Albedo used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly, which is a common source of confusion. In detailed studies, the directional reflectance properties of astronomical bodies are often expressed in terms of the five Hapke parameters which semi-empirically describe the variation of albedo with phase angle, including a characterization of the opposition effect of regolith surfaces. The correlation between astronomical (geometric) albedo, absolute magnitude and diameter is: formula_7, where formula_8 is the astronomical albedo, formula_9
Martian surface little light at the blue end of the spectrum but much at red and higher wavelengths. This is why Mars has the familiar reddish-orange color to the naked eye. But detailed observations reveal a subtle range of colors on Mars' surface. Color variations provide clues to the composition of surface materials. The bright areas are reddish-ochre in color, and the dark areas appear dark gray. A third type of area, intermediate in color and albedo, is also present and thought to represent regions containing a mixture of the material from the bright and dark areas. The dark gray areas can