Questions tagged [rotation]
Questions regarding the action of or an object rotating along an axis.
143
questions
2
votes
1answer
42 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 ...
3
votes
1answer
87 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 ...
1
vote
1answer
49 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 ...
1
vote
1answer
33 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 ...
2
votes
4answers
64 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 ...
1
vote
0answers
23 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 ...
2
votes
1answer
59 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-...
4
votes
1answer
119 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 ...
3
votes
0answers
43 views
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 ...
3
votes
1answer
119 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
2
votes
2answers
77 views
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.
2
votes
2answers
220 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 ...
1
vote
1answer
103 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 ...
1
vote
0answers
40 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 ...
2
votes
1answer
65 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 ...
1
vote
1answer
71 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?
2
votes
0answers
87 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 ...
2
votes
1answer
1k 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 ...
1
vote
0answers
115 views
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 ...
5
votes
1answer
186 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 ...
3
votes
1answer
79 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?
1
vote
1answer
51 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, ...
41
votes
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 ...
17
votes
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
votes
1answer
65 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
votes
1answer
69 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.
...
10
votes
2answers
101 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 ...
3
votes
1answer
137 views
Is it possible for stars not to rotate?
I'm just curious about that the existence of non-rotating stars. Is it physically possible for a star not to rotate at all? Does magnetic braking eventually stop the stellar rotation?
0
votes
1answer
82 views
Will Earth at some point stop rotating anti-clockwise, stay still, and then rotate clockwise? [duplicate]
Will Earth at some point stop rotating anti-clockwise, stay still, and then rotate clockwise?
1
vote
0answers
60 views
If Earth suddenly stops rotating, will be thrown at 465 m/s? [duplicate]
If Earth suddenly stops rotating, will be thrown at 465 m/s ?
9
votes
1answer
79 views
How a star's rotation affects a star in the main sequence?
I searched and have found that the questions mainly focus on neutron stars, white dwarves and black holes. This was not what I looked for.
Basically, the bigger the star's mass is, the more intense ...
1
vote
2answers
87 views
What is meant by sun's path through zodiac
I read somewhere that sun's daily course and complete cycle is visible in the ecliptic belt by zodiac constellations.
I didn't understand what that means closest I could find online is: https://www....
-1
votes
1answer
244 views
Why is the shape of the Moon spherical? [duplicate]
The Moon does not rotate on its own axis. If I am right, for something to gain a spherical shape it has to rotate on its own axis. We know that the Moon does not rotate on its own axis. How can this ...
17
votes
3answers
5k 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 ...
1
vote
1answer
76 views
Cycles that are longer than the year, but less than 1000 years
Wondering what primary astronomical cycles there are that are greater than a year (which is a cycle around the sun), but less than 1000 years-ish (on that scale). There is the cycle of the moon phases ...
3
votes
2answers
149 views
If a giant object would approach the Earth, would Earth start to turn faster or slower while the object starts to become nearer and nearer?
I am asking myself this question: if a giant celestial object would approach the Earth, would Earth start to turn faster (then day duration would be diminished) or slower (day duration increased) ...
12
votes
3answers
177 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?
8
votes
1answer
685 views
Can one detect from earth that angular momenta of its axial rotation and its orbital rotation are “almost parallel”?
I mean that the angle between these angular momenta is acute as opposed to obtuse (23.5 and not 180-23.5), so that the rotations are "roughly in the same direction".
Related but distinct question -- ...
3
votes
2answers
98 views
Can a planet's changing tilt be aligned with the rotation around its star? [duplicate]
What I'm asking is if the tilt of a planet can "follow" the rotation around its star so that, for example, its north pole would always lean towards the star, and thus always be under daylight. The ...
2
votes
1answer
125 views
Identify Greek letters used in formulas [closed]
Could anyone tell me what the names of the Greek letters in the screenshot are? Is the first one alpha? They are used in calculating ICRF rotations. Wikipedia uses a different font for their list of ...
2
votes
0answers
131 views
Modeling planet rotations (time of day, obliqueness, etc.)
I created this solar system model using POV-Ray:
by following these instructions:
https://ssd.jpl.nasa.gov/txt/aprx_pos_planets.pdf
The next thing I want to do is orient/rotate each globe correctly ...
8
votes
1answer
373 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 ...
2
votes
1answer
123 views
Is it possible to define a state of zero absolute angular momentum anywhere in the universe?
Conservation of angular momentum doesn't seem correct to me. I think this because radiation is present everywhere, no space is completely void, and no object perfect. Thus all objects will have uneven ...
2
votes
1answer
34 views
Relationship between galactic rotation and stellar lifetime
I have read that the lifetime of stars is much less than the period of rotation for a spiral galaxy. For example https://www.coursera.org/learn/evolvinguniverse/lecture/wlYhz/the-origin-of-spiral-arms ...
1
vote
2answers
100 views
Are harmonic relationships among the rotation periods of the planets well known? Are they factors in other planetary phenomena? [closed]
Every 39.88 minutes 10 degrees ($\frac{360^\circ}{36}$) of arc passes over the zenith. It can also be stated that the 36th harmonic of the rotation period of the earth (1435.8 min) is equal to 39.88 ...
2
votes
1answer
128 views
Which direction do the constellation revolve in?
If I am standing looking towards the East from the Northern Hemisphere, do the constellations appear to rotate towards the West via the North or the West via the South or am I completely off target ...
5
votes
1answer
132 views
How can a rotation period of a planet's satellite/moon be “chaotic” (like Hyperion around Saturn)?
According to wikipedia (see info below image) Hyperion's rotation period around Saturn is "chaotic".
What does that mean? The period (in days/hours) is different every rotation without any law ...
-4
votes
2answers
338 views
Why isn't the Sun hollow? [closed]
[Edited to remove incorrect geological assumptions]
The sun is self-rotating, i.e. it spins on its axis. When something spins, there's an apparent force away from the centre, and matter gets flung ...
3
votes
3answers
422 views
angle to the equator of the Sun on sky at a given time
Is there an easy way to tell at what angle the solar equator is wrt the horizon at any given time of the day? I would think that it rotates 180 degrees from sunrise to sunset, but not in a linear ...
3
votes
2answers
910 views
Does Polaris have a trail in the sky timelapse?
I came across few sources that claim Polaris movement cannot be observed with the naked eye. But then, I saw images of the star trails (timelapse), and they clearly show Polaris not quite at the true ...
