# Astronomy/Mars and Jupiter

Question
Could a human being with perfect eyesight see Jupiter in the Martian night-sky, without using a telescope? If so, how big would Jupiter seem compared to the size of the Full Moon in our own night-sky? I was thinking that we can sort of see Venus at night unaided, and that therefore Jupiter, being many times bigger than Venus and a lot closer to Mars than to Earth, would be relatively visible as a small globe in the night-sky.

Hi Geoff,

I've used the closest approach of Venus to Earth (37.8 million km), and the closest Mars gets to Jupiter (555 million km). Then, from the size of the two planets, you can calculate their angular size in the sky. You can check my math by going to http://en.wikipedia.org/wiki/Angular_diameter

Using those values, the maximum size Venus gets (seen from earth) is about 63" of arc. You're correct - good eyes can barely make out a disk. The maximum size Jupiter gets (seen from Mars) is 51" of arc (slightly smaller in the sky). So even though Jupiter is much larger than Venus, it is still much, much farther away, and actually appears smaller than Venus.

Prof. James Gort

Astronomy

Volunteer

#### James Gort

##### Expertise

Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.

##### Experience

I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

Publications
StarDate, University of Texas, numerous Journal Publications