observers on the surface of Mars can't see. The phenomenon of libration occurs for Phobos as it does for Earth's Moon, despite the low inclination and eccentricity of Phobos's orbit. Due to the effect of librations and the parallax due to the close distance of Phobos, by observing at high and low latitudes and observing as Phobos is rising and setting, the overall total coverage of Phobos's surface that is visible at one time or another from one location or another on Mars's surface is considerably higher than 50%. The large Stickney crater is visible along one edge of the face of Phobos. It would be easily visible with the naked eye from the surface of Mars. Comets and meteors 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. Auroras Auroras occur on Mars, but they do not occur at the poles as on Earth, because Mars has no planetwide magnetic field. Rather, they occur near magnetic anomalies in Mars's crust, which are remnants from earlier days when Mars did have a magnetic field. Martian auroras are a distinct kind not seen elsewhere in the Solar System. They would probably also be invisible to the human eye, being largely ultraviolet phenomena. Celestial poles and ecliptic The orientation of Mars's axis is such that its north celestial pole is in Cygnus at R.A. Decl. (or