List of Andromeda's satellite galaxies

The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 35 dwarf galaxies:^[1] the brightest and largest is M110, which can be seen with a basic telescope. The second-brightest and closest one to M31 is M32. The other galaxies are fainter, and were mostly discovered starting from the 1970s.

The Andromeda Galaxy with M110 at upper left and M32 to the right of the core

On January 11, 2006, it was announced that Andromeda Galaxy's faint companion galaxies lie on or close to a single plane running through the Andromeda Galaxy's center. This unexpected distribution is not obviously understood in the context of current models for galaxy formation. The plane of satellite galaxies points toward a nearby group of galaxies (M81 Group), possibly tracing the large-scale distribution of dark matter.

It is unknown whether the Triangulum Galaxy is a satellite of Andromeda.

Table of known satellites

Andromeda Galaxy's satellites are listed here by discovery (orbital distance is not known). Andromeda IV is not included in the list, as it was discovered to be roughly 10 times further than Andromeda from the Milky Way in 2014, and therefore a completely unrelated galaxy.

Andromeda Galaxy's satellites

Name	Type	Distance from Sun (million ly)	Right Ascension**	Declination**	Absolute Magnitude[2]	Apparent magnitude	Mass-to-light ratio	3D distance to M31 (kly)	Year discovered	Notes
M32	dE2	2.48	00h 42m 41.877s	+40° 51′ 54.71″		+8.1			1749
M110	dE6	2.69	00h 40m 22.054s	+41° 41′ 08.04″	−16.5	+8.5			1773
NGC 185	dE5	2.01	00h 38m 57.523s	+48° 20′ 14.86″		+10.1			1787
NGC 147	dE5	2.2	00h 33m 12.131s	+48° 30′ 32.82″		+10.5			1829
Andromeda I	dSph	2.43	00h 45m 39.264s	+38° 02′ 35.17″	−11.8	+13.6	31 ± 6[2]		1970
Andromeda II***	dSph	2.13	01h 16m 28.136s	+33° 25′ 50.36″	−12.6	+13.5	13 ± 3[2]		1970
Andromeda III	dSph	2.44	00h 35m 31.777s	+36° 30′ 04.19″	−10.2	+15.0	19 ± 12[2]		1970
Andromeda V	dSph	2.52	01h 10m 16.952s	+47° 37′ 40.12″	−9.6	+15.9	78 ± 50[3]		1998
Pegasus Dwarf Spheroidal (Andromeda VI)	dSph	2.55	23h 51m 46.516s	+24° 34′ 55.69″	−11.5	+14.2	12 ± 5[3]		1998
Cassiopeia Dwarf (Andromeda VII)	dSph	2.49	23h 26m 33.321s	+50° 40′ 49.98″	−13.3	+12.9	7.1 ± 2.8[2]		1998
Andromeda VIII	dSph	2.7	00h 42m 06s	+40° 37′ 00″		+9.1			2003	Tidally disrupting; identification unclear
Andromeda IX	dSph	2.5	00h 52m 52.493s	+43° 11′ 55.66″	−8.3	+16.2		127.2	2004
Andromeda X	dSph	2.9	01h 06m 34.740s	+44° 48′ 23.31″	−8.1	+16.1	63 ± 40[2]	332.7	2005
Andromeda XI[4]	dSph		00h 46m 20s	+33° 48′ 05″	−7.3				2006
Andromeda XII[4]	dSph		00h 47m 27s	+33° 22′ 29″	−6.4				2006
Andromeda XIII[4] (Pisces III)	dSph		00h 51m 49.555s	+33° 00′ 31.40″	−6.9				2006
Andromeda XIV[5] (Pisces IV)	dSph		00h 41m 35.219s	+29° 41′ 45.87″	−8.3		102 ± 71[2]		2007
Andromeda XV[5]	dSph		01h 14m 18.7s	+38° 07′ 02.9″	−9.4				2007
Andromeda XVI[5] (Pisces V)	dSph	2.143[6]	00h 59m 29.843s	+32° 22′ 27.96″	−9.2			580.6	2007
Andromeda XVII[5]	dSph		00h 37m 07s	+44° 19′ 20″	−8.5			313.1	2008
Andromeda XVIII[5]	dSph/Sm		00h 02m 15.184s	+45° 05′ 19.78″				515.3	2008
Andromeda XIX[5]	dSph		00h 19m 32.1s	+35° 02′ 37.1″	−9.3				2008
Andromeda XX[5]	dSph		00h 07m 30.530s	+35° 07′ 45.94″	−6.3			512.1	2008
Andromeda XXI[5]	dSph		23h 54m 47.7s	+42° 28′ 15″	−9.9			472.9	2009
Andromeda XXII[5]	dSph		00h 27m 40s	+28° 05′ 25″	−7.0			910	2009
Andromeda XXIII[5]	dIrr		01h 29m 21.944s	+38° 43′ 05.97″				427.3	2011
Andromeda XXIV[5]			01h 18m 30s	+46° 21′ 58″				401.2	2011
Andromeda XXV[5]			00h 30m 08.9s	+46° 51′ 07″				319.6	2011
Andromeda XXVI[5]			00h 23m 45.6s	+47° 54′ 58″				489.2	2011
Andromeda XXVII[5]			00h 37m 27.1s	+45° 23′ 13″					2011	Tidally disrupted[7]
Andromeda XXVIII[8]	dSph		22h 32m 41.449s	+31° 12′ 59.10″	−8.8[9]				2011
Andromeda XXIX[8]	dIrr		23h 58m 55.440s	+30° 45′ 22.09″				636	2011
Andromeda XXX (Cassiopeia II)[10]	dSph?		00h 36m 34.9s	+49° 38′ 48″
Andromeda XXXI (Lacerta I)[10]	dSph?		22h 58m 16.3s	+41° 17′ 28″					2013
Andromeda XXXII (Cassiopeia III)[10]	dSph?	2.74[11]	00h 35m 59.4s	+51° 33′ 35″				508[11]	2013
Andromeda XXXIII (Perseus I)[10]	dSph?	2.41[11]	03h 01m 23.6s	+40° 59′ 18″				1,140[11]	2013
Tidal Stream Northwest (Tidal Stream E and F)[12]			00h 20m 00s	+46° 00′ 00″					2009
Tidal Stream Southwest[12]			00h 30m 00s	+37° 30′ 00″					2009
Pegasus V galaxy (Peg V, Andromeda XXXIV)	d	682 kpc (2.22 Mly)	23h 18m 27.8s±0.1	+33° 21′ 32″±3	−6.3			800	2022	[13][14][15]
Andromeda XXXV[16]		3.02	00h 26m 38.6s	+40° 06′ 29.3″	-5.2			520	2025
Triangulum Galaxy* (M33)	SA(s)cd	2.59	01h 33m 50.883s	+30° 39′ 36.54″		+6.27		750[17]	1654?	Its relation to Andromeda is uncertain.

^* It is uncertain whether it is a companion galaxy of the Andromeda Galaxy.

^** RA/DEC values marked in Italics are rough estimates.

^*** Martin et al. (2009) gave aliases to several satellite galaxies of the Andromeda Galaxy that are located in Pisces.^[18] However, the name Pisces II was later used for a different galaxy that is a satellite of the Milky Way,^[19] so it is not used here.

See also

• Satellite galaxies of the Milky Way
• List of nearest galaxies
• Local Group