All Questions
Tagged with celestial-mechanics planets
70
questions
33
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7k
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Is there a maximum distance from a planet that a moon can orbit?
Given a planet that orbits a star, and a moon that orbits that planet, is it possible to define a maximum orbital radius of that moon, beyond which the moon would no longer orbit the planet, but the ...
- 49.9k
0
votes
1
answer
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Estimate Saturn's mass [closed]
How can you estimate Saturn's mass using data from Cassini's final moments in September 2017 (apoapsis on September 12 at 1:27 a.m. EDT Saturn time at a distance of about $1.3*10^6$ km from Saturn, ...
- 2,728
9
votes
4
answers
2k
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Binary Star system with one star stationary?
Can a Binary Star system be possible where in one star is stationary and the other star revolves around it? (Just like a planet revolving a star. i.e planets in the system and the star revolving ...
- 1,616
2
votes
2
answers
284
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How to measure the ratio of a planet's radius to a star?
I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information.
One of ...
- 46.1k
16
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6
answers
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If another planet was opposite Earth, would we be able to observe it?
Imagine another Earth-sized planet, in the exact same orbit as Earth, but 180 degrees out-of-phase. In this arrangement, at all times, you would be able to draw a single straight line through space ...
- 204
3
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3
answers
203
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Can a planet have multiple significant sized moons?
The Earth has one moon at about 1/80 of Earth's mass. Is it possible to have two moons large enough each to subtend a >30 minute disk as viewed from the surface?
I have tried with various ...
- 3,440
3
votes
3
answers
183
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Why do the planets tend to spin in the same direction as they orbit the center sun?
I mean, why do the spin angular momentum and the orbit angular momentum of a planet tend to have the same direction?
As we all know, a planetesimal $m$ orbiting a sun with mass $M_{sun}$ at $r$ will ...
- 2,712
1
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2
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Is it possible to determine if a planet can have a moon based on its mass and gravitational pull?
I'm curious, if based on what we know with Newton's law, can we determine if a random planet, knowing it's mass and gravitational pull, can hold a moon in it's orbit.
Or to phrase it another way, is ...
- 6,362
0
votes
2
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741
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Planet in which satellite (moon) and star (sun) appear together once a year
With a hypothetical system, where the moon would be always on the opposite side of the planet than the sun, in a way that the moon would only be visible at night on the planet.
I don't know if this ...
- 207k
0
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2
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292
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How does Kepler's Second Law show that a planet further from the sun will move slower?
This is probably a very stupid question. We are told that due to Kepler's Second Law, which according to this very straightforward explanation:
"Kepler's second law of planetary motion describes ...
- 207k
0
votes
3
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366
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Are moons always smaller than the planets they orbit?
I'm not a physicist, asking for knowledge. Is there any moon orbiting a planet, but bigger than that planet? If not, is it mathematically possible for a bigger object to orbit around a smaller object ...
- 21.4k
1
vote
2
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150
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Ptolemaic system parameters
I recently learned about the Ptolemaic system, which seems pretty accurate. There is even a simulator on the Internet: https://astro.unl.edu/naap/ssm/animations/ptolemaic.html
You can see that there ...
- 11.7k
0
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0
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43
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Why are the orbit of planets usually ellipses? [duplicate]
There has been a similar question about planets' orbits being ellipses but the answer circulates around how the circle is a special type of orbit which doesn't really answer my question.
Elaborate ...
- 207k
2
votes
1
answer
230
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Angular momentum of a planet about apogee
Angular momentum of a planet about its apogee is maximum at __________
Now, I do know that
Angular momentum of a planet around the focus of the elliptical orbit (the sun) is conserved due to gravity ...
- 207k
29
votes
6
answers
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Why are the orbits of planets in the Solar System nearly circular?
Except for Mercury, the planets in the Solar System have very small eccentricities.
Is this property special to the Solar System? Wikipedia states:
Most exoplanets with orbital periods of 20 days ...
- 207k