I did some calculations and the nearest that Mars could come to Earth (if the semi-major axes of their orbits lined up) is 54,571,299km. (Perigee

_{Mars}=Perihelion

_{Mars}-Aphelion

_{Earth}) The farthest that the Moon can get from the Earth currently is 405,696km (Apogee

_{Moon}). This means that Mars would be at its closest 134.5 times farther away than the Moon at its farthest (Perigee

_{Mars}/Apogee

_{Moon}). So, for Mars to appear the same size as the moon, its radius would need to be 134.5 times as great as the Moon's. (This is the same reason that the Moon and Sun are about the same size in the sky; the Sun is about 400 times as large as and 400 times farther away than the Moon). The Moon's equatorial radius is 1738.14km, so Mars would need to be 233,802km in radius. This is 36.66 times that of the Earth, and 3.27 times that of Jupiter, the largest planet in the Solar system. For an even more dramatic comparison, Mars would need to have about 1/3 the radius of

*the Sun*. Mars, barring some very dramatic change in the orbits of the planets or of the Moon, will

*never*appear as large as the Moon in the Earth's sky. Math, internet people; L2math.