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# Questions tagged [orbital-elements]

Questions about the parameters needed to specify the characteristics of an orbit.

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19 votes
4 answers
5k views

### What are "non-Keplerian" orbits? What are some familiar examples in our solar system, and can some still be closed?

This excellent answer to Forms of stellar orbits around the galactic center invokes the following concepts: non-Keplerian orbits closed orbits I have a fairly good idea what these mean and so might ...
• 30.2k
77 votes
4 answers
10k views

### How does the Earth move in the sky as seen from the Moon?

I just want to be sure I am visualizing this correctly, because it seems odd. The Moon is tidally locked to the Earth but there are wobbles to its motion due to libration. So from a point on the ...
• 1,569
17 votes
1 answer
491 views

### Orbital velocity of a planet - why is my calculation off by about 10%?

I am not sure if I am doing something wrong, or misunderstanding Reider and Kenworthy (2016). I'm just trying to reproduce the orbital velocities listed in Table 1. The second paragraph of Section II ...
• 30.2k
8 votes
2 answers
1k views

### How do I calculate the positions of objects in orbit?

In a model of the solar system, given the Sun is at the point $(0, 0, 0)$, an given the six orbital elements for each object in orbit ($a$, $\epsilon$, $i$, $\Omega$, $\omega$, $M_0$), how can I ...
• 295
5 votes
1 answer
1k views

### Simulate an orbit with orbital elements

I want to simulate the orbits of the planets from our solar system. I want to use orbital elements to calculate the current position(xyz) at a time t. The simulation doesn't have to be too exact, but ...
• 53
4 votes
2 answers
2k views

### What is exactly the "longitude of the perigee"

Some moon phase calculation algorithms (apparently derived from Duffet-Smith's book, example here) seem to use a parameter called "longitude of perigee at epoch". What exactly is this? Can I assume ...
• 143
4 votes
1 answer
327 views

### How do times of lunar standstills vary over time? If we folded them back into a lunar month plot, would they have "prograde and retrograde motion"?

The recent question Are lunar phases and lunar standstills in sync with each other? brought me to a standstill because I don't fully know what a lunar standstill is. It's one of those words like "...
• 30.2k
2 votes
1 answer
292 views

### Time taken calculation to reach synodic degrees between planets

I have a software tool which calculate the synodic period with degree inputs with two planets. Synodic Period is the temporal interval that it takes for an object to reappear at the same point in ...
• 45
9 votes
3 answers
467 views

### Asteroids conjunction

I am currently writing a C++ program to show asteroids in 3D, and find close approaches or collisions. I got my orbital elements from JPL https://ssd.jpl.nasa.gov/sbdb_query.cgi. So far so good, with ...
• 399
8 votes
2 answers
256 views

### If the hypothesized planet behind the Kuiper belt existed, would it have a barycenter outside the Sun?

In 2016, an additional object rotating our Sun has been suggested. Assuming it has 5 Earth masses, would the planet or black hole proposed by Brown and Batigyn have a barycenter within the Sun or ...
• 1,538
8 votes
1 answer
556 views

### Why is Neptune true anomaly decreasing?

So I've been having fun with trying to determine where the perihelia of different planets are (using JPL Horizons). And by the time I got to Saturn, something weird started happening. I've noticed ...
• 158
7 votes
1 answer
779 views

### Forms of stellar orbits around the galactic center

Do all stars in orbit around Sagittarius A have approximately circular orbits or are there stars that orbit the Milky Way center very elliptically, like being in the Milky Way's outer rim at apoapsis ...
• 263
6 votes
1 answer
208 views

### Is there a preference for orbital planes of planetary systems to be aligned with the galactic disk?

I'm not sure for how many planetary systems we have a fairly good idea of the inclination and "argument of periapsis" of the orbital plane. I'm assuming there are a number of them that we can estimate ...
• 2,962
6 votes
3 answers
1k views

### "Periapsis" or "Periastron"?

I was taught from Bate Mueller and White, that the proper terms for the closest and furthest points and distances from a body in orbit around another unspecified body are "periapsis" and &...
• 16.3k
4 votes
1 answer
281 views

### How to translate from local laplace plane to ecliptic J2000 (or ICRF)

The NASA JPL websize gives mean orbital elements for e.g. Iapetus or Titan in relation to the local laplace plane. ...
4 votes
2 answers
690 views

### Sun's orbital elements

I have the orbital elements of an asteroid's heliocentric motion (the orbit has non-zero inclination and is elliptical). But I want to simulate the motion of the sun around the asteroid. So without ...
• 41
3 votes
1 answer
547 views

### Calculate apsides without knowing eccentricity

How would one go about determining the apsides of an orbit, knowing only the current distance between the 2 bodies, the orbital velocity, and the period? Every formula I've seen requires eccentricity, ...
3 votes
2 answers
756 views

### What is the effect of the axial precession on the orientation of the planet's orbits?

I am working on an online application to visualize the positions of the planets and to calculate their ephemerides (you find it here, but it is not complete yet). I do not have much knowledge in ...
• 61
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 ...
3 votes
1 answer
4k views

### How Wide is Earth's Roche Limit?

My question is simple: Given the gravitational relationship between Earth and the moon, how wide is Earth's roche limit? How close does the moon have to orbit before getting disintegrated by Earth's ...
• 393
2 votes
0 answers
104 views

### Does habitable zone take tidally locked bodies into account?

Imagine a tidally locked planet orbiting a red dwarf, where habitability is not situated close to terminator zone, but on a "small" cap normal to incident starlight (zenith) with permanent average +15 ...
2 votes
1 answer
622 views

### Orbital speeds of Components of Binary System

How does one calculate the orbital speed s of the members of a binary system? Iirc, the average separation of Alpha Centauri A and B is 23 AU, but the orbit is highly elliptical, so that the ...
• 511
1 vote
1 answer
652 views

### How Can I Interpolate Ephemerides?

I have two ephemerides for orbital elements—that is, each contains $a$ (semi-major axis), $e$ (ecc.), $i$ (incl.), $\Omega$ (long. asc. node), $\omega$ (arg. of peri.), $\tau$ (time of peri.), $T$ (...
• 433
1 vote
1 answer
128 views

### State vectors of "interesting" multiple stars

I'd like to show a demonstration of Runge Kutta integration of real systems using examples of interesting multiple stars, where "interesting" means you can see through a small telescope that they are ...
• 30.2k
1 vote
1 answer
428 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'...