The common distance measures we use depend on what we are measuring. For distances within our solar system, or other solar systems, the common unit is the 'Astronomical Unit' (A.U.)1 A.U. = the average distance between the Earth and the Sun. For most everything else, stars, galaxies etc..., the distance unit is the parsec (pc). This is a convenient unit when measuring distances to stars by triangulation (what astronomers call parallax).1 pc = 3.26 light years = about the distance to the nearest star.1 pc = 60 x 60 x 180/pi A.U. = 206265 A.U. --- by definition. for distances within our galaxy or other galaxies it is kiloparsecs (kpc):1 kpc = 1,000 for distances between galaxies, and cosmology it is Megaparsecs (Mpc).1 Mpc = 1,000,000 pc 3. The exception to these is when one is studying smaller object, such as a star or a planet. Then we might use kilometers. For dust grains, we might use microns (1/1,000,000 of a meter).4. It is also common to compare objects. For example, if one is studying a star one might say "its radius is 5 solar radii", meaning it is 5 times the size of our sun. Similarly with galaxies, is it bigger or smaller than the Milky Way.

Mars is 14901 hours far from the earth. He typical time during Mars's closest approach to the Earth every 1.6 years is about 260 days. Humans can get to mars because the have the tools to get there.