A Conversation for SEx - Science Explained

SEx: Phases of the Martian Moons

Post 1

Apollyon - Grammar Fascist

If I lived on Mars, would I be able to make out phases in Phobos and Deimos with a naked eye (or at least one shielded by nothing more than my space suit's helmet)?


SEx: Phases of the Martian Moons

Post 2

Gnomon - time to move on

Mars has two moons.

Phobos is about 12 km in diameter, and orbits Mars at a distance of 9380 km. This means that it should be only about one seventh that apparent diameter of our moon in the sky. That's still big enough to make out phases.

Phobos's most distinctive feature is its speed - it does a full orbit in under 8 hours.

The moon will rise as a crescent, wax to full, wane back to a crescent and set, all in less than 4 hours.

Deimos is slower and more sedate. It will do something similar, but more slowly. It also will look smaller in size than Phobos.


SEx: Phases of the Martian Moons

Post 3

Gnomon - time to move on

Of course, being so close to the planet, Phobos would probably be eclipsed regularly, and would not be a full moon, but an eclipsed one.


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