Illustration Comparing Apparent Sizes of Moons
Date: 15 Aug 2013
This illustration provides a comparison for how big the moons of Mars appear to be, as seen from the surface of Mars, in relation to the size that Earth's moon appears to be when seen from the surface of Earth. Earth's moon actually has a diameter more than 100 times greater than the larger Martian moon, Phobos. However, the Martian moons orbit much closer to their planet than the distance between Earth and Earth's moon.
Deimos, at far left, and Phobos, beside it, are shown together as they actually were photographed by the Mast Camera (Mastcam) NASA's Mars rover Curiosity on 1 Aug. 2013. The images are oriented so that north is up. The size-comparison image of Earth's moon, on the right, is also oriented with north up.
Deimos has a diameter of 12 km (7.5 miles) and was 20,500 km (12,800 miles) from the rover at the time of the image. Phobos has a diameter 22 km (14 miles) and was 6,240 km (3,900 miles) from the rover at the time of the image. Earth's moon has a diameter of 3,474 km (2,159 miles) and is typically about 380,000 km (238,000 miles) from an observer on Earth.
Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.