Albedo distribution of solar radiation reaching the Earth's surface. These factors vary with atmospheric composition, geographic location and time (see position of the Sun). While bi-hemispherical reflectance is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages. Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is often given
Albedo feature regio. On bodies with a very thick atmosphere like Venus or Titan, permanent albedo features cannot be seen using ordinary optical telescopes because the surface is not visible, and only clouds and other transient atmospheric phenomena are seen. The "Cassini–Huygens" probe observed multiple albedo features on Titan after its arrival in Saturn's orbit in 2004. The very first albedo feature ever seen on another planet was Syrtis Major Planum on Mars in the 17th century. Today, thanks to space probes, very high-resolution images of surface features on Mars and Mercury are available, and the classical nomenclature based on albedo features