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Questions tagged [rotation]

Questions regarding the action of or an object rotating along an axis.

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93 votes
6 answers
9k views

Does the Sun rotate?

The planets rotate as an after effect of their creation, the dust clouds that compressed span as they did so and the inertia has kept it rotating ever since. It's fairly easy to prove that planetary ...
user avatar
46 votes
1 answer
6k views

Why does the Sun have different day lengths, but not the gas giants?

The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force ...
Allure's user avatar
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37 votes
5 answers
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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 ...
Arroway's user avatar
  • 479
31 votes
2 answers
5k views

What is the current accepted theory as to why Venus has a slow retrograde rotation?

According to this NASA overview, the planet Venus is unique (amongst the major planets), Venus has a slow retrograde axial rotation, taking 243 Earth days to make one rotation (which is longer than ...
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29 votes
1 answer
3k views

How is Uranus' north pole defined?

The rotation axis of the planet Uranus is tilted by 98° compared to its plane of orbit. This means that the north pole of Uranus is "under" the ecliptic compared to the north pole of other planets. ...
usernumber's user avatar
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27 votes
3 answers
2k views

What is the accepted theory as to why Uranus' axis is tilted so severely?

The planet Uranus is another solar system anomaly, where according to the NASA profile has an axial tilt of 97.8 degrees, also considered to be retrograde. This NASA summary "Uranus" suggests the ...
user avatar
26 votes
2 answers
26k views

Why does the Earth have a tilt of ~23°?

Is there a reason that the Earth has the tilt that it does (~23°)? How do we know which way is supposed to be 0°? Does this tilt have major consequences on the planet? Has it changed and will it ...
Jackson's user avatar
  • 557
25 votes
4 answers
6k views

Is it coincidence that the earth's rotation and revolution are in the same direction?

In a reference system where the sun is static, the rotation and revolution of the earth are, when viewed from above the north pole, both counterclockwise. Is it a coincidence that they agree? Or does ...
Marc Vaisband's user avatar
22 votes
1 answer
5k views

How did Mars come to have a 24 hour 39 minute day?

Mercury rotates three times for every two revolutions around the Sun, apparently due to a gravitational resonance with the Sun.Venus takes about 225 days to rotate, and rotates in the opposite ...
Howard Miller's user avatar
22 votes
3 answers
2k views

Why does a planet rotate and revolve?

Why do planets rotate and revolve in the universe?
M.Tarun's user avatar
  • 953
21 votes
6 answers
8k views

Are there non-rotating objects in the universe?

All celestial bodies I can think of rotate. The sun, the planets, the moon, the galaxies, clusters of galaxies, the supermassive black hole at the center if the Milky Way, accretion discs, etc. It ...
Deschele Schilder's user avatar
21 votes
1 answer
3k views

Do the axes of rotation of most stars in the Milky Way align reasonably closely with the axis of galactic rotation?

The axis of rotation of the Solar System makes a large angle of about 60 degrees relative to the axis of rotation of the Milky Way. That seems unusual - for example, most of the bodies within the ...
Roger Wood's user avatar
  • 1,359
19 votes
8 answers
10k views

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

Google says the year is exactly 365.2422 days, and so they make a leap year every 4th year, but that ends up being 365.25 days per year on average. So every 100th year they don't have a leap year, but ...
Lance's user avatar
  • 431
19 votes
1 answer
2k views

Is Earth's orbital eccentricity enough to cause even minor seasons, without axial tilt?

I was reading the answers to this question about an exoplanet having seasons without axial tilt, and several responders mention that orbital eccentricity could cause a similar effect, but that the ...
Nerrolken's user avatar
  • 637
18 votes
5 answers
9k views

If all stars rotate, why was there a theory developed that requires non-rotating stars?

According to Penrose's research, a non-rotating star would end up, after gravitational collapse, as a perfectly spherical black hole. However, every star in the universe has some kind of angular ...
Murg's user avatar
  • 937
18 votes
3 answers
5k views

How are constellations intact if the stars are rotating around galactic nuclei?

From what I understood, the Milky Way (or stars in the Milky Way) doesn't rotate like a collection of points in a disc due to the presence of some invisible matter. In theory, the angular velocities ...
Muhammed Roshan's user avatar
18 votes
4 answers
8k views

Do planets lose energy while rotating?

When a planet rotates/spins, is it true that the planet loses energy? If this is true, then where does this energy lost by the planet go? My confusion may be in the basic understanding of the ...
apk's user avatar
  • 949
18 votes
3 answers
7k views

Why don’t we feel the Earth rotating beneath us?

I’m not sure all of the details in the experiment but basically it went as follows. Someone marked their location of take off in a hot air balloon and went straight up in the air. They stayed ...
Begons18's user avatar
  • 316
18 votes
3 answers
425 views

Does the rotation of galaxies precess?

Does the axis of a galaxy as a whole "wobble" the same way that the Earth does? If so do we have any idea how much or how fast the Milky Way is doing so?
smithkm's user avatar
  • 331
17 votes
4 answers
7k views

Official degrees of earth’s rotation per day

What is the official degree to one decimal point please, of the earth’s rotation in one single day. Can it be confirmed that it is exactly 360.0 degrees using official data? Thank you in advance.
Autodidact's user avatar
17 votes
3 answers
5k views

If planets are ellipsoids why don't we have 3 diameters?

We know that each ellipsoid has 3 diameters named $2a$, $2b$, and $2c$. The Earth and all planets, in general, are ellipsoids (Saturn is the best example because it's the most oblate planet in the ...
Snack Exchange's user avatar
17 votes
3 answers
3k views

Shape of neutron stars

I've heard that the more an object spins, the less of a true sphere it is. Using this logic most of neutron stars would be far from spherical,in general what shape are most neutron stars?
kingW3's user avatar
  • 465
15 votes
2 answers
2k views

What is the evidence that galaxies rotate?

Do all galaxies rotate? If so, do they rotate in the same direction? What observations have been made of galaxy rotation?
user avatar
14 votes
1 answer
3k views

Earth is Tilted, but in reference to What Object / relative to what?

I am asking basic question on trying to understand on tilt. I know if I (as a human) tilt when standing on feet, my tilt will be in relation to gravity. For Earth, I am not able to understand, what is ...
puzzled's user avatar
  • 607
14 votes
4 answers
3k views

Would an exoplanet without axial tilt have no seasons?

Would an Earth analog exoplanet which rotates around a solar analog, but without axial tilt, have no seasons? Would it be similar to how Los Angeles does not have very noticeable seasons compared to ...
seijitsu's user avatar
  • 403
14 votes
2 answers
724 views

What is the difference between the Yarkovsky effect and YORP effect?

As far as I understand, both the Yarkovsky effect and the Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect exert forces upon bodies as a result of thermal photon radiation. How do both effects ...
Nick Silvestri's user avatar
14 votes
2 answers
19k views

If Earth didn't rotate, would we feel heavier? [closed]

Suppose the Earth's rotation slowed for some reason. Would the lack of centrifugal force cause us to feel heavier than normal? Likewise, if Earth's rotation increased, would we feel lighter as ...
Spinmeister P's user avatar
13 votes
4 answers
6k views

How can we avoid needing a leap year/second?

Given the Earth's current speed around the sun and current rate & axis of rotation, what is the best way to keep time to avoid a leap year? How many hours should we have in the day and days in a ...
TheSmallestOne's user avatar
13 votes
1 answer
2k views

How is it possible for a collision to be responsible for Uranus's axial tilt?

I realize that the collision explanation is in any case highly (purely?) speculative, but I'm curious how it would work. If Uranus is a ball of gas, why wouldn't any colliding object just pass ...
Kurt Weber's user avatar
13 votes
1 answer
1k views

Are galaxies growing, shrinking or stable?

When I look at spiral galaxies they look a bit like the whirlpool of water going down a sink and I wonder if eventually they shrink to a small point (or a giant black hole?). On the other hand they ...
KDP's user avatar
  • 373
13 votes
4 answers
15k views

Do solstices and equinoxes shift over time?

Right now, I think the winter solstice is around December 21. Has it always been around this date constantly? Since the earth's axis's 23.45° tilt will be on the exact opposite side in 13000 years (...
Mickael Caruso's user avatar
13 votes
2 answers
2k views

Cancelling out earth rotation speed, Altazimuth mount

I have a Dobsonian telescope. It is using Altazimuth mount. Basic idea of using it is to target the object by moving telescope vertical axis perpendicular to the ground, and an elevation axis that is ...
Kocur4d's user avatar
  • 233
12 votes
4 answers
1k views

Why do planets tend to rotate in the same direction although they have formed from tumbling asteroids?

The axial tilts of asteroids seem to vary randomly (let me know if this premise is wrong), while the planets have a strong tendency to rotate in the same way. If planets were formed by colliding ...
LocalFluff's user avatar
  • 11.4k
12 votes
1 answer
2k views

What rotational speed would Mercury need to have to achieve a temperature comfortable for humans

I wondered what rotational speed would Mercury need to have to achieve a temperature comfortable to humans, let's say 20 °C. EDIT: My idea was that if Mercury is so cold on the night side and so hot ...
Piotr Golacki's user avatar
12 votes
3 answers
7k views

Why isn't Earth a perfect sphere? [closed]

In general, almost everyone describes Earth as an perfect sphere, but in reality it isn't a perfect sphere. Is there any specific reason why Earth is not perfect sphere ?
Hash's user avatar
  • 221
12 votes
2 answers
17k views

What is the fastest spinning rotation of a Neutron star?

What is the fastest spinning rotation of a Neutron star? I have heard that Neutron stars have a specially fast spinning rotation. What is the fastest?
Jamd's user avatar
  • 377
11 votes
2 answers
3k views

How scientists find the direction of rotation of planets?

How do we know that Mercury, Earth, Mars, Jupiter, Saturn, and Neptune rotate counterclockwise and Venus, Uranus, and Pluto rotate clockwise? How do scientists determine the direction of rotation of ...
apk's user avatar
  • 949
11 votes
2 answers
579 views

How do we know that an exoplanet is tidally locked to the parent star?

Often in discussing exoplanets we hear that they are close to the parent star (usually a red dwarf) but then there's a caveat that the planet is tidally locked to that star and that that fact severely ...
stackzebra's user avatar
  • 1,449
11 votes
4 answers
10k views

Why is twilight longer in summer than winter and shortest at the equinox

I recently decided to set my alarm clock to wake me up when it is "dark" out. In the end, I decided to set my clock to the earliest time that nautical sunrise is in my state (Illinois) and stick with ...
firebush's user avatar
  • 231
11 votes
1 answer
538 views

How does a star's rotation affect a star on the main sequence?

I searched and have found that the questions mainly focus on neutron stars, white dwarfs and black holes. This was not what I want. Basically, the bigger the star's mass is, the more intense its ...
Christmas Snow's user avatar
10 votes
3 answers
3k views

Why does a timelapse video of a stationary Milky Way make the horizon appear to move from horizontal to vertical?

In this video, with a rotating camera keeping the Milky Way 'stationary,' the horizon appears to transition form horizontal to nearly vertical. I understand the Earth ...
99Gretzky99's user avatar
10 votes
2 answers
3k views

Why do certain moons have their rotational period equal to their orbital period?

Our moon and Saturn's moon, Titan, have this feature. Because of this we only observe one side (hemispere) of our moon. Why is this? What is the Newtonian or astrophysics that would explain this? ...
0tyranny0poverty's user avatar
10 votes
1 answer
818 views

Which of the exoplanets are having retrograde rotation?

By exoplanet, I mean planets outside of our solar system(i.e., planets in other solar systems). If we talk about our solar system, then Venus, Uranus, and Pluto have retrograde rotation. Most of the ...
apk's user avatar
  • 949
10 votes
3 answers
1k views

How can the Earth's rotation speed up? [closed]

It is known as a fact that Earth's rotation is slowing every year, that's why we sometimes have 61 seconds long minutes. In the Java documentation of Time : http://docs.oracle.com/javase/7/docs/api/...
Fabinout's user avatar
  • 211
10 votes
1 answer
586 views

Why does Saturn have a more prominent equatorial bulge and higher flattening ratio than Jupiter despite rotating slower?

It is my understanding that a planet's equatorial bulge is caused by the centrifugal force produced by its rotation, and the faster a planet rotates the bigger the bulge and flattening ratio of a ...
user177107's user avatar
  • 2,699
10 votes
1 answer
16k views

How would Earth's climate differ if it's axis were tilted around 90 degrees like Uranus? [closed]

As the title states, what would the effect on Earth's climate be if it's axis were tilted approximately 90 degrees like Uranus? I'm specifically wondering about the effects on seasons, temperature, ...
Fezter's user avatar
  • 527
9 votes
4 answers
2k views

Is there any difference between tidal locking and synchronous rotation?

I'm trying to understand more about orbital mechanics, and I'm encountering a few terms which I'm not sure if they are exactly the same. The two terms are Tidal Locking and Synchronous Rotation. To my ...
ValientProcess's user avatar
9 votes
3 answers
3k views

Why do our clocks not go out of sync with the day over a year?

Our clocks use 24 hours for a day, our planet takes 24 hours to rotate completely and our planet revolves around the sun in 365 days. Imagine at the start of the year, the side of Earth facing Sol is '...
JamEngulfer's user avatar
9 votes
2 answers
1k views

Decreasing rate of Earth's rotation: where does the power go?

I understand from Wikipedia that, "The length of the day, which has increased over the long term of Earth's history due to tidal effects, ...". If the angular velocity of the earth is decreasing then ...
scorpdaddy's user avatar
9 votes
1 answer
1k views

Do some comets spin? If so, how fast?

The GIF below is copied from my question earlier What might a CN filter be in the context of comet watching? Is it showing dust, or gas, or something else? where I'd said: In this post on the website ...
uhoh's user avatar
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