List of Andromeda's satellite galaxies
The Andromeda Galaxy has satellite galaxies just like the Milky Way. Orbiting M31 are at least 13 dwarf galaxies: 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 only starting from the 1970s.
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, possibly tracing the large-scale distribution of dark matter.
Table of known satellites
Andromeda Galaxy's satellites are listed here by discovery. 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.| Name | Type | Distance from Sun | Right Ascension** | Declination** | Absolute Magnitude | Magnitude | Mass-to-light ratio | Year discovered | Notes |
| M32 | dE2 | 2.48 | +9.2 | 1749 | |||||
| M110 | dE6 | 2.69 | +9.4 | 1773 | |||||
| NGC 185 | dE5 | 2.01 | +11 | 1787 | |||||
| NGC 147 | dE5 | 2.2 | +12 | 1829 | |||||
| Andromeda I | dSph | 2.43 | -11.8 | +13.2 | 31 ± 6 | 1970 | |||
| Andromeda II | dSph | 2.13 | -12.6 | +13 | 13 ± 3 | 1970 | |||
| Andromeda III | dSph | 2.44 | -10.2 | +10.3 | 19 ± 12 | 1970 | |||
| Andromeda V | dSph | 2.52 | -9.6 | +15.4 | 78 ± 50 | 1998 | |||
| Pegasus Dwarf Spheroidal | dSph | 2.55 | -11.5 | +14.5 | 12 ± 5 | 1998 | |||
| Cassiopeia Dwarf | dSph | 2.49 | -13.3 | +12.9 | 7.1 ± 2.8 | 1998 | |||
| Andromeda VIII | dSph | 2.7 | ' | ' | +9.1 | 2003 | |||
| Andromeda IX | dSph | 2.5 | -8.3 | +16.2 | 2004 | ||||
| Andromeda X | dSph | 2.9 | -8.1 | +16.2 | 63 ± 40 | 2005 | |||
| Andromeda XI | dSph | ' | ' | -7.3 | 2006 | ||||
| Andromeda XII | dSph | ' | ' | -6.4 | 2006 | ||||
| Andromeda XIII | dSph | -6.9 | 2006 | ||||||
| Andromeda XIV | dSph | -8.3 | 102 ± 71 | 2007 | |||||
| Andromeda XV | dSph | ' | ' | -9.4 | 2007 | ||||
| Andromeda XVI | dSph | -9.2 | 2007 | ||||||
| Andromeda XVII | dSph | ' | ' | -8.5 | 2008 | ||||
| Andromeda XVIII | dSph/Sm | 2008 | |||||||
| Andromeda XIX | dSph | ' | ' | -9.3 | 2008 | ||||
| Andromeda XX | dSph | -6.3 | 2008 | ||||||
| Andromeda XXI | dSph | ' | ' | -9.9 | 2009 | ||||
| Andromeda XXII | dSph | ' | ' | -7.0 | 2009 | ||||
| Andromeda XXIII | dIrr | 2011 | |||||||
| Andromeda XXIV | ' | ' | 2011 | ||||||
| Andromeda XXV | ' | ' | 2011 | ||||||
| Andromeda XXVI | 2011 | ||||||||
| Andromeda XXVII | ' | ' | 2011 | ||||||
| Andromeda XXVIII | dSph | 2011 | |||||||
| Andromeda XXIX | dIrr | 2011 | |||||||
| Tidal Stream Northwest | ' | ' | 2009 | ||||||
| Tidal Stream Southwest | ' | ' | 2009 | ||||||
| Triangulum Galaxy* | SAcd | 2.59 | +6.27 | 1654? | Exact distance and relation to Andromeda uncertain |
* It is uncertain whether it is a companion galaxy of the Andromeda Galaxy.
** RA/DEC values marked in Italics are rough estimates.