4 ms·

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

by Medox 6y ago

There are some videos (from pictures) of eclipses, which show both: https://www.youtube.com/watch?v=M_Kn3M2ierk https://www.youtube.com/watch?v=M_Kn3M2ierk This one more zoomed out, but only with Phobos: https://www.youtube.com/watch?v=ViiriVhIhjE 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.".

nostromo 6y ago
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.
- amelius 6y ago
  Also, it's more spherical than the moons of Mars.
  - edgyquant 6y ago
    Mars’ moons are more like asteroids though
  - azernik 6y ago
    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.
    - elihu 6y ago
      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.
- giantrobot 6y ago
  > 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.
  - eclarkso 6y ago
    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 https://eclipse2017.nasa.gov/safety "Looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”)..."
    - Stratoscope 6y ago
      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.
  - peteretep 6y ago
    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.
  - gsich 6y ago
    It's safe.
dmurray 6y ago
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.

by Medox 6y ago

nostromo 6y ago

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.

amelius 6y ago
Also, it's more spherical than the moons of Mars.
- edgyquant 6y ago
  Mars’ moons are more like asteroids though
- azernik 6y ago
  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.
  - elihu 6y ago
    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.
giantrobot 6y ago
> 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.
- eclarkso 6y ago
  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 https://eclipse2017.nasa.gov/safety "Looking directly at the sun is unsafe except during the brief total phase of a solar eclipse (“totality”)..."
  - Stratoscope 6y ago
    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.
- peteretep 6y ago
  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.
- gsich 6y ago
  It's safe.

dmurray 6y ago

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.