Figure 11-2 RIVUXG Apparent Magnitude Scale (a) Several stars in and around the constellation Orion, labeled with their names and apparent magnitudes. For a discussion of star names, see Guided Discovery: Star Names. (b) Astronomers denote the brightnesses of objects in the sky by their apparent magnitudes. Stars visible to the naked eye have magnitudes between m = −1.44 (Sirius) and about m = +6.0. However, CCD (charge-coupled device) photography through the Hubble Space Telescope or a large Earth-based telescope can reveal stars and other objects nearly as faint as magnitude m = +30. Note that Pluto’s apparent magnitude varies from +13.7 to +16.3, depending on its distance from Earth. Its average apparent magnitude is +15.1.