The most common type of galaxy in the Universe, although not recognized until 1938 (the Sculptor dwarf was the first example discovered) because of their low luminosity and low surface brightness; symbol dSph. Dwarf spheroidals are similar to ellipticals in that they contain little or no interstellar material, but they are not so centrally concentrated and have low density, low surface brightness, and a decrease of light output with radius which implies that they are more closely related to small disk galaxies. Dwarf spheroidals have diameters up to about 10 000 l.y. and masses up to about 10⁷ Suns. Half the galaxies of the Local Group are dwarf spheroidals, mostly clustered around M31 and our own Galaxy.