Albedo formula_5 (also called blue-sky albedo) can then be given as: Directional-hemispherical reflectance is sometimes referred to as black-sky albedo and bi-hemispherical reflectance as white-sky albedo. These terms are important because they allow the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface. The albedos of planets, satellites and minor planets such as asteroids can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time comprises a major part of the astronomical field of photometry. For small
Classical albedo features on Mars topographic features on Mars are still based on the classical nomenclature for the feature's location; for instance, the albedo feature 'Ascraeus Lacus' provides the basis of the name of the volcano "Ascraeus Mons" in roughly the same position. In addition, since most Earth-based amateur telescopes are not powerful enough to resolve the topographic surface features of Mars, amateur astronomers still use many of the old feature-names to orient themselves and record their observations. Several Latin words involved here are common nouns. These are generally, but not always, second in the name, but are usually ignored in alphabetizing below: Not listed