| MadSci Network: Astronomy |
The latitude and longitude system used on other planets and moons is basically the same as that used on Earth. The coordinates for the planets and moons are determined by establishing a meridian, which is an imaginary line that runs from the North Pole to the South Pole (1). North and south poles exist on all the planets, even Uranus, which is tipped on its side, and moons, and the latitudes are determined relative to them, i.e., 0 to +90 and 0 to -90. The longitudes are determined in a variety of ways, as determined by the 1994 IAU Convention (2). For example, Titan always has the same face towards Saturn, and so that face is 0 longitude. The gas giant planets have no solid surface, and so their coordinates are tied to their magnetic fields.
The coordinate system on the Sun (3) is probably determined in the same way as for the gas giants, since it, too, has no solid surface. Unfortunately, I wasn't able to find any published information, so I direct you to the "Notes and References" section in any Astronomical Almanac.
The celestial coordinates, those that are specific to each object in the sky, are a little more difficult to establish (and understand!) See (4), (5), and (6) for a description of that and links to other sites.
Try the links in the MadSci Library for more information on Astronomy.