Questions tagged [celestial-mechanics]
Questions regarding the motions of celestial objects.
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Planetary Declination and Axial Tilt
Is it a coincidence that Earth's axial tilt and maximum declination are both approximately 23 degrees?
Mechanically speaking, do planets physically cross the Solar equator, or is declination due to ...
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0answers
30 views
Eccentricity from Analemma
Can the eccentricity of a planet's orbit be found just from the analemma of its star? We can draw an analemma given the axial tilt and eccentricity, but how do we find the reverse?
Note: I already ...
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54 views
Undisturbed planetary alignment after galactic collision
How do planets still orbit around the empty space where a black hole was after a black hole absorbs the milky way's black hole and keeps moving through space without disturbing surrounding planets ...
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1answer
93 views
Determine Julian Date from Gregorian without formula
As an exercise, I am trying to calculate the JD from a given date in the Gregorian Calendar at a time given in UT. Furthermore, I want to do so from first principles without relying on any formula. ...
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1answer
70 views
How was Cruithne's orbital time calculated?
How was it determined that Cruithne takes 770 years to complete its cycle with Earth? Janus and Epimetheus were disovered long enough ago, and have short enough cycle times, that we've had time to ...
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2answers
134 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 ...
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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 ?
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1answer
204 views
Why is Uranus able to support a regular satellite system?
Uranus has an obliquity of 98° which means that the mutual inclination between a satellite orbiting in its equatorial plane and the orbit of Uranus around the Sun would exceed the critical angle for ...
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49 views
Expansion of Jupiter's perturbing effects on Kepler's third law treatment of orbits?
Does anyone know any good reference for how this was done?
I remember reading once about how Jupiter's gravitation can be treated as a perturbation, but I cannot find it again now. I think they ...
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1answer
88 views
What does “all stop” mean in reality?
In science fiction, when a starship captain commands "all stop," the audience simply assumes that, like a terrestrial naval ship anchored to the ocean floor, the ship literally comes to a complete ...
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2answers
282 views
How does the Sun orbit the Sun-Jupiter Barycenter?
I got the Orbital Elements of Jupiter around the Sun, which describe how it orbits relative to the "fix" Sun.
Jupiter
Semi Major Axis (AU): 5.20336301
Eccentricity: 0.04839266
Inclination to ...
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1answer
70 views
Why does the precession of the earth affect other planets?
In the Wikipedia article on numerical integration of planetary motion it states:
...the flattening of the Earth causes precession, which causes the
axial tilt to change, which affects the long-...
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98 views
Is the Milankovitch calendar provably better than the Gregorian one considering a non-constant tropical year?
It's somewhat of a no-brainer the revised Julian calendar (attibuted to Milankovitch) is more accurate than the Gregorian one just because it started with a more accurate estimate of the duration of ...
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117 views
Why planets and stars are always round/oval in size? [duplicate]
What kind of stability it provides to each and every celestial body that each one them are round in shape?
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1answer
181 views
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 ...
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1answer
187 views
How to compute the perihelion precession of Earth's orbit?
I want to simulate the perihelion precession of Earth. I tried searching other posts in stack exchange as well relating this question but may be it's my fault that I couldn't understand their answers....
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174 views
Can Two Stars of One Same Type Orbit Each Other?
This is a simple, textbook definition of a binary star orbit. One low-mass star orbits a higher-mass star in a narrow but definitive center. For example, the high-mass star would be our own sun--a G-...
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178 views
How can Earth-Sun Lagrange points L1 & L2 even be semi stable considering the moon?
I know that the Earth-Sun Lagrange L1, L2, and L3 points are not considered stable over longer periods, especially when compared to L4 and L5... But, with the moon orbiting the Earth in the general ...
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1answer
57 views
Calculate NEO object position with nasa Near Earth Object data
I wish to create a 3D visualisation of NEO's by date in relation to earth, but calculating their position at that time has got me stuck.
From this question I was able to fine Nasa's NEO object data:
...
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412 views
Equations of motion for Earth and Moon
One of the simplest versions of Newton's equations of motion for the Sun, Earth and Moon can be obtained by making the approximation that the three bodies are perfect spheres. In this approximation, ...
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1answer
168 views
Is it true that open clusters have $E > 0$ and globular clusters have $E < 0$?
I just need to confirm or refute something I'm believing since a very long time, maybe without real evidence.
Can we distinguish stellar clusters by their total mechanical energy ?
Is it true that ...
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2answers
175 views
Celestial navigation from scratch
Is it possible to establish one's longitude and latitude by observing the stars? Can you use observations of the stars to find the relative distance between two locations, which would be useful in map-...
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118 views
Angles in Moon, Earth and Sun system
Consider the vector positions of the center of mass of Moon, Sun and Earth, $\vec{r}_{\rm M}$, $\vec{r}_{\rm S}$, $\vec{r}_{\rm E}$, respectively, in a given reference frame.
Consider:
the angle ...
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1answer
421 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....
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1answer
122 views
Sky in the very far future / past
Motivated by this question about a stranded submarine in the Jurassic I would like to know:
Is there anything remotely left of our current skyline if we go back or forward millions of years so that ...
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2answers
2k views
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 ...
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1answer
299 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-...
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Is there any way for a planet orbiting a red dwarf in the habitable zone to not be tidally locked?
Is there any way to avoid the tidal locking of a planet orbiting a red dwarf in the habitable zone?
For example, could a planet with a 90° obliquity and large moon avoid such a situation?
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1answer
620 views
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)^{...
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1answer
126 views
On orbital mechanics of evaporating planets
A planet orbits around its sun on an elliptic orbit, and loses mass slowly due to evaporation. How will the parameters of the orbital ellipse change as a function of time?
Could we do a generalisation ...
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3answers
382 views
Creating a basic “fixed” solar system to host a 3D space travel simulation
I'm trying to simulate a virtual/imaginary "solar system" in software--just a hobby project for now. Unfortunately this has made me realize exactly how much math I've forgotten since college.
...
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0answers
131 views
The path of the planets on the celestial sphere
I know that planets have a "wandering" movement on the celestial sphere. I also know that their period around the Sun vary largely as compared with the period of the Earth (one sidereal year), ...
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3answers
584 views
Question about the Figure-eight periodic planar three-body motion
If this is a posible periodic solution for a three-body problem, can anybody tell me where is the center of mass of the system? As we know, in a n-body problem the bodies orbit around their center of ...
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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, ...
9
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2answers
570 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 ...
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1answer
383 views
Two body orbit of equal masses
Given two bodies of equal mass in an elliptical orbit:
I know they will be orbiting about a common center of mass, i.e. the barycenter. But, do the velocities have to be equal in magnitude and ...
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2answers
146 views
Is the motion of the Sun around the Galaxy a result of gravitational pull?
Does the orbit of the sun (and other stars within the Milky way) around the galaxy result directly from radial gravitational force toward the objects in the center of the galaxy, or is there ...
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1answer
43 views
Has celestial navigation been materially impacted by the imperfect nature of celestial reference frames over time?
In this video on inertial reference frames, it is mentioned that the stars are humanity's best inertial reference frame: the earth experiences a subtle acceleration relative to the sun due to the ...
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1answer
57 views
Why is it so difficult to discover the earth Trojan?
It is discovered only in 2011.
Why is it so late?
We know where to find it.
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1answer
267 views
In a binary star system, what relation determines the eccentricity of the three orbits (for $m_1$, $m_2$, and the reduced mass)?
In a binary star system, why does $$e_1 = e_2 = e$$
where $e_1$,$e_2$, and $e$ are the eccentricities of the three orbits of $m_1$,$m_2$, and the reduced mass, respectively.
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288 views
Why don't the stars in a binary star system of equal masses always orbit their center of mass in a circular orbit?
If I have a binary object system of equal masses, why don't they always have the same circular orbit around their center of mass, like in the photo?
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1answer
147 views
Do orbital resonances always form naturally?
For example, if I throw two planets to orbit a star at random direction, would they form an orbital resonance?
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595 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, ...
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2answers
267 views
How do rogue planets orbit around stars in other planetary systems?
I got some interesting answers for What would happen if a rogue planet hit one of the planets in our Solar System?
But I have seen some documentaries that state that rogue planets from other ...
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1answer
3k 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, ...
4
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1answer
180 views
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 ...
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1answer
526 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 ...
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501 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 ...
