Geometric albedo node of their orbit, and hence lie on the ecliptic. In practice, measurements at small nonzero phase angles are used to derive the parameters which characterize the directional reflectance properties for the body (Hapke parameters). The reflectance function described by these can then be extrapolated to zero phase angle to obtain an estimate of the geometric albedo. For very bright, solid, airless objects such as Saturn's moons Enceladus and Tethys, whose total reflectance (Bond albedo) is close to one, a strong opposition effect combines with the high Bond albedo to give them a geometric albedo above unity (1.4 in the
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