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Questions tagged [rotation]

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

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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 -- ...
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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 ...
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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 ...
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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 ...
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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 ...
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How does motorized ALT-AZ mount work? [duplicate]

I can easily understand how an equatorial mount can cancel earth rotation by aligning the RA axis on the earth rotation axis. The RA axis can be motorized at constant speed, doing a full revolution ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Why Euler's rotation theorem doesn't govern (or still governs) gas planets such as the sun?

As stated and discussed in Physics SE: Euler's rotation theorem guarantees that any rotation of a rigid object can be expressed as a rotation around a single axis. Or, Angular rotation is a ...
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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 ...
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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 ...
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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 ...
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1answer
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Do the number of moons a planet has affect the speed of the planet's rotation?

Would the tidal forces of multiple moons interacting upon a planet speed up or slow down the day length of the planet? I was thinking that maybe the planet's day length would be slowed down due to all ...
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How can I calculate how far through the day the prime meridian is of different planets

I'm trying to create a widget that shows the 'time' on different planets. It will show how far through the day/night cycle (as a percentage) a point on the planet is. It has been easy to scale down ...
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If the Earth is rotating counter clockwise, how does the sun rise from east?

I was very confused when I watched this video from 2:18 till 2:45. And it seems very clear that if the Earth is really rotating from west to east, shouldn't be the Sun rising from west and setting in ...
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IAU rotation model

I'm looking at this IAU WGCCRE Report: http://aa.usno.navy.mil/publications/reports/Archinaletal2011a.pdf It gives expressions for Earth orientation relative to the International Celestial Reference ...
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Why most planets don't spin retrograde? [duplicate]

Edit: just found duplicate Since orbital velocity is greater on small orbits, and smaller on large orbits, why don't planets spin retrograde around their own axis? One portion of planet's mass is ...
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Any method to apply inverse TPoint model?

I have an automated telescope that I have written some software for. I am currently using TPoint to compensate for some of the irregularities of my system. However with TPoint you apply an offset (...
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2answers
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Circular velocity in axisymmetrici potential [duplicate]

If a matter distribution is spherically symmetric, the circular velocity is straightforwardly related to the mass via: $v_{circ} = \sqrt{GM/r}$ In an axisymmetric potential, on the other hand hand, ...
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What contributes the most to the seasonal temperature variation?

The seasonal temperature is ultimately due to the precession of the Earth around the axis. But what I'm curious about is... is it due more to the side experiencing winter being farther from the sun ...
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Shapes of orbits of celestial bodies [duplicate]

Why are the shapes of almost all celestial bodies (not only planets of Solar System) are elliptical in nature rather than circular ? Is it because of more stability that rotating objects get when ...
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1answer
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What are evidences of stationarity of rotation of galaxies

Recently I have found the article Does There Really Exist the Problem of the Dark Matter in Spiral Galaxies? which states that dark matter does not exist because astronomers are wrong assuming ...
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Earth shape and rotation

Imagine a helicopter that took off from point A and goes vertically in the air to a certain fixed point B in the atmospheric area at a certain fixed altitude with enough fuel to stay there (at point ...
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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? ...
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Calculating Orientation of Planet in J2000 Heliocentric Ecliptic Coordinates

I'm trying to calculate the orientation of celestial objects at any given time. The end goal is e.g. a quaternion that transforms a planet, with axis perpendicular to the ecliptic and oriented so $0^\...
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Is the Sun prograde or retrograde with respect to the rotation of the Milky Way?

I recently learned about the terms prograde and retrograde. I've seen these terms used to describe the rotations and orbits of moons with respect to their planet, and planets with respect to their ...
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Does the Abell 1689 supercluster have angular momentum?

The Abell 1689 is a large group of galaxies, containing a lot of elliptical galaxies : https://en.wikipedia.org/wiki/Abell_1689 Usually, an elliptical galaxy don't have large angular momentum around ...
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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?
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rotation curve in the innermost part of galaxies

I read in Sofue's articles (1999) that he used a method to investigate the bulge of galaxies to obtain rotation curve of this part of galaxies. So my question is how could Vera Rubin et al. obtained ...
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Are exoplanets at dwarf stars less likely to have super-rotating atmospheres or asynchronous tidal locking?

Dwarf stars have terrestrial sized planets orbiting in habitable zones very close to them. These exoplanets are often said to be tidally locked to their star, like the Moon is to Earth, and that they ...
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Calculating length of summer solstice day using tilt and latitude

I want to be able to predict how long the summer solstice lasts at any part of world given the maximum tilt angle $φ = 0.4101524 \; \mathrm{rad}$ and the latitude $θ \; \mathrm{rad}$. I specifically ...
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1answer
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Assuming 2007 OR10 is in tidal lock with its satellite, what is its mass?

Its rotation period is 45 hours. Its satellite is at the distance of 15000 km. Given this data, and assuming the satellite's orbital period the same as the main body's rotation period, 45 hours, what ...
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Day/Night Cycles and Seasons if the Earth's Rotational Axis and Orbit Changed

I just enrolled in an introductory Astronomy course, and today in lecture the professor asked this question: Give 4 ways in which the day/night cycle and the seasons would behave on Earth if our ...
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Why do Uranus' and Pluto's moons orbit the equator? What makes a moons' inclination tilt with the rotational axis of their planet?

Uranus and Pluto have their axes of rotation almost 90 degrees towards the ecliptic. But why do their moons tilt the same way? Does it mean that their tilts were caused by passing near some external ...
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Which celestial object in the solar system has the fastest tangential velocity at its surface?

Consider all of the naturally-occurring objects in the solar system : in the reference frame of the object's center (ie, ignoring the orbital velocity around the sun or, in the case of satellites, ...
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Is it true dark matter was discovered whilst looking at the rotational speed of galaxies?

Just a little something whilst a dark matter pioneer moves onto a better place. This commentator writes: My understanding is that dark matter was "discovered" when trying to find out why stars in ...
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How does the dense atmosphere of Venus affect the planet's rotation?

Reading through questions about my favourite planet, Venus, I came across this answer to the question What is the current accepted theory as to why Venus has a slow retrograde rotation?, specifically ...
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Precipitation and weather and seasons on other planets [closed]

I have participated in an exhibition on astronomy and decided to make a project on the topic "weather season and precipitation on other planets" I have the knowledge about the weather on earth but I ...
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The drift of the Moon's equatorial rotation velocity

Are there any citation or documentation showing the measured degradation of the Moon's equatorial rotation velocity (thus affecting its moon's axial rotation)? I am looking for the drift of the Moon'...
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What makes a flying object keep moving with the Earth's rotation? [closed]

When a bird is flying or when a copter is hovering or a plane is flying what force is making them rotate with the earth beneath them?
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What makes the Earth infinitely rotating around its axis

I was reading two sites before I posted the question here. One site says something like that the collisions in Universe eventually set the planets rotating, another site says that our planet is formed ...
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Are there any known planets whose axis is oriented such that one pole always faces its star?

Earth rotates around the sun and around its axis (A North, South axis) giving us days, nights and seasons. Are there any known planets that rotate with an axis pointing toward its sun so that one ...
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Could the merger of two rotating black holes create another that breaks the rotational speed limit?

The black hole GRS 1915+105 was observed to be spinning at near the theoretical maximum spin rate. Assuming you had two such black holes spinning clockwise, and also orbiting each other clockwise, ...
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How is a day measured on a gas giant?

After watching this JPL video of a Cassini time lapse of Saturn, I wondered since being mostly gases, how do we know how long a day—one rotation period—is? Is there a usable relation between how fast ...
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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 ...
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How to get the axial tilt vector(x,y,z) relative to ecliptic

According to the orbital plane XYZ, I understand that the axial tilt is the angle between the planet axis rotation and any normal of the plane (actually Z in right handed system). BUT, this is not ...
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Why do our clocks not go out of sync with the day over a year?

Ok, so our clocks time 24 hours, 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 '...