in the constellation Ursa Major. It is a member of the M81 Group.Ultraviolet astronomy
Ultraviolet astronomy is the observation of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy and gamma ray astronomy. Ultraviolet light is not visible to the human eye. Most of the light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space.Unbarred spiral galaxy
An unbarred spiral galaxy is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme.
The Sombrero Galaxy is an unbarred spiral galaxy.
Barless spiral galaxies are one of three general types of spiral galaxies under the de Vaucouleurs system classification system, the other two being intermediate spiral galaxy and barred spiral galaxy. Under the Hubble tuning fork, it is one of two general types of spiral galaxy, the other being barred spirals.Ursa Major
Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) she-bear", standing as a reference to and in direct contrast with nearby Ursa Minor, the lesser bear. In antiquity, it was one of the original 48 constellations listed by Ptolemy (2nd century AD), and is now the third largest constellation of the 88 modern constellations.
Ursa Major is primarily known from the asterism of its main seven relatively bright stars comprising the "Big Dipper", "the Wagon", "Charles's Wain" or "the Plough" (among others), with its stellar configuration mimicking the shape of the "Little Dipper".
The general constellation outline often significantly features in numerous world cultures, and frequently is used as a symbol of the north. e.g. as the flag of Alaska. Also the asterism's two brightest stars, named Dubhe and Merak (α Ursae Majoris and β Ursae Majoris), can be used as the navigational pointer towards the place of the current northern pole star, Polaris in Ursa Minor.
Ursa Major is visible throughout the year from most of the northern hemisphere, and appears circumpolar above the mid-northern latitudes. From southern temperate latitudes, the main asterism is invisible, but the southern parts of the constellation can still be viewed.
List of notable Seyfert galaxies