Introduction

Dwarf spheroidals are the most common type of galaxy in the Universe. The fact that they were not discovered until 1938 is entirely due to their feeble luminosity and low surface brightness. Of the 29 galaxies that are known to be located within 1.0 Mpc, approximately half are dwarf spheroidals (dSph). A listing of these Local Group dSph galaxies is given in Table 14. For the sake of completeness the dSph/dE galaxies NGC 147 and NGC 185, which are both brighter than Mv= −15.0, have been included in the table. Since most of the faintest known Local Group members are dwarf spheroidals it is almost certain that additional very faint dSph galaxies remain to be discovered in the Local Group. In particular it seems probable that more dSph companions to M31 will eventually be found. Only three such objects (And I, And II and And III) are presently known (van den Bergh 1972), whereas seven dSph companions (Sgr, UMi, Dra, Scl, Sex, Car, For) are known to be located within 150 kpc of the Galaxy – even though the Milky Way system is less luminous than the Andromeda nebula. It is, of course, possible that the small number of M31 dSph satellites is due to the fact that some dwarf companions to M31 were destroyed by tidal interactions with M32 and NGC 205. For reviews on dwarf spheroidal galaxies the reader is referred to Da Costa (1992), Gallagher & Wyse (1994) and Ferguson & Binggeli (1994).