an atmosphere that is relatively transparent at optical wavelengths (just like Earth, albeit much thinner), meteors will occasionally be seen. Meteor showers Many astronomical phenomena viewed from the planet Mars are the same as or similar to those seen from Earth; but some (e.g. the view of Earth as an evening/morning star) are quite different. For example, because the atmosphere of Mars does not contain an ozone layer, it is also possible to make UV observations from the surface of Mars. The first meteor photographed on Mars (on March 7, 2004, by the Spirit rover) is now believed to have been part of a meteor shower whose parent body was comet 114P/Wiseman-Skiff. Because the radiant was in the constellation Cepheus, this meteor shower could be dubbed the Martian Cepheids. As on Earth, when a meteor is large enough to actually impact with the surface (without burning up completely in the atmosphere), it becomes a meteorite. The first known meteorite discovered on Mars (and the third known meteorite found someplace other than Earth) was Heat Shield Rock. The first and the second ones were found on the Moon by the Apollo missions. On October 19, 2014, Comet Siding Spring passed extremely close to Mars, so close that the coma may have enveloped the planet. Many astronomical phenomena viewed from the planet Mars are the same as or similar to those seen from As seen from Mars, the Earth is an inner planet like Venus (a "morning star" or "evening star"). The Earth and Moon appear starlike to the naked eye, but observers with telescopes would see them as crescents, with some detail visible. The moon Phobos appears about one third the angular diameter that the full Moon appears from Earth; on the other hand, Deimos appears more or less starlike with a disk barely discernible if at all. Phobos orbits so fast (with a period of just under one third of a sol) that it rises in the west and sets in the east, and does so twice per sol; Deimos on the other hand rises in the east and sets in the west, but orbits only a few hours slower than a Martian sol, so it spends about two and a half sols above the horizon at a time. The maximum brightness of Phobos at "full moon" is about magnitude −9 or −10, while for Deimos it is about −5. By comparison, the full Moon as seen from Earth is considerably brighter at magnitude −12.7. Phobos is still bright enough to cast shadows; Deimos is only slightly brighter than Venus is from Earth. Just like Earth's Moon, both Phobos and Deimos are considerably fainter at non-full phases. Unlike Earth's Moon, Phobos's phases and angular diameter visibly change from hour to hour; Deimos is too small for its phases to be visible with the naked eye. Both Phobos and Deimos have low-inclination equatorial orbits and orbit fairly close to Mars. As a result, Phobos is not visible from latitudes north of 70.4°N or south of 70.4°S; Deimos is not visible from latitudes north of 82.7°N or south of 82.7°S. Observers at high latitudes (less than 70.4°) would see a noticeably smaller angular diameter for Phobos because they are farther away from it. Similarly, equatorial observers of Phobos would see a noticeably smaller angular diameter for Phobos when it is rising and setting, compared to when it is overhead. Since Mars has an atmosphere that is relatively transparent at optical wavelengths (just like Earth, albeit much thinner), meteors will occasionally be seen. Meteor showers on Earth occur when the Earth intersects the orbit of a comet, and likewise, Mars also has meteor showers, although these are different from the ones on Earth. The first meteor photographed on Mars (on March 7, 2004, by the Spirit rover) is now believed to have been part of a meteor shower whose parent body was comet 114P/Wiseman-Skiff. Because the radiant was in the constellation Cepheus, this meteor shower could be dubbed the Martian Cepheids. As on Earth, when a meteor is large enough to actually impact with the surface (without burning up completely in the atmosphere), it becomes a meteorite. The first known meteorite discovered on Mars (and the third known meteorite found someplace other than Earth) was Heat Shield Rock. The first and the second ones were found on the Moon by the Apollo missions. On October 19, 2014, Comet Siding Spring passed extremely close to Mars, so close that the coma may have enveloped the planet. As on Earth, the effect of precession causes the north and south celestial poles to move in a very large circle, but on Mars the cycle is 95,500 Martian years (179,600 Earth years) rather than 26,000 years as on Earth. As on Earth, there is a second form of precession: the point of perihelion in Mars's orbit changes slowly, causing the anomalistic year to differ from the sidereal year. However, on Mars, this cycle is 43,000 Martian years (81,000 Earth years) rather than 112,000 years as on Earth. On both Earth and Mars, these two precessions are in opposite directions, and therefore add, to make the precession cycle between the tropical and anomalistic years 21,000 years on Earth and 29,700 Martian years (55,900 Earth years) on Mars. As on Earth, the period of rotation of Mars (the length of its day) is slowing down. However, this effect is three orders of magnitude smaller than on Earth because the gravitational effect of Phobos is negligible and the effect is mainly due to the Sun. On Earth, the gravitational influence of the Moon has a much greater effect. Eventually, in the far future, the length of a day on Earth will equal and then exceed the length of a day on Mars. As on Earth, Mars experiences Milankovitch cycles that cause its axial tilt (obliquity) and orbital eccentricity to vary over long periods of time, which has long-term effects on its climate. The variation of Mars's axial tilt is much larger than for Earth because it lacks the stabilizing influence of a large moon like Earth's Moon. Mars has a 124,000-year obliquity cycle compared to 41,000 years for Earth.