Questions tagged [rotation]

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

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1answer
164 views

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 ...
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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 ...
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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? ...
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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&...
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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 ...
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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 ...
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1answer
136 views

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?
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3answers
220 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 ...
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1answer
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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 ...
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1answer
128 views

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 ...
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1answer
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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 ...
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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 ...
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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 ...
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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 ...
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37 views

What should be the “poles” for irregular shaped bodies?

Continuation of: What is the definition of a "pole" of a celestial body? From uhoh's answer, we can conclude that a distinct bodies should have a center of mass. If the body is spherical, ...
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372 views

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 ...
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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 ...
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64 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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1answer
57 views

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, ...
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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 ...
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1answer
134 views

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 ...
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48 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-...
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52 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 mater that supplies not only the additional gravitational mass, ...
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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 ...
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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&...
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1answer
105 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 ...
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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 ...
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1answer
125 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 ...
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284 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 ...
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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 ...
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190 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 ...
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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 ...
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1answer
137 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....
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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 ...
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1answer
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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. ...
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2answers
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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?...
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1answer
272 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: ...
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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?
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1answer
79 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 ...
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2answers
149 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 ...
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2answers
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Which celestial body's length of day is closest to that of Earth?

I know the planets Mars and Eris are among bodies that have the most Earth-like mean solar days (about 24.67 and 25.9 hrs). Among moons there is Mimas of Saturn which has one of the most Earth-like ...
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1answer
101 views

How to calculate the true length of day on a celestial body?

When I only know the sidereal rotation period, how do I determine the true length of day on a body? We know the Earth's sidereal day doesn't have full 24 hrs unlike the true length of day. It's ...
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1answer
115 views

If Jupiter would stop rotating, would its atmosphere become homogeneous and single coloured?

Looking at pictures of Jupiter, there are many different colours and patterns. I imagine that the rotation has much to do with this, since there are horizontal "bands" across the planet along the ...
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1answer
165 views

How does the surface gravity on Mars vary between the equator and its poles?

A day on Mars is similar in length to the Earth's day. On Earth, due to rotation, the surface gravity varies from 9.78 m/s² (0.997 g) on the equator to 9.832 m/s² (1.003 g) on the poles. I wonder how ...
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1answer
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What are the smallest star clusters affected by Galaxy Rotation Curve?

We all know that Milky Way exhibits Galaxy Rotation Curve which makes it rotate very differently that Newtonian mechanics would expect. But Milky Way is a pretty large galaxy, and the one we only see ...
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4answers
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How are galactic rotation curves determined from radial velocity measurements?

I have been reading about the deviation of galactic rotation curves from the predicted Keplerian curve to a flat curve at large galactocentric distances. They were the first indicators of the ...
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Doppler Shift Vs Gravity Assist for Frequency Shifts from Rotating Galaxies

Frequency Shift of Light Leaving Rotating Galaxies: Differences in Doppler Shift due to Radial Velocity Vs Frequency Shift due to Gravity Assist from a Rotating Galaxy A description of estimating ...
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1answer
113 views

How to convert from FELO-HEL to Km/s?

I am using DS9 to calculate the rotational velocity of a galaxy. I have 21cm cube and I used DS9 to plot this graph I do not understand what is FELO-HEL! and I want to convert the units from FELO-...
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1answer
181 views

What is a black hole's “shadow” and the best angle to view it to measure the spin?

This excellent answer mentions several ways to try to observationally measure the spin of a rotating black hole. The third one is intriguing, but I don't understand how this works: The spin of a ...
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Why does the outside edge of a Kerr black hole ergosphere rotate at the same speed as the inner edge?

Reading through the Wikipedia on a Kerr black hole ergosphere, and this nice question on the maximal spin rate of a black hole leads me to ask: why does the outer edge of the ergosphere rotate at the ...