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hbcondo714

> You would see two moons in that sky instead of one

Any pictures of this?

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There are some videos (from pictures) of eclipses, which show both: https://www.youtube.com/watch?v=M_Kn3M2ierk

This one more zoomed out, but only with Phobos: https://www.youtube.com/watch?v=ViiriVhIhjE

Taking into account that the Sun itself is seen smaller than on Earth, we can already imagine the view. The main problem would be that "Phobos is one of the least reflective bodies in the Solar System, with an albedo of just 0.071.".

This makes me appreciate our moon.

How lucky we are to have a moon that is roughly the same size in the sky as the sun is -- aligned such that we occasionally get to see a perfect solar eclipse and the sun's corona with our naked eyes.

> aligned such that we occasionally get to see a perfect solar eclipse and the sun's corona with our naked eyes.

Uh...don't do that. It'll end up being the last thing you see.

A total eclipse is perfectly safe to view with the naked eye. You just have to be carful you don't start too early or end too late...

Many references, but e.g., https://eclipse2017.nasa.gov/safety "Looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”)..."

In fact I viewed the 1976 total eclipse in Oregon with binoculars.

It was a glorious sight, an experience of a lifetime.

I was on a hillside near The Dalles with other eclipse chasers. Many of us wore sunglasses and looked away from the sun before totality to get our eyes a bit dark-adapted. And then when someone called out "totality!" we turned around, took off the sunglasses and used our binoculars or telescopes if we had them, and viewed the corona directly.

And no, no eye damage.

I don't want to suggest this is a _good_ idea, but I spent a lot of time staring directly at the sun as a kid without any apparent damage to my eyes.

It's safe.

Also, it's more spherical than the moons of Mars.

Anything as big as the Moon is going to be spherical; if Mars' moons were large enough to totally eclipse the Sun, I expect they would be spherical too.

If you get far enough away from the sun you could potentially see a total eclipse with a lumpy moon. Or if the moon has a very low orbit. For Mars, Phobos is probably about as close to an eclipse-with-a-lumpy-moon as you could reasonably expect to get. I think it's not that far above the Roche limit where it would fall apart and turn into a ring, and if it were bigger it would tend to be less lumpy. Potentially you could stretch it into a pancake-shape which would better occlude the sun by spinning it, but I suppose that would also make it more likely to fall apart and turn into a ring.

Mars’ moons are more like asteroids though

0.07 doesn't sound like a show stopper. The moon is 0.12, so Phobos reflects 40% less light for that reason. The sun being further away (1.5 AU) has a bigger effect due to the inverse square law - that costs 55% of the light. But the biggest effect would come from the fact that it's tiny, about 0.65% of the radius of the moon, orbiting 60x closer, which two factors combine to make it another 60% dimmer than the moon. Then there's the atmosphere which I expect to have a relatively small effect assuming good conditions on both Earth and Mars.

So overall I estimate it should be 0.6 x 0.45 x 0.4 = 0.1, or about one-tenth as bright as the moon, or apparent magnitude -10. That would make it far brighter than we see Venus or Jupiter, but makes me question the assertion in TFA that it would cast shadows - I don't expect many shadows on earth when the moon is one day old.

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