Astronomy Stack Exchange
Astronomy Stack Exchange

Questions tagged [rotation]

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

247 questions
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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 would be very strange if they didn't. They couldn't…
Deschele Schilder
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Do solstices and equinoxes shift over time?

Right now, I think the winter solstice is around December 21. Has it always been around this date constantly? Since the earth's axis's 23.45° tilt will be on the exact opposite side in 13000 years (or was 13000 years ago) due to precession, it'd…
Mickael Caruso
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Identify Greek letters used in formulas

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 characters, so it's hard to tell.
posfan12
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Is there any difference between rotation axis 90 degrees and 270 degrees?

Is there meaningful reason to distinguish 90 and 270 degree rotational axis?
Gstestso
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Reference point for the directions

Are directions [North, South, West, East] derived from Earth's rotation around its axis? What makes north north and the south south? Is it arbitrary or is there some specific reference point?
Bill Thompson
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Axial Tilt One or Two Angles

Why is the axial tilt of a planet expressed as a single angle when two angles are necessary to specify a point on a sphere? Imagine if the Earth’s axial tilt were 90 degrees, then the axis of rotation could point anywhere along the circle in the…
tomek dobrzynski
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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 CSPICE toolkit, but as far as I've seen axial tilt…
Eloy Villasclaras
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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 too, and the cycle of the earth making a full…
Lance
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Are harmonic relationships among the rotation periods of the planets well known? Are they factors in other planetary phenomena?

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 min. Note the similar relationships with the…
user23167
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What makes a flying object keep moving with the Earth's rotation?

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?
Muhammad Usman Qureshi
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How would seasons at the equator be if the Earth were tilted 90 degrees?

If Earth's axis of rotation were tilted 90 degrees, what type of seasons would be observed at the equator. My prediction is that there would be no seasons, as the orientation of the equator would be the same as if the Earth
John Michaels
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