# Tagged Questions

Questions regarding an object 'falling around' another object, due to a combination of gravity and momentum.

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### What are the azimuths of the planets' orbits?

I am creating a virtual solar system model and I want it to be as realistic as possible (e.g. orbits are ellipses, not circles, and orbits are oriented correctly, not all coplanar). In order for me ...
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### Where did this famous Planetary Precession Formula come from?

The following equation (which I shall term the Planetary Precession Formula, PPF for short) famously appeared in a 1915 publication by Einstein where he indicated how it could be derived from his ...
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### Can General Relativity indicate phase-dependent variations in planetary orbital acceleration?

In a previous question about differences in Newtonian and GTR gravitional force for the case of star-planet gravitational interactions an approximate relationship was noted between the expressions for ...
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### Explanation for the mathematics behind Venus' retrograde motion

I've always been interested by the pattern within Venus' orbit around the sun. I found this image and formula of its retrograde motion in the upper right hand corner which confused me. What does it ...
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### Orbiting supermassive black hole or galactic center of mass?

One of the ways they measure the (supposed?) supermassive black hole at the galactic center of the milky way is to measure those tens of stars right at the galactic center that are orbiting what ...
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### Exercise: 2D orbital mechanics simulation (python)

Just a little disclaimer beforehand: I have never studied astronomy or any exact sciences for that matter (not even IT), so I am trying to fill this gap by self-education. Astronomy is one of the ...
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### Is there a standard mapping of symbols to terms for celestial and orbital mechanics

Is there a standard mapping of symbols to terms for celestial and orbital mechanics (and physics in general)? For example here are some ambiguities Angular Momentum: L, H, J, $\Gamma$, Orbital ...
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### How to compute satellite coordinates (lat,long) given antenna's coordinates, angles and satellite height

Given an Earth station (antenna) coordinates (in lat,long) ant its Elevation (El) and Azimuth (Az), how to compute the satellite coordinates (lat,long), known its height? For simplification purposes, ...
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### What would be the dynamics of a double-planet system, similar to Earth / Moon, but with both bodies nearly Earth-sized?

Researching a sci-fi story involving a "twin-planet" system. Is such an arrangement (however unlikely) physically possible? And if so, must they be tidally locked with each other, similar to the moon, ...
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### What is the correct ratio of Newtonian to General Relativistic gravitational effects for Sun + single planet orbital system

For a hypothetical orbital system (Sun + single planet) the Newtonian model and the General Relativity (GR) model produce different expressions for the gravitational effect of the Sun on the planet. ...
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### Is Earth's orbital eccentricity enough to cause even minor seasons, without axial tilt?

I was reading the answers to this question about an exoplanet having seasons without axial tilt, and several responders mention that orbital eccentricity could cause a similar effect, but that the ...
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### Why Earth's perihelion occurs 3rd January rather than 1st?

Why Earth's perihelion occurs 3rd January rather than 1st January? Is there any effort to correct this discrepancy?
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### Is there a lower limit for the altitude of orbiting objects?

As I understand it, one object can orbit another at a variety of altitudes, and the stability of the orbit is determined by (among other things) the speed of the orbiting object. Go too slowly and ...
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I was looking for accurate and up-to-date data regarding the advancement of the perihelion of the planets in the Solar System, the only ones I've found so far are at least 90 years old bout I really ...
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### Is there a general term for epicycles, deferents, and eccentrics in Ptolemaic astronomy?

According to Ptolemy's (c. 150 CE) account of the motions of planets, planets moved in circular paths ("epicycles") around center points that in turn moved around the center of the earth along a path ...
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### How fast is a comet moving when it crosses Earth's orbit?

Is it about the same as Earth's orbital speed?
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### What is the difference between Sphere of Influence and Hill sphere?

Wikipedia's definition of Hill sphere is: An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit ...
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### Can you explain the pattern of Hill sphere sizes of the objects of the Solar system?

I found this image on calculations of Hill sphere for planets/dwarf planets of the Solar system. From http://en.wikipedia.org/wiki/File:Hill_sphere_of_the_planets.png I found it interesting that ...
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### Birthdate differences calculation relative to earths orbit duration

I have got a question as i am trying to figure out what the real difference between the birthdate of my friend and me is. I am born on 1983 6th February 7 am. My Friend is born on 1984 7th February 1 ...
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### The Existence of Natural Satellites in Geostationary Orbits

While browsing through Physics SE, I noticed a question about satellites in geostationary orbit (unrelated to the one I'm asking here), and for a moment I interpreted it as referring to natural ...
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### Are multiple satellites required to handle geostationary orbits?

Do geostationary satellites need to have the equator as the plane of rotation, and the earth's centre to be the centre of rotation? Can it rotate over, say, the Tropic of Cancer, focusing on a single ...
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### Could a habitable satellite of a gas giant have a stable subsatellite?

I have set a science fiction story on a moon, orbiting a gas giant (which orbits its star at approximately the same orbit as the Earth around the Sun), and given this moon its own satellites. The ...
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### How does a gravity slingshot actually work?

From what I know of elliptical orbits, an object speeds up near the periapsis and slows down at the apoapsis, much like we learned in high school physics how a sphere would roll down and back up a ...
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### Is there any point on earth where the moon stays below the horizon for an extended period of time?

When I was teaching a class why the earth has seasons today, I mentioned how the poles of the earth experience months of daylight and darkness. Then one of my students asked whether the moon ...
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### Derivation of the formula for longitude of ascending node for a satellite

I've been looking into the document IS-GPS-200H to understand how to calculate satellite location in the ECEF coordinate. I am having problem understanding the formula to derive $\Omega$, the ...
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### How did Kepler determine the orbital period of Mars?

As I understand it, Kepler used the orbital period of Mars, along with observational data of Mars' and the sun's position in the sky to derive the orbits of Earth and Mars. (As described, here: https:...
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### Finding the radius of an eccentric orbit at any point

Knowing the apoapsis, periapsis and therefore period of an orbit, how can I find the radius of an object in an orbit at a given angle or time, whichever is needed. For example, if I have an object m ...
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### Singularity in Laplace Method for Orbit Determination

I have a question about Laplace angle-only method for orbit determination where the line of sight vectors are being interpolated. I read somewhere that the method fails (due to a matrix being singular)...
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### In 2016, the summer solstice will coincide with a full moon. How often does this happen?

I found that the solstices work on a 400 year cycle based on this. I can't find anything similar for the lunar cycle. Is there a formula I can use to calculate the date of the full moon?
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### Average amount of annual daylight at any place on earth

If this is the wrong group please direct me to the correct one. It seems intuitively obvious that the amount of daylight per annum should be the same for any latitude on earth. For example, 12 hours ...
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### Orbital Elements Transformations

I'm a third year undergrad, and for the project I'm doing this summer, I need to figure out the Earth's position and velocity from the moon's point of view. From the reading I've done, it seems like ...
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### What is the optimal escape trajectory from near a black hole?

Consider a space ship that is being drawn closer to a black hole. The crew begins to notice the effects, and discovers that they are nearing the black hole. They then manage to halt their ...
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### Is there a ceiling for stable L4 or L5 masses?

L4 and L5, the Lagrange points 60 degrees leading and trailing an orbiting body, are famous for being stable. A well known example are the Trojan aseroids at the Sun Jupiter L4 and L5. Nodding to ...
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### Do origin theories imagine each planet to first orbit the Sun very irregularly before stabilizing?

What I was wondering is that, for example, toss a few balls into zero gravity space randomly, what would be the steady state motion? Would not all the balls go on weird directions and undergo ...
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### Does Earth revolves around Milky Way?

As we know Earth rotates around Sun and Sun around Milky Way but then Sun must have some velocity/angular momentum (I don't know that much physics terms). So as Earth revolves around Sun, it must ...
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### When will all eight planets in our solar system align?

Ignoring expansion of the universe, entropy, decaying orbits, and interference from any bodies colliding with or otherwise interfering with their orbits, will the eight planets known planets in our ...
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### Why planet's orbit is not perpendicular or random ?

Why planet's orbit is not perpendicular or random ? It always seems each planet is revolving on the same geometric-plane around the star.
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### Why is the solar system often shown as a 2D plane?

Whenever I have learned about the solar system I always see the orbits displayed as a virtually flat plane. Are all of the orbits in the solar system really like this? If so, why? It seems like a ...
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### Satellite/Planetary Orbits

All planetary orbits contain 5 unusually stable points. These points are particularly important because they allow man-made satellites to orbit the Sun with a period equal to that of Earthâ€™s. 3 of ...
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### What mechanism causes oscillations of the solar system's orbit about the galactic plane?

In a recent paper (news release here) Lisa Randall and Matthew Reece propose that a dark matter disk coinciding with the galactic plane together with the solar system's oscillations through the ...
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### Is there online data on asteroid axial tilts?

I am hoping to find axial tilts for asteroids and also their spring and fall equinox. Some of the asteroids I'm interested in are: 4 Vesta, 1 Ceres, 24 Themis, 65 Cybele, 153 Hilda, 624 Hektor
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### Why are most planetary orbits nearly circular

In our solar system, with the exception of Pluto all planets follow a relatively circular orbit around the Sun, at the same inclination. They also all rotate in the same direction, none are '...
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### What is the orientation of planetary orbits?

I'm working on a planetary motion simulator. I've been working through the equations anomaly, eccentricity, etc. The one thing I'm curious about is if all the ellipses are oriented the exact same way (...
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### Apogalacticon and Perigalacticon

What is the length of the apogalacticon and perigalacticon of the Sun and Milky Way? The general terms seem to be apoapsis and periapsis. My greatest efforts at Googling have failed miserably. If ...
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### Earth's gravitational pull on ISS

How do they make International space station to orbit the earth beyond earth's gravity acting on it? We all know that ISS is rotating at an altitude of just 350km away.How could ISS escape earth's ...
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### Satellite's orbit

What is the maximum distance for a satellite to orbit the earth? Does earth's gravity has the impact on satellite? I do know that earth's gravity will never be zero and it's gravity is inversely ...
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### Locate asteroid in asteroid belt

I was interested in tracking the orbit of 1986 DA. I couldn't find any resource when I looked. Just for fun, so any help appreciated.
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### Asteroids turning out to be Meteorites [closed]

What causes an asteroid to loose control over it's orbit and enter in to another objects atmosphere?