NGC 6822
Encyclopedia
NGC 6822 is a barred irregular galaxy
approximately 1.6 million light-year
s away in the constellation
Sagittarius
. Part of the Local Group
of galaxies, it was discovered by E. E. Barnard in 1881 (hence its name), with a six-inch refractor telescope. It is one of the closer galaxies
to the Milky Way
. It is similar in structure and composition to the Small Magellanic Cloud
.
wrote the seminal paper N.G.C. 6822, A Remote Stellar System wherein he identified 15 variable stars (11 of which were Cepheids). He also surveyed the galaxy's stars distribution down to magnitude 19.4. He provided spectral characteristics, luminosities and dimensions for the five brightest "diffuse nebula" (giant H II region
s) that included the Bubble Nebula
and the Ring Nebula
. He also computed the absolute magnitude
of the entire galaxy.
Hubble's detection of eleven Cepheid variable stars was a milestone in astronomy
. Utilizing the Cepheid Period-Luminosity relationship, Hubble determined a distance of more than 700,000 light-years. This was the first system beyond the Magellanic Clouds to have its distance accurately determined. (Hubble continued this process with the Andromeda Galaxy
and the Triangulum Galaxy
). His distance to the galaxy was way beyond Harlow Shapley
's value of 300,000 light-years for the size of universe. In this paper, Hubble concluded "the Great Debate
" of 1920 between Heber Curtis
and Shapley over the scale of the universe and the nature of the "spiral nebula". It soon became evident that all spiral nebulae were in fact spiral galaxies
far outside our own Milky Way.
In 1977, Paul W. Hodge
extended the list of known H II regions in Barnard to 16. Today, there are over 150 of these regions cataloged in Barnard's Galaxy.
Barred irregular galaxy
A barred irregular galaxy is an irregular version of a barred spiral galaxy. Examples include the Large Magellanic Cloud and NGC 6822. Some barred irregular galaxies may actually be dwarf spiral galaxies, which have been distorted into an irregular shape by tidal interactions with a more massive...
approximately 1.6 million light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
. Part of the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
of galaxies, it was discovered by E. E. Barnard in 1881 (hence its name), with a six-inch refractor telescope. It is one of the closer galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
to the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. It is similar in structure and composition to the Small Magellanic Cloud
Small Magellanic Cloud
The Small Magellanic Cloud is a dwarf galaxy. It has a diameter of about 7,000 light-years and contains several hundred million stars. It has a total mass of approximately 7 billion times the mass of our Sun....
.
Observational history
Edwin HubbleEdwin Hubble
Edwin Powell Hubble was an American astronomer who profoundly changed the understanding of the universe by confirming the existence of galaxies other than the Milky Way - our own galaxy...
wrote the seminal paper N.G.C. 6822, A Remote Stellar System wherein he identified 15 variable stars (11 of which were Cepheids). He also surveyed the galaxy's stars distribution down to magnitude 19.4. He provided spectral characteristics, luminosities and dimensions for the five brightest "diffuse nebula" (giant H II region
H II region
An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...
s) that included the Bubble Nebula
Bubble Nebula (NGC 6822)
The Bubble Nebula in Barnard's Galaxy has the official designation of Hubble 1925 I as it was the first object recorded in . It includes areas of bright H II emission. It is located north-west of the larger Hubble III....
and the Ring Nebula
Ring Nebula (NGC 6822)
The Ring Nebula in Barnard's Galaxy has the official designation of Hubble 1925 III as it was the third object recorded in Hubble's 1925 paper, N.G.C. 6822, A Remote Stellar System. It includes areas of bright H II emission. In Paul W...
. He also computed the absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...
of the entire galaxy.
Hubble's detection of eleven Cepheid variable stars was a milestone in astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
. Utilizing the Cepheid Period-Luminosity relationship, Hubble determined a distance of more than 700,000 light-years. This was the first system beyond the Magellanic Clouds to have its distance accurately determined. (Hubble continued this process with the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
and the Triangulum Galaxy
Triangulum Galaxy
The Triangulum Galaxy is a spiral galaxy approximately 3 million light years from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598, and is sometimes informally referred to as the Pinwheel Galaxy, a nickname it shares with Messier 101...
). His distance to the galaxy was way beyond Harlow Shapley
Harlow Shapley
Harlow Shapley was an American astronomer.-Career:He was born on a farm in Nashville, Missouri, and dropped out of school with only the equivalent of a fifth-grade education...
's value of 300,000 light-years for the size of universe. In this paper, Hubble concluded "the Great Debate
The Great Debate
In astronomy, the Great Debate, also called the Shapley–Curtis Debate, was an influential debate between the astronomers Harlow Shapley and Heber Curtis which concerned the nature of spiral nebulae and the size of the universe...
" of 1920 between Heber Curtis
Heber Doust Curtis
Heber Doust Curtis was an American astronomer.He studied at the University of Michigan and at the University of Virginia, where he got a degree in astronomy....
and Shapley over the scale of the universe and the nature of the "spiral nebula". It soon became evident that all spiral nebulae were in fact spiral galaxies
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...
far outside our own Milky Way.
In 1977, Paul W. Hodge
Paul W. Hodge
Paul W. Hodge is an American astronomer.He was born in Washington. He earned an undergraduate degree in Physics from Yale and a doctorate in Astronomy from Harvard. In 1965 he and George Wallerstein created the astronomy department at the University of Washington, and he has been a professor...
extended the list of known H II regions in Barnard to 16. Today, there are over 150 of these regions cataloged in Barnard's Galaxy.
See also
- Bubble Nebula (NGC 6822)Bubble Nebula (NGC 6822)The Bubble Nebula in Barnard's Galaxy has the official designation of Hubble 1925 I as it was the first object recorded in . It includes areas of bright H II emission. It is located north-west of the larger Hubble III....
- Ring Nebula (NGC 6822)Ring Nebula (NGC 6822)The Ring Nebula in Barnard's Galaxy has the official designation of Hubble 1925 III as it was the third object recorded in Hubble's 1925 paper, N.G.C. 6822, A Remote Stellar System. It includes areas of bright H II emission. In Paul W...
- Large Magellanic CloudLarge Magellanic CloudThe Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...
- another irregular galaxy within the Local Group - Small Magellanic CloudSmall Magellanic CloudThe Small Magellanic Cloud is a dwarf galaxy. It has a diameter of about 7,000 light-years and contains several hundred million stars. It has a total mass of approximately 7 billion times the mass of our Sun....
- another irregular galaxy within the Local Group
External links
- The Milky Way's Tiny but Tough Galactic Neighbour — ESOESOESO, as a three-letter abbreviation, may stand for:* European Southern Observatory* Ensemble Studios Online* English Symphony Orchestra* Edmonton Symphony Orchestra* Executive Stock Options...
Press Release - NGC 6822: Barnard's Galaxy