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1500 questions
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How do we distinguish old craters from new ones on the Moon?
The following image is the observation made by the Dual Frequency Synthetic Aperture Radar (DF-SAR) onboard the Chandrayaan-2 Orbiter:
Due to image size restriction, a lower resolution image is used here. In case you wish to see the original image,…
Vishnu
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9th planet location?
I've seen a number of news reports indicating there is likely a 9th planet in our Solar System, something with an orbital period of between 10k-20k years, that is 10 times Earth's mass. I haven't seen any real indication of where this object might…
PearsonArtPhoto
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Is the influence of gravity instantaneous?
When I was in college, I posed to my astronomy professor a thought experiment that had been puzzling my mind for some time: "If all the matter in the Sun magically disappeared instantly, how long would it take its gravity to stop having an effect on…
Ky -
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Is it a coincidence that on the far side of the moon almost no seas are visible?
Sorry for the maybe too large pictures. They do make the surface structures of both sides of the moon visible though. Is it just a coincidence that on the side facing us is so much sea is visible?
It looks as if on the far side more meteorites have…
Deschele Schilder
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Is Venus in some way tidally locked to... Earth?
The video here demonstrates how Earth sees the same face of Venus every inferior conjunction (i.e., two planets are the closest to each other):
https://www.youtube.com/watch?v=4m_ouMC61-w (or…
puzzlet
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If you lived on the far side of the Moon, how could you infer the existence of Earth?
Suppose that you deposit an astronomer, armed with our current knowledge of orbital mechanics, on a dome on the far side of the Moon, so that the Earth is perpetually hidden from them.
(And, of course, assume that this person has no specific…
Emilio Pisanty
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39
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4 answers
Why does the Moon appear gray when passing between the Sun and the Earth?
Shouldn't the Moon appear as bright as a full Moon seen at midnight from Earth?
The photo was taken by DSCOVR at Lagrange point 1.
In the picture, The Moon appears dark gray. Of course the Earth appears bright, reflecting sunlight from clouds and…
Brian Leeming
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2 answers
Why are the Pillars of Creation pillar-shaped?
The Pillars of Creation have a strong directional sense. They are referred to as "pillars" and another question asks how "tall" they are. Naively, it looks as if there is a source of "smoke" near the tips of the pillars, and the smoke is being blown…
Mark Foskey
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How can comets have tails if there's no air resistance in space?
I understand that solar radiation causes material to vaporize out of a comet into dust but why does the dust then trail behind the comet like a "tail"?
Assuming gravity is the only applied force acting on the comet, shouldn't all of the material,…
anonemes11
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If Alpha Centauri A's solar system exactly mirrored our own, what would we be able to detect?
Suppose there was an exact replica of our solar system 4.4 ly away (people included). What would we be able to detect and with what telescope(s)? Which planets? Could we detect radio transmissions and/or any atmospheres?
I assume detection would be…
Nick T
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5 answers
Why did the big bang not just produce a big black hole?
Questions I've often wondered about:
If all the matter and energy were concentrated at a single point at the big bang, why wasn't that a black hole, or why didn't it form one?
If the reason #1 above didn't form a black hole is one of several…
yadda
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Why do (most of) the planets rotate counterclockwise, i.e. the same way the Sun does?
Referring to the mechanisms explaining the solar system formation and to the initial rotation of the gaseous cloud that collapsed, I understand easily why the planets orbit the Sun the same way this one rotate (say counterclockwise) but I can't…
Arroway
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8 answers
Is saying that what we see of an object 1 light-year away happened 1 year "ago" in any a way useful view of the universe?
Since the speed of light is the speed of causality, the "now" state of the a faraway object for an observer should be the exact point at which its light reaches the observer, for literally all intents and purposes.
My question is whether purporting…
DoltishNeuron
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Are there any stars that orbit perpendicular to the Milky Way's galactic plane?
Most stars orbit in the Milky Way's galactic disc. But is it possible for one to orbit perpendicular to it?
Here on Earth since we're inside the galactic plane we can't get a good view of what the Milky Way looks like. But would the whole Milky Way…
user177107
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37
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Are black holes spherical during merger?
I've been thinking about black holes, specifically during the final moments before two merge. I'm wondering if black holes, or I guess more specifically their event horizons, are always spherical. It seems to me that in the moments before two…
Ryan_L
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