Stationary body or planet in an orbit
- Thread starter arauca
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Fraggle Rocker
Staff member
Absolutely not! It's the tangential motion, which exactly counteracts gravity, that keeps the object in orbit. If it were not orbiting it would simply fall into the central mass.
It is reasonable I just was not sure . You fly or you fall . Thanks
It is possible to orbit a central mass such that it appears to be stationary relative an observer on the central mass... i.e. the satellite is in a geostationary orbit where the orbital period matches the revolution of the central mass.
So if there was a satellite in geostationary orbit pointing a laser directly down on to a point on the equator, then as the satellite moved around its orbit, the laser point would not move as the satellite would always be directly over that same point.
The object does not counteract gravity at all.
It is affected by gravity the same way we are, and it is affected by gravity at all times.
It can react against nothing to be able to counter the action of gravity.
It is merely the combination of gravity and tangential velocity that describes the orbit (or not) that the object takes around the central body.
Sure. Google Lagrange points.
So you guys are saying it is possible . So without going to the prejuditial answer , keep your mind open to the question.
Would it be possible that the earth at some early point in time could be at a large distance from the sun , be stationary and not circulating around the sun ?
Even at Lagrange points the small object would still orbit the larger of the other two objects, in exactly the same period as the smaller of the two large objects.
It is not possible for objects in a 2-body problem to remain at fixed locations in space if only under the influence of gravity.
A geostationary orbit gives the illusion of being fixed but this is merely a result of the orbital period matching the rotation of the planet.
In other 2-body problems, Gravity would cause them to move toward each other, and depending on relative velocities they might end up orbiting.
In a 3-body problem one object may appear to be stationary relative to another, but never with respect to both of the others.
The Lagrange points are merely points where the relative positions of the three objects do not appear to change. But the two smaller ones must still be orbiting the large for this to exist. They are effectively only stationary with regard to a rotating frame of reference.
So you need to understand what people are saying and how it might refer to the example/question you raise before accepting their pronouncements of "it is possible".
Only if the earth was, at some early point in time, not within the sphere of influence of the sun's gravity.
And that it collided with a third object that subsequently pushed it into the sphere of influence, and then collided again (with dust, rocks, planets etc) such that it ended up in a (mostly) circular orbit.
But if we start with the theory that earth formed from the dust around the sun once the sun had formed, then the earth began life in orbit around the sun, and has been in orbit ever since, never stationary, although the orbit has undoubtedly changed over time, especially in those early days.
Thank you for your explanation , It enlightens my ignorance and does not erase the thought of possibility .
Only if:
1) the Sun were orbiting a much larger star and the Earth was in one of its Lagrange points
2) the Earth was very far away from the Sun
In neither case could it then move into orbit without something catastrophic happening (like several collisions with other planets or near passage of a black hole or something.)
But relative to the Sun, then both Earth and the larger star would have the same motion against the celestial sphere of one orbit-per-orbital period, so this isn't a case where the earth is stationary relative to the sun, but only to a coordinate system where the motion of the Sun about the larger star is "factored out." This beggars the notion of stationary.
What do you say about the earth collision with some big body that produced our moon ?
You mean Theia? That impact (if it occurred) was big enough to effectively destroy the Earth; it certainly would have ended any life that existed here (think an entire planet being melted then re-cooling and reforming.)