Questions tagged [celestial-mechanics]

Questions regarding the motions of celestial objects.

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Need Simple equation for Rise, Transit, and Set time

I've been looking, unsuccessfully, for hours for a simple set of equations: Input: RA and Dec of an object Observers Lat and Lng Current Time Output: Rise Time Transit Time Set Time (and, ...
W. Christopher Moses's user avatar
36 votes
1 answer
12k views

Why do the planets in our solar system orbit in the same plane?

(Yes I'm excluding Pluto from this the same way it was excluded for not being a planet) Observing the planets orbit of the Sun they all seem relatively planar and roughly all orbit along the same ...
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39 votes
3 answers
20k views

Is Venus in some way tidally locked to... Earth?

The video here demonstrates how Earth sees the same face of Venus every inferior conjunction (i.e., two planets are the closest to each other): https://www.youtube.com/watch?v=4m_ouMC61-w (or https://...
puzzlet's user avatar
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27 votes
2 answers
9k views

Where do we have it from that the Moon is migrating away from Earth?

I know Neil Armstrong placed a mirror on the Moon and people shoot lasers there which get reflected, thus measuring the time the light needs they can conclude the current distance of the Moon. But the ...
Ioannes's user avatar
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11 votes
2 answers
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The deduction of the Hill Sphere formula

This question may be a little lazy, but can anybody give me a proof of the Hill sphere formula? Acording to wikipedia, the formula for the radius, $r$, is $$r\approx a(1-e)\left(\frac{m}{3M}\right)^{...
Carlos Vázquez Monzón's user avatar
6 votes
1 answer
5k views

What causes objects to become tidally locked?

I'm trying to write a gravity simulation (suns planets etc), and was hoping tidal locking could be one feature demonstrated. Using a simple equation for gravity has produced some interesting results, ...
Ninjanoel's user avatar
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9 votes
2 answers
780 views

Is Io's orbit or rotation affected by its volcanism?

The rotations of comets and asteroids are affected by outgassing volatilities. Io is very volcanically active. Does this give Io a varying orbit and a slow rotation? Tidal forces should take longer ...
LocalFluff's user avatar
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8 votes
3 answers
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Implementation of formulae for Meeus for the Moon

With Astronomical Algorithms by J. Meeus (1998) I have obtained the relevant illuminated fraction of the disk and position angle. But they're numbers (all Greek to me!) I know, Meeus explains that ...
Danny F's user avatar
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6 votes
3 answers
1k views

Open source code for the maths behind a heliostat?

Theoretically, using a Raspberry Pi, (at least) one mirror, and two motors, one should be able to build a heliostat, i.e. a device which redirects sunlight to a fixed spot, like a scrub in the shadow ...
B--rian's user avatar
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5 votes
1 answer
257 views

Explanation about the resonance, mean motion resonance and libration

I am studying for a project the dynamics of multi-planetary system in resonance. I have two questions about this domain. In many articles they speak about 'mean motion resonance', what is the ...
Adrien Chimay's user avatar
3 votes
1 answer
618 views

How can the next supermoon be analytically predicted?

The lunar motion can be predicted with basic celestial mechanics, but the perigee and apogee are not always the same, basically because the attraction of the Sun makes some oscilations in the semi-...
Carlos Vázquez Monzón's user avatar
2 votes
1 answer
126 views

What is the difference between SPICE kernels and JPL Development Ephemerides? Is a DE just a bunch of kernels on a string?

My imposter syndrome is acting up again after I posted several comments under: What is the mathematics needed for understanding DE440 and translating it into xyz coordinates? Now I feel like I don't ...
uhoh's user avatar
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1 vote
3 answers
2k views

Why does east and west appear to be mirrored in the celestial sphere?

I'm wondering why East is left and West on the right of the celestial sphere if you look at images of it? Example below: (source)
Benjamin's user avatar
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9 votes
1 answer
358 views

If Saturn's rings cannot coalesce into a moon because of tidal forces, then how are shepherd moons able to exist?

From Wikipedia: In celestial mechanics, the Roche limit, also called Roche radius, is the distance within which a celestial body, held together only by its own force of gravity, will disintegrate due ...
user177107's user avatar
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9 votes
2 answers
1k views

clarification of the Kozai mechanism

As Wikipedia says, In celestial mechanics, the Kozai mechanism, or the Lidov–Kozai mechanism, is a perturbation of the orbit of a satellite by the gravity of another body orbiting farther out, ...
questionhang's user avatar
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8 votes
2 answers
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Is Pluto a "proto-planet"?

My question is this : could the Charon-Pluto system becomes in the coming few millions years a full fledged planet, as in the IAU classification ? I ask this because there are two facts that bother ...
Cqoicebordel's user avatar
7 votes
1 answer
799 views

Could an ejected "extra ice-giant" still be lurking in distant solar orbit?

BACKGROUND Hot Jupiters are thought to have migrated inwards, implying that another giant planet has been ejected in order to conserve the orbital momentum of those planetary systems. The number of ...
LocalFluff's user avatar
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6 votes
2 answers
866 views

Has any moon achieved "retrograde equatorial orbit"?

There are many moons which have low (almost negligible) inclination and can be considered to rotate at the planet's equatorial plane. For instance, Galilean moons have almost negligible inclination (&...
Nilay Ghosh's user avatar
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5 votes
2 answers
595 views

What variables are needed to calculate simple horseshoe orbit times?

EDIT This was NOT a duplicate of Horseshoe orbit cycle times. But that other question has been deleted, regardless. My original question asked for the answer to the equation(s), and provides many of ...
Harthag's user avatar
  • 379
4 votes
1 answer
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Determining North-South Line Via Watch Method: Theory & Reason

I recently read that if you're in the northern hemisphere and have an analog watch, then you can point the hour hand at the sun and know that a south line lies between (bisection) the hour hand and ...
user8110's user avatar
4 votes
1 answer
1k views

Do all the planets travel along the same constellations?

If humans ever moved to another planet in this solar-system, what constellations would the sun meet from that perspective? What constellations would the sun look like it is meeting from the ...
Atlas's user avatar
  • 67
4 votes
2 answers
547 views

How is Earth's Rotation Angle (ERA) defined and measured

UTC typically ticks with TAI. But to keep UTC from drifting far from the rotation angle of the Earth we occasionally add leap seconds to ensure that UTC does not drift too far from the UT1 timescale. ...
Jagerber48's user avatar
3 votes
1 answer
750 views

Requirements for a satellite/planet to be tidally locked to a planet/star

The Moon is tidally locked to the Earth, the Four Galilean are tidally locked as well, and the recently found planetary sistem TRAPPIST-1 has seven tidally locked planets, but Venus or Mercury are not....
Carlos Vázquez Monzón's user avatar
3 votes
3 answers
2k views

Why does the Sun track out a seemingly sinusoidal path on the celestial sphere?

The question arose because I wanted to understand the path of the ecliptic after reading about it here: https://johnlucey.webspace.durham.ac.uk/users/solar-year/ Is the sinusoidal path due to Earth’s ...
keynes's user avatar
  • 31
3 votes
1 answer
1k views

Roll, Pitch and Yaw of Orbital Planes

I have been reading about celestial mechanics and particularly about planetary orbits. I understand that a planet's orbit can be tilted (pitched) with respect to the Earth's ecliptic and that it might ...
Spencer Rugaber's user avatar
3 votes
2 answers
150 views

Can we learn anything from the chaotic movement of Hydra and Nix?

The NASA Visualization Explorer Moons In Chaos says Hydra and Nix, two of the moons of Pluto, show chaotic movement due to the shifting gravitational field. How long a day lasts and where the sun ...
Bahnhofstrasse's user avatar
2 votes
2 answers
777 views

How can the Earth and the Moon be in synchronous rotation if the Moon won't be in geostationary orbit?

It is said that the Moon moves away from Earth and that during the Sun's red giant or white dwarf phase the Moon will be about 40% farther than now and in a synchronous rotation ("hantle rotation&...
Ioannes's user avatar
  • 1,090
2 votes
1 answer
170 views

What is the mathematics needed for understanding DE440 and translating it into xyz coordinates?

I would like to write my own code to process NASA's DE440/DE441 ephemerides, but I do not know the mathematics needed to do this. I understand packages such as pyephem have implemented variations of ...
Ana's user avatar
  • 181
2 votes
1 answer
118 views

Hierarchy of gravitational interactions of astronomical objects: from single to large-scale structures

Hierarchical structure is clearly visible in the Universe. The "observable universe" includes almost empty voids, between which lie large cosmic filaments. The filaments consist of galactic ...
dtn's user avatar
  • 706
1 vote
1 answer
111 views

Does the Honey moon have a precession problem?

In Steven Colbert's interview with Neil deGrasse Tyson after about 03:16 the following is explained: But wait, all the moons - all the full moons of the year have ...
uhoh's user avatar
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1 vote
1 answer
392 views

Keplerian Elements

So, I've been doing endless research, and I've found a bit of information, all in different places, that is. Now, I'm getting really confused about it; I can't keep up with it all anymore, so, now, it'...
Questioner's user avatar
-3 votes
2 answers
373 views

What pulls the Sun above the galactic plane and pulls it below the galactic plane?

Since the sun climbs above the galactic plane and it even dives below the galactic plane we can't deny that it wouldn't climb upward unless there is something above the galactic plane that pulls it ...
S C Sawhney's user avatar