Questions tagged [rotation]

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

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2
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1answer
45 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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1answer
94 views

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 ...
2
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1answer
68 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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0answers
33 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-...
2
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1answer
50 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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0answers
57 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 ...
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0answers
36 views

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&...
2
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1answer
99 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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2answers
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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
118 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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2answers
136 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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0answers
28 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 ...
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1answer
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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
77 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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I sighted a group of satélites moving in a interesting pattern in a way I never seen from this area where I live is this posible? [duplicate]

I live in the rural area of the state of São Paulo in brasil (mata atlántica). the sky is absolutely clear, when there is no clouds you see the milky way perfectly and a sky full of stars. I just ...
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1answer
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. ...
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2answers
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?...
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1answer
249 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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0answers
28 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?
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1answer
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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
138 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 ...
2
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1answer
71 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
101 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
67 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
36 views

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
109 views

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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0answers
25 views

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
82 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
155 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 ...
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1answer
140 views

Uranus' axis of rotation-when discovered?

Who discovered it, and how was that accomplished. I had assumed it was known before Voyager 2 arrived at the planet since it isn't mentioned in JPL voyager 2 Uranus Approach
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2answers
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Do we know of any tidally-locked planets with atmospheres?

If not, is there any reason such a planet couldn't exist? I ask only because that planet would literally have a twilight zone and I want to know that that's a thing somewhere.
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2answers
686 views

What would change if Venus rotated at a speed and direction similar to Earth?

I am interested in two aspects of this question. Imagine that Venus had a similar rotation speed and the same direction of rotation that we have here on Earth. What would change for Venus itself? I'm ...
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1answer
127 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 ...
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0answers
50 views

What maintains the high orbital eccentricity of many exo-planets near their sun?

Over the last decade we've discovered that many exoplanets not only have highly eccentric orbits, but also orbit very close to their sun. This is true of many classes of stars. I definitely have a ...
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1answer
87 views

Why doesn't the solar azimuth vary uniformly

For the past few dates, I've been observing the rotation of the earth around the sun and noticed that the azimuth of the sun doesn't vary uniformly throughout the day. The azimuth varies faster during ...
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1answer
83 views

Moon's revolution around the Earth and it's rotation around it's axis? [duplicate]

Does Moon rotate around itself while it makes one revolution around Earth or not?
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0answers
138 views

How to caclulate the chinese Three Gorges Dam impact on Earth rotation? [closed]

According to this January 2005 NASA JPL News item NASA Details Earthquake Effects on the Earth, the Three Gorges Dam has slowed down Earth's rotation by 0.06 microseconds per day. Having that weight ...
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1answer
3k views

Are these real paths of planets as traced from Earth?

Few days a go, I came across these two pictures of paths of planets as observed from Earth. They have a perfect geometric shapes. Actually, to me they look so beautiful and perfect, that they appear ...
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0answers
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How does a spinning black hole affect space-time compared to a non-spinning black hole?

I often see questions on this site that only apply to non-spinning black holes and often wonder how the answer would be different for a spinning black hole. As the title says, what are the major ...
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1answer
188 views

Why is Earth's rotation considered fast?

I'm currently reading Atom (Krauss book), and in chapter 11 there is this text: This collision can explain many things, including the high rate of spin of the Earth (the grazing collision would ...
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1answer
81 views

Are there known objects rotating at close-to-light speeds?

For example, $0.1c < v < c$? Is this actually possible? Background: is that true that the black hole in the center of the Milky Way rotates once per 20 minutes?
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1answer
56 views

The equation for calculating how many times Earth (or our solar system) has revolved around the Milky Way

I have seen it said on Quora and Reddit that it's about every 220-250 million years to go around the Milky Way from Earth. Wondering what the rough equation is for calculating it. That is, I guess, ...
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1answer
5k 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 ...
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4answers
4k 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.
2
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1answer
81 views

What causes random irregularities in the earth's rotation accounted for by dynamical time

I read in a book that the earth's rotation sometimes shows unpredictable irregularities(not caused by precession, nutation, tidal forces) which are accounted for using dynamical time. What would be ...
2
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1answer
80 views

Rendering asteroid orientation as seen from Earth

I am writing a program to render an asteroid as seen from various parts of the solar system. My goal is to roughly reproduce the image of Cacus according to information on its DAMIT detail page. ...