Sag DEG

Sag DEG is a small loop-shaped satellite galaxy of the Milky Way. It is known by other names, such as the Sagittarius dwarf elliptical galaxy or the Sagittarius dwarf spheroidal galaxy.

Sag DEG [1]
Observation data (J2000 epoch)
Constellation	Sagittarius
Right ascension	18h 55m 19.5s [2]
Declination	−30° 32′ 43″ [2]
Redshift	140 ± ? km/s [2]
Distance	65 ± 7 kly (20 ± 2 kpc) [3][4]
Apparent magnitude (V)	4.5 [2]
Characteristics
Type	dSph(t) [2]
Apparent size (V)	450′.0 × 216′.0 [2]
Notable features	Heading for a collision with the Milky Way
Other designations
Sagittarius dwarf elliptical galaxy,[5] Sgr dSph,[2] Sagittarius dwarf spheroidal,[2] Sgr I Dwarf [2]
See also: Galaxy, List of galaxies

Messier 54, believed to be at the core of Sag DEG. Greyscale image from the HST's Advanced Camera for Surveys

It consists of four globular clusters. The main cluster having been discovered in 1994. Sag DEG is about 10,000 light-years in diameter, and is about 70,000 light-years from Earth.

It moves in a polar orbit (i.e. an orbit passing through the galactic plane) at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud). In its looping, spiralling path, it has passed through the plane of the Milky Way several times in the past.^[6]

Sag DEG should not be confused with the Sagittarius dwarf irregular galaxy, or the Sag DIG, a small galaxy 3.4 million light-years distant.