Albedo planet would drop to about 0 °C. In contrast, if the entire Earth was covered by water — a so-called aquaplanet — the average temperature on the planet would rise to almost 27 °C. For land surfaces, it has been shown that the albedo at a particular solar zenith angle "θ" can be approximated by the proportionate sum of two terms: the directional-hemispherical reflectance at that solar zenith angle, formula_1, and the bi-hemispherical reflectance, formula_2, with formula_3 being the proportion of direct radiation from a given solar angle, and formula_4 being the proportion of diffuse illumination. Hence, the actual albedo
Albedo feature Albedo feature An albedo feature is a large area on the surface of a planet (or other solar system body) which shows a contrast in brightness or darkness (albedo) with adjacent areas. Historically, albedo features were the very first (and usually only) features to be seen and named on Mars and Mercury. Early classical maps (such as those of Schiaparelli and Antoniadi) showed only albedo features, and it was not until the arrival of space probes that other surface features such as craters could be seen. On bodies other than Mars and Mercury, an albedo feature is sometimes called a