Questions on astronomical objects orbiting a star massive enough to be rounded, not massive enough to cause fusion, and which have cleared its orbit of planetesimals.

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Have any co-orbital exoplanet pairs been discovered (and not subsequently retracted)?

For this question, I think a good working definition of co-orbital configuration would be two bodies orbiting around a third much larger body in a 1:1 resonance and where neither mass is negligible. ...
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1answer
1k views

Why do the planets orbit in the same direction?

Theoretically, planets would have an approximately equal chance of going one way in their orbit or another but in reality, this is not the case (at least in our solar system). Why is this?
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1answer
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Would a viewer see Earth from the rim of Shackleton Crater?

I've been researching this but so far have not found an answer. If you were standing on the top of the rim of Shackleton Crater at the lunar south pole, would you be able to see any of Earth? I can't ...
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1answer
51 views

Distance and orbital period for terrestrial binary planets

This article, http://phys.org/news/2014-12-binary-terrestrial-planets.html, suggests binary planets could orbit each other at a distance of only three planet radii. For two earth-like planets, that is ...
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3answers
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Is extraterrestrial mining more difficult or impractical for bodies without plate tectonics?

This article talks about the possibility of mining Uranium on the moon. Since the Moon lacks the geological forces that have created veins of concentrated minerals on Earth, would extraterrestrial ...
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2answers
94 views

Could this three moons system be stable?

In my fictional world I have selected all parameters to maximize the Hills Sphere of my planet. The planet has three times Earth's mass and it is located in 2 AU from its star that's 1.4 times more ...
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0answers
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What are the requirements to become a planet? [duplicate]

A planet is taught to us (at primary school) as a ball of rock that orbits around the Sun and is similar to our own planet, Earth (in as a ball of rock). But of course, humans have to be more specific ...
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3answers
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How many planets are there in this solar system?

So, in school (that's a long time age) they have been teaching us there are 9 planets in our solar system. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto But every now and then I ...
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2answers
136 views

Advancement of perihelion, data

I was looking for accurate and up-to-date data regarding the advancement of the perihelion of the planets in the Solar System, the only ones I've found so far are at least 90 years old bout I really ...
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31 views

Question on retrograde motion [duplicate]

I am a beginner Does planets exhibit retrograde motion (eg Mercury and Venus) only because of earth rotation? Or is there any other reason? Please clarify
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2answers
107 views

If the planets only attract, then how can they stay in their orbit?

Gravity is related to mass, and gravity is an attracting force on every body. Then what happens when bodies only attract each other..without repulsion they may strike the sun. I think there must be a ...
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2answers
94 views

What is the effect of the axial precession on the orientation of the planet's orbits?

I am working on an online application to visualize the positions of the planets and to calculate their ephemerides (you find it here, but it is not complete yet). I do not have much knowledge in ...
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1answer
78 views

Can a gas giant be hollow?

Let's think of Saturn, because of its density. Can there be a place near the center of the planet where the gravity upwards is more than towards the center, and with an atmosphere that is more ...
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2answers
207 views

Confirm: We can only notice planets if their orbit passes in front of their star and our view

If we can tell a planet exists by the dimming of the brightness of a star when it passes in front of our view of the star does that mean we cannot see a planet if it does not cross in front of our ...
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1answer
54 views

What causes celestial bodies to move like they do from Earth's surface?

As you probably know, the planets have pretty predictable orbits around the sun but what exactly causes the complex movement of celestial bodies in the sky from Earth's surface? Mars is an excellent ...
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2answers
2k views

Could the 9th planet be virtual?

Astronomers recently claim that there is evidence for a 9th planet. As far as I understood it, this is mainly based on coinciding orbital parameters of a few Kuiper belt objects. Could the 9th planet ...
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2answers
138 views

What's the name for [the other kind of planet] in a binary star system?

This XKCD what-if talks about rainbows on planets in a binary star system. It points out that there are two types: circumbinary planets, where the planet orbits far from and around both stars [...
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2answers
132 views

any unique phenomenon when the cores of two planets are aligned with their star's core?

Imagine a line passing through the cores of two planets (in the same planetary system) and their star. Have we ever witnessed this - either with both planets on the same side of the star or on ...
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3answers
113 views

How do we know that other planetary systems aren't composed of antimatter? [duplicate]

How do we know that other planetary systems aren't composed of antimatter? If they never touch matter, then they don't annihilate. All their observable physics (spectra) are the same as matter, right?
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Resources on planetary stability

I am a fifth (and last) year undergraduate student in Physics with good level of Mathematics formation and basic Astrophysics formation. I recently read some theories about Solar System formation and ...
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39 views

How much heat emanates from the planets after formation?

The 2nd answer to this question by MBR got me thinking about this. Is there some general guideline for residual heat a planet should emit, say 4.5 billion years after formation. I'm defining heat ...
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1answer
328 views

Which is the largest planet ever observed?

I don't know much about planets outside our solar system. Do we even know the limit of the size of how large a planet or satellite can be? The largest planet I know of is Jupiter, but could there be ...
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2answers
69 views

How does large body gravity affect planet formation?

If Jupiter's gravity is what kept the asteroid belt from forming a planet, then why didn't the sun's gravity keep the inner planets from forming?
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DUT time offsets to UTC [duplicate]

Astronomic observations in geodesy. It is well understood that sun and star positions may be expressed in Greenwich hour angle and declination. Or Right Ascension Declination. And may be published ...
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2answers
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Retrograde motion of planets: reason and time?

I am a beginner. I'd like to understand how planets (except Sun and Moon) exhibit retrograde motion. When does the retrograde motion start for a planet (eg Mars) and how long (time limit) planets ...
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4answers
301 views

How are rogue planets discovered?

Planets are usually found by observing a star and waiting for the light level to drop when a planet passes in front of it, but what about rogue planets that don't have host stars?
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93 views

Does earth have retrograde motion?

I am a beginner. Please let me know whether earth has retrograde motion If it does not, let me know the reason
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190 views

Which Planet/Star is it?

I live in north India. About 24° latitude. I can see a very Bright star in sky. Its towards east and high up. Is it Venus , Jupiter, star or anything else? Its not Sirius. I used Orion belt for that. ...
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Does the gravity of the planets affect the orbit of other planets in our solar system?

When one planet passes near another during its trip around the sun, does their gravitational pull is strong enough to disrupt noticeably each other's orbit ?
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3answers
208 views

Why do the gas giants in the Solar System have comparatively large orbits compared to the inner planets?

Ever since I observed the depictions of the Solar System, I was obsessed with the question of why the gas giants (outer planets) have very large orbits, compared to the planets that are closer to the ...
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2answers
169 views

What is the fifth moon-like object I saw around jupiter through my telescope?

Tonight while observing Jupiter I was able to see a five (what looked like) moons. I have observed Jupiter often before and only been able to make out the four galilean moons. It's my understanding ...
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1answer
82 views

How to calculate a planet's apparent size when the planet is viewed from a moon in orbit around it?

Specifically in this case, how large would Jupiter be seen in the Io's sky in comparison to the moon in the Earth's sky? How to calculate this? Also, if somebody knows any online software which lets ...
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5answers
5k views

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 ...
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1answer
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Can dark matter be found in the shape of planets, galaxies etc.?

If dark matter has gravity just like normal matter, does that mean it can also form planets, solar systems and so on? Any answer will be appreciated.
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What planet is better than earth to infer solar system configuration?

The mankind had to work some centuries to infer the real configuration of solar system, starting from greeks, Ptolemeus, until Copernicus, Galilei, Kepler, Newton etc. Is there any planet where we ...
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2answers
257 views

Can there be an object with planetary discriminant between Ceres and Neptune?

The planetary discriminant is a measure of how dominant a body is within its region of the solar system. For (true) planets, it is $>10000$ and for dwarf planets it is $<1$. (See this answer to "...
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3answers
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Did I see another planet?

A couple days ago, I zoomed in with my 30x optical zoom camera, and after some exposure adjustments, a bright star in the night sky turned into this: Are those other planets or other stars? Or is ...
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1answer
102 views

Why are planets round?

I was studying our solar system and all celestial objects are depicted as round objects, including black holes.. worm holes as hollow cylinders as a pathway across two universes.. even the galaxy is ...
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131 views

Number of stars & planets in Milky Way Galaxy?

Is there any specific numbers on stars & planets count on Milky Way Galaxy ?
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Why is the universe full of spinning objects?

Almost all celestial objects are rotating in some way about their axes. Why is this and should we expect the rotation to slow as the universe ages?
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1answer
67 views

Is it possible to know if a planet is located in the Habitable Zone knowing it's properties?

Is there an equation that can give me the possibile distance of the planet from his star knowing planet's temperature (or other datas)? I found this method for calculating the Habitable Zone but it'...
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1answer
61 views

Can we apply Kepler's law of planetary motion to the moons motion around the earth?

I have been trying to understand Kepler's law of planetary motion for a while. So I was thinking, if it would even apply to the moon orbiting around the earth. Does the moon too orbit in an ellipse ...
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2answers
146 views

Could a star revolve around a planet? [duplicate]

They actually do, but let's set Relativity aside for a moment. And the whole barycenter thing too. Here's the scenario: Somewhere in the backwaters of a galaxy there is this huge planet. It is NOT a ...
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2answers
536 views

the most accurate system that can show the positions of planets at my birthday [closed]

My birthday : 4 December 1982 If you have such astronomical calculator on your computer please send me the result ! Alternatively if you know an online astronomical service for my purpose please ...
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1answer
104 views

Theoretically, can a solar system evolve around lagrange points

My question is, during the evolution of a solar system is it possible to end up with a massive planet around a star with two small planets around their $L_4$ and $L_5$. Since we know it is not ...
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2answers
98 views

Color of planets

I am developing an astronomy software and need to know the color of each planet in the Solar System, when observed with the naked eye. I cannot find that information after googling for a while. Is ...
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23 views

Convergence of galaxies [duplicate]

What would happen to Earth and other planets after about millions of years at the time of convergence of milky way galaxy with andromeda galaxy? (Supposing the planets and the sun are still there and ...
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2answers
268 views

Who gets to name Planet Nine if it is confirmed?

According to Wikipedia, "On 20 January 2016, researchers Konstantin Batygin and Michael E. Brown at Caltech announced calculation-based evidence of a massive ninth planet in the Solar System." If ...
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2answers
117 views

What planets and moons have we seeded with life (if any)?

Which planets and moons have we accidentally (or purposely) seeded with life? I would expect this to be any planet or moon we have sent an unsterilized (or not fully sterilized) lander to, or crashed ...
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184 views

Best planets profile for a tattoo of the solar system [closed]

I want to get a tattoo of the solar system. The gap between the planets should not be preserved and the differences in sizes will only be symbolic. I found the following My question is if all stars ...