NGC 185
Encyclopedia
NGC 185 is a dwarf spheroidal galaxy
about 2.08 million
light-year
s away in the constellation
Cassiopeia
. It is a member of the Local group
, and is a satellite galaxy
of the Andromeda Galaxy
(M31). NGC 185 was discovered by William Herschel
on November 30, 1787, and he cataloged it "H II.707". John Herschel
observed the object again in 1833 when he cataloged it as "h 35", and then in 1890 when he cataloged it as "GC 90" within his General Catalogue of Nebulae and Clusters. NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory
. Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus
(AGN) and is classified as a type 2 Seyfert galaxy
.
(640 ± 50 kpc
). However, NGC 185 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to NGC 185 using this technique is 2.02 ± 0.2 Mly (620 ± 60 kpc). Averaged together, these distance measurements give a distance estimate of 2.05 ± 0.13 Mly (630 ± 40 kpc).average (640 ± 50, 620 ± 60) = ((640 + 620) / 2) ± ((502 + 602)0.5 / 2) = 630 ± 40
history of NGC 185 and found that the majority of star formation in NGC 185 happened at early times. In the last ~1 Gyr, stars have formed only near the center of this galaxy. Walter Baade
discovered young blue objects within this galaxy in 1951, but these have turned out to be star clusters and not individual stars. A supernova remnant
near the center was also discovered by Martínez-Delgado et al.
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
about 2.08 million
1 E19 m
To help compare different orders of magnitude, this page lists distances starting at 10 Em .Distances shorter than 10 Em* 13 Em — 1,300 light years — Distance to the Orion Nebula...
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....
Cassiopeia
Cassiopeia (constellation)
Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopea was one of the 48 constellations listed by the 2nd century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. It is a member 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...
, and is a satellite galaxy
Satellite galaxy
A satellite galaxy orbits a larger galaxy due to gravitational attraction. Although a galaxy is made of a large number of objects which are not connected to each other, it has a center of mass, which represents a weighted average of the positions of each component object...
of 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...
(M31). NGC 185 was discovered by William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
on November 30, 1787, and he cataloged it "H II.707". John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
observed the object again in 1833 when he cataloged it as "h 35", and then in 1890 when he cataloged it as "GC 90" within his General Catalogue of Nebulae and Clusters. NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory
Lick Observatory
The Lick Observatory is an astronomical observatory, owned and operated by the University of California. It is situated on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, USA...
. Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
(AGN) and is classified as a type 2 Seyfert galaxy
Seyfert galaxy
Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943...
.
Distance measurements
At least two techniques have been used to measure distances to NGC 185. The surface brightness fluctuations distance measurement technique estimates distances to galaxies based on the graininess of their appearance. The distance measured to NGC 185 using this technique is 2.08 ± 0.15 MlyLight-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
(640 ± 50 kpc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
). However, NGC 185 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to NGC 185 using this technique is 2.02 ± 0.2 Mly (620 ± 60 kpc). Averaged together, these distance measurements give a distance estimate of 2.05 ± 0.13 Mly (630 ± 40 kpc).average (640 ± 50, 620 ± 60) = ((640 + 620) / 2) ± ((502 + 602)0.5 / 2) = 630 ± 40
Star formation
Martínez-Delgado, Aparicio, & Gallart (1999) looked into the star formationStar formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
history of NGC 185 and found that the majority of star formation in NGC 185 happened at early times. In the last ~1 Gyr, stars have formed only near the center of this galaxy. Walter Baade
Walter Baade
Wilhelm Heinrich Walter Baade was a German astronomer who worked in the USA from 1931 to 1959.-Biography:He took advantage of wartime blackout conditions during World War II, which reduced light pollution at Mount Wilson Observatory, to resolve stars in the center of the Andromeda galaxy for the...
discovered young blue objects within this galaxy in 1951, but these have turned out to be star clusters and not individual stars. A supernova remnant
Supernova remnant
A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
near the center was also discovered by Martínez-Delgado et al.