Questions tagged [rotation]

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

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Can the pebbles growth model be applied to the rotations of planetary systems? [duplicate]

I've just read the University of Amsterdam 2019 News item Pebbles determine the direction in which planets rotate (which links to R.G.Visser et al (2020) Spinning up planetary bodies by pebble ...
Deschele Schilder's user avatar
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1 answer
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When will Mercury have rotated an extra round around its axis?

It is well known that Mercury orbits slightly differently from a pure Newtonian orbit. Every year a slight deviation is found. Now if we observe a lot of these orbits then Mercury should at one point ...
Deschele Schilder's user avatar
22 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
18 votes
3 answers
4k 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
1 vote
1 answer
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App Stellarium and hourly wobbling motion of Neptune

In Stellarium when I zoom in on Neptune to be able to see your daily rotation. I select Neptune, center it (space bar) and then make increments of one solar hour (command +). I notice that the axis ...
Dante_Astroboy's user avatar
2 votes
1 answer
95 views

Does precession affect this measurement?

I don't have the astronomy vocabulary to ask this question. You can find a better picture at https://www.timeanddate.com/astronomy/axial-tilt-obliquity.html. I want to know if the distance between ...
Bookaholic's user avatar
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Converting Invariable plane to J2000 ecliptic

I've been following the answer given by Mike G here: How to calculate the orientation of planets at current epoch to get planets to have the correct orientation in my program, but all the angles are ...
nussun's user avatar
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4 votes
1 answer
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How galactic density falls using Oort constants

I am given the observations that Oort constants $A$ and $B$ are, respectively: $14.5 \text{km s}^{-1} \text{kpc}^{-1}$ and $-12 \text{km s}^{-1} \text{kpc}^{-1}$. From these, I am supposed to conclude ...
zabop's user avatar
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1 answer
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How would one estimate the rotation period of a star from its spectrum?

The figure is shown; the measurements were taken on two consecutive observing nights. The Ordinate is the flux normalized to continuum and the abscissa is the wavelength scale. You can see the "...
Jay D's user avatar
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can i use heliocentric velocity as a rotation speed? [closed]

In the research of the galaxies, does heliocentric velocity involves space's expanding velocity? and can i use heliocentric velocity by galaxy's rotation speed?
INHYUK PARK's user avatar
4 votes
1 answer
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Astrophysical black holes deviating from Kerr black holes?

Rotating black holes are formed due to the gravitational collapse of massive spinning objects. And, it is generally believed that Kerr black hole solutions are valid for the empty space outside of the ...
Ad Astra's user avatar
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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
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Accelerations on the Moon due to its orbit and its spin

A gyroscope is placed on the equator of the Moon. It detects among others 2 accelerations: one due to the orbit and one due to the spin. What is the module of the second one compared to the first one? ...
Gilbert Vidal's user avatar
6 votes
0 answers
151 views

How was the axial tilt of planets measured?

https://en.wikipedia.org/wiki/Axial_tilt#Solar_System_bodies gives the axial tilt of all planets with two decimal precision, but how and when were they measured so precisely ? I guess it's "easy&...
Dr. Goulu's user avatar
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How fast do the poles of Jupiter and Saturn precess?

As Jupiter and Saturn have very fast rotation periods, about 10 and 11 hours, respectively, I am assuming that their poles will precess much faster then Earth. Since Earth's poles precess every 26000 ...
WarpPrime's user avatar
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9 votes
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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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Will there be any more planets come into our solar system and make it their "home"?

Could we have more planets come into our system and get trapped by our suns gravitational field and rotate?
TheBigJoe1489's user avatar
6 votes
3 answers
9k views

Will Earth rotate backwards in the future?

Hello recently I heave heard the earth will eventually start rotating in the opposite direction (ie sunrise from the west) . I am not sure if this is true, but a lot of sites are claiming it to be ...
X caliber's user avatar
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2 votes
1 answer
124 views

Calculating the Solar Day of an Exoplanet?

I am currently in the process of compiling a list of stars and their planets, given the information in the European Star Catalogue found here, but I'm struggling to find out how to calculate a planets ...
OmniOwl's user avatar
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4 votes
1 answer
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What is the YORP effect exactly? Is it just the non-central component of the Yarkovsky effect?

This answer to Where have all the Vulcanoids gone? links to the aptly-titled The YORP Effect Can Efficiently Destroy 100 Kilometer Planetesimals At The Inner Edge Of The Solar System which says in ...
uhoh's user avatar
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Is a three body gravitating system doomed to collapse?

Suppose we have two gravitating bodies, which are rotating around each other. They are bodies and are affected by deformation caused by tidal forces. Moving tidal waves suck energy from the axial ...
Askold Ilvento's user avatar
5 votes
1 answer
185 views

Are there any bodies in the solar system whose rotation is almost tidally locked or barely tidally locked?

The Moon's rotation is firmly tidally locked to the Earth and the Earth's rotation is firmly tidally unlocked with respect to the Moon. I gather that Mercury's rotation is tidally locked in a 3:2 ...
Roger Wood's user avatar
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21 votes
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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
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Third rotational angle in equatorial coordinates

Right ascension and declination identify an object's position in the sky, but if we are looking at something through a telescope, there is a third angle of interest, namely how our view is rotated ...
Doguleez's user avatar
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2 votes
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What should be the "poles" for irregular shaped bodies?

Continuation of: What is the definition of a "pole" of a celestial body? uhoh's answer says that distinct bodies should have a center of mass. If the body is spherical, then the COM will be ...
Nilay Ghosh's user avatar
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6 votes
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What is the definition of a "pole" of a celestial body?

What is the definition of a "pole" of a celestial body? Earth's pole is defined as it's rotational pole. The North and South Poles are the two points on Earth where its axis of rotation ...
cowlinator's user avatar
1 vote
0 answers
46 views

Is there an API to obtain Solar System body axial tilt data?

I would like to get information about rotation period and axial tilt for main Solar System bodies and major moons, over time. Is there an API availabe for this? I've checked JPL's Horizons API and ...
Eloy Villasclaras's user avatar
1 vote
1 answer
200 views

By how much does Haumea's fast rotation affect its surface gravity?

The equation for surface gravity is $\frac{GM}{r^2}$ but I'm not sure how to include the effects from its rotation.
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Does tidal locking also slowly reduce the orbiting body's axial angle?

The Moon is tidally locked to the Earth, and it has an axial angle of 6.687 degrees relative to its orbital plane. I'd like to know: did the Moon start out with a higher axial angle? In other words, ...
Humanist's user avatar
9 votes
2 answers
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Why is the sunset at different times at the same longitude at equinox?

I happen to live in two places that are literally at the same longitude but several thousand kilometers apart from each other (~47°N and ~68°N). It's just a few days until equinox - and I assumed that ...
Aileron79's user avatar
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1 answer
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Why both sunrise and sunset use the position of the sun's upper limb?

It is my understanding, that astronomical moments of both rise and set use the relative position of background object's upper limb to the foreground object's horizon. When were these definitions ...
user avatar
2 votes
0 answers
60 views

Do retrograde spin-orbit resonances exist?

The end state of rotation of an initially fast-spinning prograde terrestrial planet (in the absence of additional forcings such as "thermal tides" in an atmosphere, e.g. Venus) is a spin-...
user avatar
3 votes
1 answer
181 views

Kinetic energy and galaxy arm rotation rate

The higher than expected rotational velocity of stars and gas clouds in the outskirts of galaxies is explained today by invoking dark matter that supplies not only the additional gravitational mass ...
Keith Reynolds's user avatar
2 votes
0 answers
75 views

Has the computed change of the axial tilt ever been measured?

Earth, the 3rd planet from the Sun, sometimes faces earthquakes and seaquakes that are so strong that they reportedly change the axial tilt and/or the rotation velocity. These changes are merely ...
Ioannes's user avatar
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How can black holes spin if they're singularities? [duplicate]

How can black holes spin if the event horizon isn't a surface but just the border between where light can escape and where it can't? A black hole is assumed to be a singularity or the "entrance&...
Ioannes's user avatar
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3 votes
2 answers
496 views

As the Moon and the Earth are predicted to get into tidal lock, how slow would the Earth rotate?

This answer to Will the Earth ever be tidally locked to the Moon? supports the widely held thinking that during the Sun's red giant phase or later the Earth and the Moon should be tidally locked to ...
Ioannes's user avatar
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3 votes
2 answers
446 views

How to understand exactly why gravity darkening happens on rotating stars?

Phys.org's TESS delivers new insights into an ultrahot world links to KELT-9 b's Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment (readable in arXiv) The assymetric ...
uhoh's user avatar
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4 votes
1 answer
190 views

Isn't it absurdly unlikely that our Moon would constantly be "facing" us? [duplicate]

I never thought about this until recently, but our Moon is constantly rotating in such a way that it happens to perfectly be "looking at us" at all times. That sounds incredibly unlikely to ...
Bodhi Sinor's user avatar
5 votes
2 answers
3k views

How many times has the Milky Way rotated?

I would think that is a highly naive question, but I still ask it. Given current experimentally discovered numbers: the Milky Way galaxy is ~13-14 billion years old At the galactic radius where our ...
Mitch Harris's user avatar
0 votes
0 answers
30 views

Rotating observer plane inside celestial sphere with a given coordinates, time and date [duplicate]

I have plotted stars around the surface of a celestial sphere. At the centre of this sphere, I have a brown plane which is the land. This plane can be rotated in the x,y and z axis. When x,y,z ...
SidS's user avatar
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10 votes
1 answer
546 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
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1 vote
0 answers
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Lights moving fast and in a straight line coming from the northwest headed southeast tonight at 9:15CST [duplicate]

What is going on tonight? Bright lights in the same high orbit moving very fast across the night sky from Northwest heading southeast...then 10 minutes later same line but far fewer almost in ...
tom's user avatar
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1 vote
1 answer
406 views

Calculating the orientation of the night sky

How would one calculate the rotation/tilt of the earth to simulate the Night Sky in a self-written tool or app. I am trying to built an app for my telescope to show me on my phone what I am looking at....
PaddyDeveloper's user avatar
1 vote
0 answers
74 views

Why is rotational motion absolute, is the universe spinning? [duplicate]

When considering any object, one can say its translational movement is relative, depending on the point of view or reference frame adopted. If it moves at 1/4c relative to some observer, one might say ...
user avatar
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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3 votes
2 answers
1k views

Can you provide a visual description of the sun rise?

The Sun rises in the east only two times a year. The other days, the Sun rises in the east, but a little bit to the north, or to the south. How can you know the degree of how much north or south it is?...
user avatar
4 votes
1 answer
343 views

Definition of Rotation versus Revolution

Let there be a planet for which the duration of a solar day is equal to a year around the sun such that: ...
Aryaman Bansal's user avatar
2 votes
0 answers
31 views

Moon rotation tidal braking

Do we know if the moon had an initial rotation or did it coalesce tidally locked. If it had an initial rotation how long would it take to become tidally locked?
user36138's user avatar
  • 171
2 votes
1 answer
581 views

How can a star's rotation speed be measured?

How can a star's rotation speed be measured? If stars could be resolved, then you could use the Doppler shift to see that half of the star is bluer and the other half is redder, but stars (other ...
usernumber's user avatar
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2 votes
2 answers
283 views

When was the longest day on record?

The Earth's rotation is gradually slowing down. It was significantly shorter in the prehistoric past, but now we need to add a leap second every few years and we've not yet had to take any back. In ...
billpg's user avatar
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