Questions tagged [orbital-elements]

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

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3 votes
0 answers
97 views

Kepler to Cartesian and Cartesian to Kepler inaccuracies

I am programming a computer simulation set in a star system. I've used Rene Schwarz's wonderfully concise memorandi explaining converting from Kepler orbital elements into cartesian coordinates and ...
3 votes
1 answer
152 views

Is it possible to determine orbit orientation of exoplanet without direct imaging and astrometry?

Is it possible to determine orbit orientation (in space) of an exoplanet without direct imaging or astrometry (for example with transits and rv observations only)? I have read somewhere that orbits ...
2 votes
1 answer
60 views

Calculating Ephemeris from JPL Osculating Element

I've built some open source software that calculates Ephemeris from JPL osculating elements to simplify imaging and tracking of Comets, Asteroids, and Near-Earth bodies. This works very accurately a ...
5 votes
3 answers
567 views

Which star system has the highest multiplicity (# of stars), whose orbits are known for all stars?

I posed a question on here a couple months or so ago about the orbital patterns of each of the seven stars in the two septuple star systems Nu Scorpii and AR Cassiopeiae. It went unanswered for more ...
2 votes
1 answer
78 views

Can there be multiple periapsides?

Consider the following image of a barycentric orbit of a binary star system. I could draw their relative orbits by drawing a line connecting both bodies at each point in their rotation. In this ...
4 votes
1 answer
258 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. ...
1 vote
1 answer
70 views

What is the duration of a year on the Moon (Tropical/Sidereal period) for orbit about the Sun ? How/why does length of lunar days vary ? Soltices?

The inclination of the lunar equator to the ecliptic is 1.543°. Synodic period or Length of a day on the moon = 708.7344 hours Moon Fact Sheet 100 Lunar Days - Parts I and II
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 ...
2 votes
1 answer
119 views

Are the rotational axes of Earth and Mars parallel?

So I was stuck on a question involving the transformation of coordinates from geocentric to Mars-centric coordinates. The relative position of Mars and its orbital details are given. I thought that we ...
2 votes
0 answers
113 views

Code for Gauss's method orbit determination

I'm trying to calculate the state vectors of the ISS using Gauss's method with three sets of values (right ascension, declination and sidereal time). I'm following the method described in "...
5 votes
0 answers
173 views

Why does the tropical year have a ~161 years cycle?

Using PyEphem, I calculated the time difference between consecutive summer solstices in the south hemisphere for the last 4000 years, and plotted them in a graph. It seems like random noise around the ...
2 votes
0 answers
89 views

Find position of orbiting body along orbit efficiently

I'm coding a game, and a fundamental mechanic is celestial bodies moving in elliptical, Keplerian orbits around a single gravitational point in a planetary system (not our solar system). The bodies ...
1 vote
1 answer
212 views

Calculating the parameters of binary systems?

If I know the masses of the two bodies (they have equal mass), how do I calculate the two ellipse eccentricities, length of the apoapsis and speed at the apoapsis, that make stable system, as in this ...
2 votes
1 answer
391 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 ...
3 votes
1 answer
264 views

Orbital period of a planet orbiting Delta Pavonis in habitable zone

I'm continuing my inquiry about the fictional planet I have described here: https://worldbuilding.stackexchange.com/questions/231162/length-of-seasons-on-a-planet-with-eliptical-orbit. I'm now settled ...
4 votes
1 answer
257 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 "...
2 votes
0 answers
63 views

Is there an orbit around the earth that experiences a total solar eclipse by the Moon at least every month?

Is there a way to design an earth orbit so that it passes through the Moon's umbra with greater frequency than total solar eclipses occur on earth's surface? What is the maximum frequency of eclipses ...
8 votes
2 answers
250 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 ...
3 votes
1 answer
103 views

Time of comet at perihelion query

In Practical Astronomy With Your Calculator Or Spreadsheet by Duffett-Smith and Zwart, the authors write (in relation to calculating cometary positions): The longitude of the comet is not usually ...
5 votes
0 answers
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A couple of questions about Earth's hypothetical planetary rings

From what little I know of this subject, It should be possible for Earth (Or a planet the size of Earth) to keep a system of Planetary Rings. However, looking around the internet only gives me info ...
-4 votes
1 answer
1k views

Help me better understand how the plane of Moon's orbit around Earth behaves

Is the plane in which Moon orbits around earth, inclined with respect to earth's equatorial plane? If yes, is it constant or does it change with time? If it changes, how much time does it take to make ...
7 votes
2 answers
2k views

What are the orbital velocities of the other planets? For objects in a 'Low-Earth-Orbit' around planets other than Earth, e.g.?

I was pondering this question recently, but most sites I can find only mention the speeds/velocities of the planets around the Sun when I look for 'orbital velocities' of the planets. I tried ...
2 votes
1 answer
268 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 ...
5 votes
1 answer
281 views

Question about Cowell's method

According to Wikipedia: “ ... for $n$ mutually interacting bodies, Newtonian forces on body $i$ from the other bodies $j$ are” given by the summation equation$$\ddot{\mathbf{r}}_{i}=\sum_{j=1,j\neq i}^...
5 votes
1 answer
433 views

Orbital modelling, three bodies, leapfrog numerical integration

Apologies for the length of this question. I'm modelling the motion of a single planet around the Sun using the equations: $$dv_{x_{i}}/dt=a(t)=-GM_{SUN}x_{i}/r^{3},$$ where $x_{1}=x$, $x_{2}=y$ and $...
2 votes
1 answer
134 views

Orbital modelling - best choice for initial JPL Horizons data?

I'm modelling planetary orbits using a spreadsheet and Feynman's numerical method given here. I have put together a spreadsheet (10,000 rows) to model Mars' orbit in three $\left(x,y,z\right)$ ...
1 vote
1 answer
163 views

Calculate how many days left for synodic period from particular planet

One of the many tools used in Astronomy are the formulas used to determine Orbital Motion. There are two basic forms of orbits: Sidereal Period Synodic Period For Jupiter: $$\mathrm{\frac{1}{P} = \...
2 votes
0 answers
246 views

What is the relationship between true anomaly and solar longitude?

So, my ultimate objective is to map solar longitude values onto a pseudo-Gregorian calendar. I thought this would be simple, but it has turned out to be anything but. I have asked several questions on ...
4 votes
0 answers
205 views

How to determine the time of periastron passage (T) of a single lined spectroscopic binary?

I am working on finding spectroscopic elements of a single lined spectroscopic binary. All I have is irregularly spaced radial velocity data which needs to be phase folded to plot a velocity curve (RV ...
7 votes
1 answer
317 views

Earth-Moon Barycenter Perihelion

I am trying to implement an algorithm I created to get the sun rise, transit and set accurately, but in order to do that I need to get the Earth-Moon barycenter (EMB) perihelion, and not the Earth ...
1 vote
2 answers
182 views

Planet's distance data from JPL Horizons - Mars Curiosity mission

I am looking for distance measurement in AU between planets and Earth. E.g. For Mars, Current distance, or distance of Mars from Earth at any given datetime, along with minimum (closest approach), ...
10 votes
1 answer
3k views

Why is the L1 point (Lagrange) almost 1 million miles from Earth? Shouldn't it be closer to us?

Try to follow my simple logic: The Sun is almost exactly 333,000 times as massive as Earth, and gravitational strength increases linearly with mass, so the Sun's gravity is about 333,000 times ours. ...
4 votes
2 answers
203 views

Accuracy of Laplace Method for determining orbital elements

Recently I had to implement the Laplace method and apply it to 3 observations of Mars (10 days in between two observations). The results were pretty good, with discrepancies with real data well below ...
2 votes
1 answer
384 views

What is the difference between inclination and obliquity?

I'm trying to understand the differences between obliquity and inclination when it comes to a system of a planet orbiting a star. From what I understand, obliquity is the angle between the orbital ...
28 votes
2 answers
6k views

Is the science in "Don't Look Up" realistic?

In the new movie "Don't Look Up", astronomers discover a comet in the outer Solar System that's going to hit the Earth about 7.5 months later. I think they calculate its trajectory within a ...
8 votes
1 answer
487 views

Post-Keplerian orbital parameters; is there a generally accepted set with definitions?

Strong-Field Gravity Tests with the Double Pulsar is a pretty big deal! 16 years of precision timing including "timing parallax" via VLBI has provided a dataset for which analysis requires (...
2 votes
1 answer
296 views

Does the .43 arc-second per year deviation of Mercury's orbit from Newtonian predictions mean that its position is 'off' by 75 miles per year?

If I divide the elliptical circumference of Mercury's orbit by .43 arcseconds, I get an answer of almost exactly 75 miles.... BUT, it is the precession of the periapses that is off, not 'just' its ...
9 votes
3 answers
2k views

How does NASA figure out orbital period and mass data for planets and other celestial bodies?

Does NASA calculate orbital periods using Kepler's Laws, or do they measure and observe it in some way? If the latter, how do they do so? Similarly, does NASA calculate the mass of bodies using Kepler'...
0 votes
1 answer
191 views

Using Kepler's 3rd law to calculate $\mu$ (standard gravitational parameter)

I'm trying to calculate $\mu$ (the standard gravitational parameter) with this formula $\mu = 4\pi^2a^3/T^2$ I'm using Earth's orbit is $a=1$ and $T = 365.2564$ for $a^3/T^2$ I'm getting $\approx7.496$...
8 votes
1 answer
1k views

Could Planet X have a perihelion much closer than 300 AU and still be responsible for the gravitational interaction with 19 TNOs?

In August, Michael Brown and Konstantin Batigyn proposed new data concerning the hypothetical Planet X to explain the orbits of the 19 TNOs. They suggest a perihelion of 300 AU, but might Planet X be ...
9 votes
3 answers
457 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 ...
5 votes
1 answer
1k views

Confused on how you are supposed to calculate eccentricity without apsides

I'm kinda confused on how to calculate either the apsides or the eccentricity without knowing one or the other. Let's say you have an object in orbit around another. If you know the current distance, ...
5 votes
1 answer
102 views

Have we indirectly measured GW driven orbital decay in anything besides binary pulsars?

Binary systems decay for all sorts of reasons. I'm asking specifically about orbital decay due to gravitational wave emission. All of direct GW detections of binary systems have come with orbit ...
2 votes
0 answers
292 views

What's the formula for change in argument of periapsis over time due to J2 perturbations for a geocentric satellite?

I'm trying to propagate the orbit of the ISS, but it became very clear to me very quickly that the J2 perturbations were nothing to scoff at. A quick google search gave me the equation for the change ...
3 votes
0 answers
60 views

Precision of orbital period of exoplanets vs solar system planets (Extrasolar Planets Encyclopedia)

I noticed that the Extrasolar Planets Encyclopedia lists the orbital period of L 98-59 b in days to 7 decimal places. Can astronomers really measure orbital period of exoplanets to greater precision ...
3 votes
2 answers
379 views

What are the values of the Mean Anomalies of the planets in the Solar System?

I am trying to find a list of all the Mean Anomalies of the planets in the Solar System at the Epoch Jan 2000. I tried to Google it up but couldn't find any result. Can you please share the values or ...
2 votes
0 answers
79 views

When an object revolves around an oblate planet, in near-circular orbit, does the oblateness ALWAYS make it moves FASTER?

tl;dr: The orbital period for a Keplerian orbit of a small body around a massive one with standard gravitational parameter $\mu=GM$ and semi-major axis $a$ is given by $$T = 2\pi\sqrt{\frac{a^3}{\mu}}....
4 votes
4 answers
9k views

Can one approximate the semi-major axis of an orbit as the average orbital distance for eccentric orbits?

Kepler's 3rd Law (regarding the relation between orbital period and the semi-major axis of an orbit) applies to all elliptical orbits. But as I understand it, the only reason it is safe to use the ...
3 votes
1 answer
111 views

Querying MPC data : P and Q vectors of any use to compute the eccentricity vector?

While querying the Minor Planet Center orbital data for asteroids, among the returned data, I noticed 6 variables corresponding to x,y and z components of two 3-D vectors namely P and Q. The ...
6 votes
3 answers
398 views

Kepler's Law, focal points - Heliocentric or Barycentric?

It is known that all the mass in the Solar system moves around the Barycenter. For the two focal points in Kepler's law; is the first focal point $F_1$ a Heliocenter? Or is it actually a Barycenter? ...