Questions tagged [planet]

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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58 votes
6 answers
7k views

Why hasn't the "9th Planet" been detected already?

In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask ...
22 votes
3 answers
2k views

Why does a planet rotate and revolve?

Why do planets rotate and revolve in the universe?
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38 votes
5 answers
15k views

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 ...
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36 votes
1 answer
9k views

Why do the planets in our solar system orbit in the same plane?

(Yes I'm excluding Pluto from this the same way it was excluded for not being a planet) Observing the planets orbit of the Sun they all seem relatively planar and roughly all orbit along the same ...
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59 votes
7 answers
38k views

How many planets are there in this solar system?

So, in school (that's a long time ago) 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 keep ...
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12 votes
2 answers
45k views

How to calculate the expected surface temperature of a planet

I'm writing a program to generate solar systems but I'm having trouble calculating the expected temperature of a planet. I have found a formula to calculate this, but I haven't been able to get a ...
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37 votes
5 answers
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 ...
5 votes
1 answer
247 views

What causes "North-South ambiguity" when doppler radar imaging a planet surface equator?

I'm having a hard time understanding why there would be this ambiguity. Also, why would this be not the case if the planet was viewed pole on? Edit: "North South ambiguity" is a term used in ...
21 votes
6 answers
9k views

Does this smartphone photo show Mars just below the Sun?

I live in Essex, England (51.7678° N, 0.0878° E). On 25 July 2019 (hottest day ever in the UK, btw), 06:43 BST, I took this smartphone photo of the Sun. Is that white dot just below and left of the ...
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21 votes
4 answers
4k views

Why are orbits elliptical instead of circular?

Why do planets rotate around a star in a specific elliptical orbit with the star at one of it's foci? Why isn't the orbit a circle?
9 votes
4 answers
1k 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?
19 votes
2 answers
1k views

What physical features determine if a planet is a major, minor or dwarf planet?

Like many, when I was growing up, we always were taught, hence always learned that there were 9 planets. However, recently, decisions were made and all of a sudden there were 8 major planets and a ...
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13 votes
3 answers
693 views

Why are planets spherical?

I am a complete novice when it comes to astronomy, but someone asked me the above question casually. It seems as though planets are all roughly spherical, whereas other celestial bodies aren't ...
11 votes
3 answers
4k views

Compute Planet's Apparent Visual Magnitude

In a hypothetical solar system there exist: a sun of radius $r_s$ and absolute visual magnitude $V$ the Earth, with radius $r_e$ and distance from the sun of $1\,AU$ another planet, wit radius $r_p$, ...
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2 votes
1 answer
378 views

How did early estimates of a "potato radius" set 1 eV ~ GMμ/R and get 200 to 300 km?

@DavidHammen's answer explains that Goblin has roughly a potato radius and I can't believe I just wrote Goblin and potato in a serious question. That happened. The linked paper; The Potato Radius: a ...
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16 votes
2 answers
904 views

Open problems in astronomy that an amateur (with a PhD in some other field) would have a chance of solving?

What are some open problems in astronomy that an amateur would have a chance of solving? Suppose the amateur has a PhD in some other field, owns a basic telescope, a set of filters, diffraction ...
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17 votes
5 answers
3k views

When will all eight planets in our solar system align?

Ignoring expansion of the universe, entropy, decaying orbits, and interference from any bodies colliding with or otherwise interfering with their orbits, will the eight planets known planets in our ...
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12 votes
4 answers
3k views

Could Neptune be viewed with the naked eye from Uranus?

Which star or planet in our night sky can match what Neptune would look like when viewed from Uranus, or one of its moons? The answer would be for the most favourable condition, which is when Neptune ...
17 votes
1 answer
729 views

Can the paper narrowing Solar System's barycentre to within 100m help find Planet Nine?

I've just read this recent news article, Astronomers Have Located The Centre of The Solar System to Within 100 Metres, reporting on a paper[1] that claims narrowing the Solar System barycentre to ...
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14 votes
5 answers
10k views

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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5 votes
3 answers
1k views

Why do stars twinkle but planets don't [duplicate]

Many people say that stars twinkle because of Earth's atmosphere. However, the atmosphere is still there when we look at planets and don't see they twinkling. Is there a clear scientific consensual ...
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3 votes
1 answer
400 views

Why are planets round? [duplicate]

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 ...
3 votes
1 answer
195 views

Why don't we detect planets around OB stars and no terrestrial planets around A or early F stars?

Looking at an exoplanet database, I noticed that there are very few planets detected around main-sequence OBA stars, and most of them are gas giants/brown dwarfs. Why can't we detect low-mass planets ...
24 votes
6 answers
3k views

What makes protoplanetary disks start rotating? (Initial energy needed to rotate)

Planets form from a protoplanetary disk that has been rotating around its star. The initial energy that makes them rotate really matters to me. Why did the protoplanetary disk start rotating around ...
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27 votes
1 answer
1k views

Why do planets and satellites in the Solar system look so wildly different if they came from more or less the same matter?

First, the planets. We have Mercury, which is rocky, no atmosphere. But then we have Venus, which is completely different: thick atmosphere, very hot, geologically active. Then Earth - blue, full of ...
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24 votes
4 answers
4k views

Is there a upper limit to the number of planets orbiting a star?

Our sun has 8 planets orbiting as well as a number of dwarf planets. Are there any calculations that hint as to whether this number is close to some theoretical maximum value or are we simply an ...
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9 votes
3 answers
3k views

Is Jupiter a dwarf planet?

I know the question seems silly, but as far as I've understood, is this the definition of a dwarf planet: circling around a star, and not being a star itself having a round shape (otherwise every ...
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18 votes
1 answer
483 views

How did scientists determine an estimate of the number of planets greater than Sedna's size to exist in the Inner Oort Cloud?

In the article, New Dwarf Planet Found at Solar System's Edge, Hints at Possible Faraway 'Planet X' (Wall, 2014) where they report on research and observations performed by astronomers that discovered ...
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15 votes
3 answers
2k views

What wavelength to best detect the "9th planet"?

We know that the reflected sunlight will make detecting the 9th planet very difficult in the visible light. Is there another band that will be more likely to detect it? What is the surface temperature ...
8 votes
4 answers
6k views

Are there any known planets whose axis is oriented such that one pole always faces its star?

Earth rotates around the sun and around its axis (A North, South axis) giving us days, nights and seasons. Are there any known planets that rotate with an axis pointing toward its sun so that one ...
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5 votes
2 answers
1k 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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3 votes
1 answer
583 views

What is the distance of Earth from the 7 planets, moons and the Sun at a point of time?

I wanted to know the distance of the 7 planets (Mercury, Mars, Venus, Jupiter, Saturn, Uranus, Neptune ) each (or at least 5 planets) from the earth and the angle that it will make with a line ...
16 votes
1 answer
464 views

Orbital velocity of a planet - why is my calculation off by about 10%?

I am not sure if I am doing something wrong, or misunderstanding Reider and Kenworthy (2016). I'm just trying to reproduce the orbital velocities listed in Table 1. The second paragraph of Section II ...
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9 votes
1 answer
2k views

How small can a planet be and still have Earth-like gravity?

A planet made from denser material than Earth might have equal gravity to Earth but a smaller radius. How small can a planet be and still have Earth gravity? Ideally it should be habitable by humans, ...
9 votes
3 answers
16k views

Years, months, days, and ... weeks?

Why do we divide time into weeks? Is there any celestial reason why humans do this? one year: earth revolution around the sun one month: moon revolution around the earth one week: 7 days = ??? ...
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9 votes
1 answer
450 views

3 years later, how strong is the evidence for planet 9?

I came across post in quora where somebody said that "most astronomers no longer think Planet 9 exists" and being somewhat shocked by that, I did a google search and found a fairly recent article that ...
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7 votes
2 answers
548 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 [the ...
4 votes
1 answer
3k views

Planets classification by density

In our Solar system, the density of major planets varies from 0.7 g/cm3 (Saturn) to 5.5 g/cm3 (Earth). For exoplanets, the density varies from very low (0.03 g/cm3 for Kepler-51x) to very high (77.7 ...
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4 votes
1 answer
442 views

Brown dwarfs and planets

As far as I know, a brown dwarf is a 'star' whose core never underwent a fusion reaction, so it never became a star. So I was wondering if, apart from orbiting a star, is there any difference ...
3 votes
2 answers
999 views

What is the axial tilt of a planet measured relative to?

I am very much a beginner on the astronomy front but I understand about planets having different axial tilts, hence why Venus turns the opposite direction from the Earth and Uranus turns sideways. ...
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3 votes
1 answer
608 views

Equations for coordinates of solar system objects

I would like to write a program that visualizes the solar system. To do this, I would need equations for calculating the coordinates of each solar system object at a given time. Where could I obtain ...
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3 votes
1 answer
207 views

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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3 votes
1 answer
335 views

Any cheap (less than 100 euro) telescope for observing Jupiter? [closed]

The moon is not challenging. I would like to observe the big planets and their rings.
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2 votes
1 answer
320 views

How to calculate the orientation of planets at current epoch

For an application I am working on I am creating a simulation of the solar system. In this simulation, a user needs to be able to 'move' to any position on any planet, and have the sky be accurately ...
2 votes
2 answers
2k views

What would happen if a planet is removed from the solar system? [closed]

More exactly what would to happen to us/Earth in general if any of the gas giants is removed by magic from the solar system ? How long would it take after such change before we notice it ? How major ...
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1 vote
2 answers
12k views

what magnification is required to see jupiter, saturn, venus and mars with a 50mm refractor scope with f/12 ratio and 600mm focal lenth

i have a beginner telescope of 50mm and want to see planets it is arefractor with f/12 ratio and two eyepieces of 5mm and 10mm and i want to see mars, Jupiter, Saturn and venus. my max zoom ix 120x ...
13 votes
1 answer
428 views

Changes to Earth's orbit

Any time a spacecraft comes in close proximity to a planet and if the spacecraft has the right angle then it is able to use the planet's velocity to move itself further into space. According to ...
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9 votes
1 answer
401 views

How was the hypothetical ninth planet kicked so far out of the Solar System?

I was reading this article on science news and ran into the following statement: Such a remote super-Earth probably originated closer to the sun only to be kicked out by the other giant planets ...
8 votes
1 answer
152 views

"Pluto Time" for any solar system body

A while back NASA made a site called Pluto Time, where you can enter your address and find that "...moment near dawn and dusk each day, where the illumination on Earth matches that of high noon on ...
3 votes
2 answers
255 views

A few questions regarding the transit of planets

Here we will be concerning ourselves with the transit of a planet with it's parent sun. I have a few questions that I am not sure about: 1) Do all planets transit their parent sun? It would seem to ...
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