# What is Retrograde: Definition and 14 Discussions

Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or nutation of an object's rotational axis. Prograde or direct motion is more normal motion in the same direction as the primary rotates. However, "retrograde" and "prograde" can also refer to an object other than the primary if so described. The direction of rotation is determined by an inertial frame of reference, such as distant fixed stars.
In the Solar System, the orbits around the Sun of all planets and most other objects, except many comets, are prograde, i.e. in the same direction as the Sun rotates. Except for Venus and Uranus, planetary rotations are also prograde. Most natural satellites have prograde orbits around their planets. Prograde satellites of Uranus orbit in the direction Uranus rotates, which is retrograde to the Sun. Nearly all regular satellites are tidally locked and thus have prograde rotation. Retrograde satellites are generally small and distant from their planets, except Neptune's satellite Triton, which is large and close. All retrograde satellites are thought to have formed separately before being captured by their planets.
Most low-inclination artificial satellites of Earth have been placed in a prograde orbit, because in this situation less propellant is required to reach orbit.

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1. ### A Question for Distant Retrograde Orbit in CR3BP

In the Sun-Earth system in circular restricted three body problem, how can i define the initial conditions for a distant retrograde orbit? The state vector has to be X=[x0 0 0 0 vy0 0]. How i define the initial position in x-direction and the initial velocity in y-direction.? What values do i...
2. ### I Retrograde Planets? - CPtolemy

Hi I was wondering: if we know the geocentric coordinates of the sun and one planet (longitude and distance) in one instant only, can we calculate/know mathematically if the planet is in retrograde motion or not? Or must we have 2 observations? Clear skies CPtolemy
3. ### How do I solve for the angle, as a function?

Homework Statement Homework Equations [/B] The two equations in the image, as well as (maybe) standard vector operations like dot product, cross product. The Attempt at a Solution [/B] So, I've tried to do what my instructor suggested and put everything in terms of Earth (Using RE and TE...
4. ### I Can anyone tell me if 2009 MS9 is prograde or retrograde?

I'm constructing a theory on the origin of extreme trans-neptunian objects. Can anyone tell me if 2009 MS9 is prograde or retrograde in its orbit? (and show me where you found this information out). I can't for the life of me find it anywhere. Thanks.
5. ### I Direct vs. Retrograde Precession

(This is not about the motion of the planets.) If one takes a body in space (not outer space, necessarily) with only central forces, it may exhibit one of two types of precession: direct or retrograde. If the body is flat, the precession is retrograde: the spin and precession rates have...
6. ### I What causes retrograde rotation in planets and moons?

When I googled it, I wasn't satisfied with the answers from various sites...some sites like universetoday.com gave me a glimpse but it was totally theoretical and based on assumption. Also I would like to know why some planets have retrograde rotation; what might have caused them to and why do...
7. ### B Retrograde star orbits in the Milky Way

Are there any stars in the solar neighborhood that orbit the galactic center in the opposite direction?
8. ### A Retrograde planets enumeration

Is it mandatory for any planetary system like our Solar system to have a retrograde orbit planet in it's midst ? Is there any upper limit for the same ?:))
9. ### Retrograde Motion: What is it & How Does it Work?

What is retrograde motion? Can some one explain this movement while Earth is constant and the outer planet is moving with relative rotational speed.

How can we relate mathematically the time interval in which a planet is in retrograde motion and the devided distances from the sun of the planets ? My first drawing was this: Where S is thee sun , P is the planet, T si the Earth. The v's are the corespondent speeds If we take a look at...
11. ### What is retrograde planetary perihelion precession?

I know what each word mean independently, I'm just confused as to what sort of motion is trying to be described as a whole.
12. ### Retrograde Motion: How Tilting of Moon Affects Revolution

How is the tilting of a moon affects its revolution with its primary
13. ### A New Explanation for Venus' Retrograde Rotation

Consider this scenario: a Mars-size object strikes a glancing blow at Venus's backside that's facing toward the Sun. The resultant debris cloud would then coalesce into a large moon having a retrograde orbit. Tidal friction would then slow down Venus' rotation until it was tidally locked to its...
14. ### Venus Retrograde Rotation Redux

I think I might have a possible explanation for the peculiar, west-to-east rotation of Venus, where a day is longer than a year. :rolleyes: Venus "wants" to have one side always facing the sun, so that one rotation would equal one revolution (like the Moon). However, once Venus achieved this...