33
votes
Accepted
Is it possible to have a stable 3 body system that orbits in a perfect circle?
Yes and No. — It depends on what you mean by "stable". To be precise, "stable" means immune to small perturbations. "Equilibrium" can be either "stable" or &...
- 115k
18
votes
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Why do people choose 0.2 as the value of linking length in the friends-of-friends algorithm?
The friends-of-friends (FOF) algorithm (Huchra & Geller 1982; Press & Davis 1982, Davis et al. 1985) for finding groups of particles can be used for various numerical problems, not just ...
- 37k
16
votes
Does the barycenter of an n-body system remain constant during collisions?
Conservation of momentum dictates that if there are no forces external to the system then the barycentre will not be accelerated.
That means the second derivative of its position with respect to time ...
- 146k
15
votes
Accepted
What is Gravitational softening length?
Gravitational softening is a numerical trick introduced in particle simulations to avoid too close encounters that would otherwise result in unrealistic motion of particles.
The gravitational force ...
- 37k
13
votes
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Is Universe Sandbox 2 realistic?
Not sure if these kinds of questions are allowed here, but I may as well answer it.
Universe Sandbox 2 is mostly realistic. Its accuracy degrades as you increase the flow of time. The slower the time,...
- 8,098
13
votes
Accepted
N-body simulation still losing precision despite using arbitrary-precision arithmetic and symplectic integrator
There are various possible causes for an orbit simulator to behave poorly, even when using an excellent arbitrary precision package like mpmath. When supplying numerical values, you need to pass them ...
- 13.1k
12
votes
Accepted
How to discover Neptune from the Uranus orbit (by computer simulation)
Here is what I did:
Based on their masses, it is safest to initially consider Jupiter and Saturn as well as Uranus. It might also be fruitful to include the Earth in the analysis, to get relative ...
- 421
10
votes
Would it be possible for a planet to orbit around a trinary star system in a figure 8 orbit?
There are periodic orbits, but "stablity" is more doubtful. In fact there are thousands of these. See https://numericaltank.sjtu.edu.cn/three-body/three-body-unequal-mass-movies.htm. For ...
- 115k
9
votes
Would it be possible for a planet to orbit around a trinary star system in a figure 8 orbit?
It is perfectly possible for a planet to have a stable orbit around a single star. There are many examples in our own solar system and in other star systems.
It is perfectly possible for a planet to ...
- 7,411
8
votes
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More recent data and simulations of "Milkomeda", the collision of the Milky Way and Andromeda galaxies?
Since the second data release (DR2) of the European Space Agency's Gaia mission there has been a revolution in astrometry, including measuring the motion of the Andromeda Galaxy.
On February this ...
- 3,856
7
votes
Accepted
If an orbit is shifting due to orbital precession, is it still a Keplerian orbit?
No orbits are strictly Keplerian, unless you really monkey about with your coordinate systems. However, a precessing orbit is pretty darned Keplerian.
The relationship between the various orbital ...
- 16.2k
7
votes
Accepted
Is it true that the 3 body problem can't be solved using the four basic functions, radicals, and integrals?
In a sense, even solving the two body problem as a function of time is unsolvable in terms of the elementary functions. The problem is that the solution involves the solving for the inverse of Kepler'...
- 33.4k
7
votes
How to get JPL Ephemeris data to work in n-body simulation or why is Mercury flying to Jupiter
I used this n-body algorithm.
Do not use that algorithm, repeated many times over. As a starter, the algorithm uses symplectic Euler. Paraphrasing from the movie "Jaws", "You're going ...
- 33.4k
6
votes
Accepted
Stability of orbital resonance
I am not very familiar with orbital dynamics (so please correct me if I'm wrong). I was told that, for instance in the case of the mean motion resonances that cause the majority of the Kirkwood gaps ...
- 271
6
votes
Accepted
Which will destroy the Earth first: the Sun or Jupiter?
I found an article by Ian O'Neill posted on May 2, 2008 at universetoday.com with the title Could Jupiter Wreck the Solar System? which says
But here’s the kicker: There is only a 1% chance that ...
- 5,526
6
votes
Given mass, position and eccentricity, is there a way to get initial velocity in a 2-body problem?
As previously answered by Connor Garcia, the answer is "No, mass, eccentricity, and position are not enough to determine orbital velocity, even given a specific orbital plane, unless the ...
- 4,696
6
votes
N-body simulation still losing precision despite using arbitrary-precision arithmetic and symplectic integrator
So there are a number of things that can happen here under the proverbial hood that can cause this kind of error to come up.
First off, round off error is going to be at the heart of all your problems....
- 3,394
5
votes
Accepted
Simulation and its necessity in astronomical research
I agree with @uhoh that you don't have to an expert, but above-average knowledge of coding is definitely useful, bordering on "a must". Not for writing huge programs with 1000s of lines, but for ...
- 37k
5
votes
How to scale down solar system data to simulatable values
As barrycarter mentioned in his comment, you should be more concerned with units and less with scale.
Generally, it's best to stick to conventional units that people recognize. (It will keep your ...
- 271
5
votes
Accepted
Trisolar syzygy and it's effects on the planet
Is it just for the spoiler?
My guess is that the 3 suns aligned create a sufficient gravity field for the outermost parts - less well attached - of the planet (atmosphere, people, buildings) to be ...
- 1,452
5
votes
Accepted
Question about the Figure-eight periodic planar three-body motion
There may be some three-body periodic solutions that orbit around a common point, but in general they get a little crazy-looking and may not always contain an immediately obvious center of mass from ...
- 31.4k
5
votes
If an orbit is shifting due to orbital precession, is it still a Keplerian orbit?
Strictly speaking, pure Keplerian orbits can only occur with two bodies obeying Newton's law of gravitation. If there are more than two bodies then the orbits will be perturbed, to some degree.
Kepler ...
- 13.1k
5
votes
Why do people choose 0.2 as the value of linking length in the friends-of-friends algorithm?
A quick search brought me to a book by Houjun Mo, et al. Galaxy Formation and Evolution which says
For example, the frequently used friends-of-friends (FOF) algorithm defines halos as structures ...
- 5,526
5
votes
Accepted
Where to find data on orbits of exoplanetary systems?
One of, if not the most comprehensive exoplanet table is found at exoplanet.eu which also lists the angle of the ascending node and the time of perihelion, time-of-transit, stellar data etc as far as ...
- 17.1k
5
votes
Accepted
Given mass, position and eccentricity, is there a way to get initial velocity in a 2-body problem?
No, this is an underdetermined problem if you don't have the semi-major axis $a$ and orbital inclination $i$ (or some equivalent).
However, if you want circular orbits, then the semi-major axis $a$ is ...
- 16.2k
5
votes
Accepted
Lagrange points for bodies in elliptical orbits?
One of the answers to the researchgate question What are the equation of motion for elliptical restricted three body problem? says:
https://www.sciencedirect.com/search?qs=equation%20of%20motion%...
- 31.4k
5
votes
How to find zero velocity contours for circular restricted 3-body problem in x-y plane?
My second intention behind this post is that how Moulton did this?
To do this the way someone would in 1914, I would start with graph paper and a lattice of points. (x,y) Presumably I would have ...
- 115k
4
votes
How to scale down solar system data to simulatable values
Consider a nearly circular orbit. On average, $ v = 2 \pi r / T $, and the gravitational force balances the centrifugal force:
$$ {G M m \over r^2} = {m v^2 \over r} = {4 \pi^2 m r \over T^2} $$
Solve ...
- 18.2k
4
votes
Question about the Figure-eight periodic planar three-body motion
If this is a possible periodic solution for a three-body problem?
What you've posted here is the classic "figure 8" orbit for a 3 body system. Originally the 3-body system was an unsolvable ...
- 14.9k
Only top scored, non community-wiki answers of a minimum length are eligible