Extraterrestrial skies Mars appears to be the angular diameter as seen from Earth (0.35°), and sends 40% of the light, approximately the brightness of a slightly cloudy afternoon on Earth. On June 3, 2014, the "Curiosity" rover on Mars observed the planet Mercury transiting the Sun, marking the first time a planetary transit has been observed from a celestial body besides Earth. Mars has two small moons: Phobos and Deimos. From the Martian surface, Phobos has one-third to one-half the angular diameter of the Sun while Deimos is barely more than a dot (only 2′ angular diameter). The orbital period of Phobos
Phobos (moon) presence of voids and indicate that it is not a solid chunk of rock but a porous body. The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third being empty. Phobos has been photographed in close-up by several spacecraft whose primary mission has been to photograph Mars. The first was "Mariner 7" in 1969, followed by "Viking 1" in 1977, "Mars Global Surveyor" in 1998 and 2003, "Mars Express" in 2004, 2008, and 2010, and "Mars Reconnaissance Orbiter" in 2007 and 2008. On August 25, 2005, the "Spirit" rover, with an excess of