C17

C17 and C18 are a pair of small spheroidal galaxies in the southern regions of Cassiopeia, near its border with Andromeda. They are in fact part of the Andromeda Galaxy's extensive system of satellites and associated galaxies (the main Andromeda Galaxy itself lies slightly to the south from C17 and C18). Both of these satellite galaxies are relatively small by galactic standards, with C17 being marginally smaller than its neighbour at about 7,000 light years in diameter.

Of the two dwarf galaxies, C17 appears to be some 2,500,000 light years from the Milky Way, making it more distant than C18 by approximately 400,000 light years (though still a very near neighbour of the Milky Way, in cosmic terms). There is no evidence of star formation within the galaxy for several million years, and for this reason it is composed primarily of older and redder stars.