Given the rotation of all gravity bodies, does the Earth ever return to the same point in space?
Planet orbit question
- Thread starter ThunderAeroI
- Start date
"Same point" in what sense? There's no such thing as a fixed point in space. Every point is relative to some other point, and everything is always in motion.
I guess I was thinking that since the Earth rotates the sun annually some might think that means every December or on some date the Earth would be in the same spot in space. The spot being based on where it was before and not based on the sun being the center, etc.
I'd say no. At no point is the Earth ever in the same spot, but since everything is gravity bound it would seem as though we do revisit the same space spot annually.
Is there anyway to know how far we have moved and in what direction for any given period?
I'd say no. At no point is the Earth ever in the same spot, but since everything is gravity bound it would seem as though we do revisit the same space spot annually.
Is there anyway to know how far we have moved and in what direction for any given period?
The whole galaxy is moving relative to all of the other galaxies. The solar system is moving inside our galaxy relative to all of the other star systems and around the core of the galaxy. The Earth is orbiting around our sun (which is also not completely stable, but wobbles a bit in it's spin) in an elliptical orbit so...
I very much doubt that the Earth has ever been in exactly the same place twice in 5 billion years...
Ok - couldn't resist this:
I very much doubt that the Earth has ever been in exactly the same place twice in 5 billion years...
Ok - couldn't resist this:
The way I see it is this..
Our planets orbit our sun
Our sun orbits the galactic center
Our galaxy orbits the universe..
And if you looked at it from outside it would look like a clock
Our planets orbit our sun
Our sun orbits the galactic center
Our galaxy orbits the universe..
And if you looked at it from outside it would look like a clock
Relative to the sun? Yes.
Relative to the moon? Also yes.
Relative to other planets in the solar system? Yes (far less often, but once every, say, hundred thousand years or so?)
Relative to other stars in the galaxy? No.
Relative to the galaxy as a whole system? No.
Relative to the barrycenter of the Milkyway/Andromeda gravitational interaction? No.
Relative to the center of the galaxy? No.
Relative of my grandfather? Funny story. See, what happened was...
Relative to my mother in law? Ask me again after coffee.
Relative to my dog? Yes, depending on the scalar quotient of rotational inertia squared over the cosine to the third powSQUIRREL!
There is no fixed or universal reference frame, any "point in space" is only defined relative to a particular object that, for measuring purposes, can be considered "stationary." The truth is, ANY object can be said to stationary in any point of reference and it is then true that EVERYTHING ELSE is moving with respect to that object. While the laws of motion tell us that certain interactions will balance around a particular center (e.g. the center of the solar system, around which all gravitationaly bound objects will orbit in predictable ways), describing those motions still depends on a fixed reference point with which to make those kinds of measurements.
As for the overall question:
The calculations of "one full revolution around the sun" were originally based entirely on the cycle of the seasons. The idea being, the tilt of the Earth's axis is believed to be pretty consistent during its revolutions. We know this because for thousands of years we have been measuring the time between sunrise and sunset and come up with days like the solstice and the equinox when there is either a maximum or mimimum or equal period of daylight and night time. Each solstice or equinox, one COULD say that the Earth has returned to the same position, relative to the sun, that it was in previous years. We also check against the background stars at night and their relative positions in the sky relative to fixed points on the Earth's surface and we discover that, yes, the stars are in about the same place every year when those special days happen, so we're either at the same place or pretty close to it.
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In short, relative to the Earth? All the time.
The beautiful people, the beautiful people,
It's all relative to the size of your steeple
It's all relative to the size of your steeple
If the big bang happened at a single point, would everything orbit that point, or just be travelling away from that point & eventually back towards that point.
Yes
No it does not retrace the path. All the other objects in the solar system preturn the orbit. It is not an ellipse.
^+1 The perihelion of the Earth advances by just over 11 arc seconds per year, so no even if an absolute reference frame existed. As there is no absolute reference frame the question is meaningless anyway.
Which means that Earth's perihelion advances completely around the sun (assuming a measureable fixed coordinate system that doesn't really exist) every 327 years, at which point, yes, Earth would basically retrace the same path through space that it did 327 years ago.
No the orbital parameters are constantly changing. The orbit is not a precessing eclipse, but approximated by one at a specific time.
Yeah, the eccentricity, perihelion, aphelion etc of the Earth's orbit change over time. In any case, the whole solar system is moving in the general direction of Vega, the Milky Way towards the Andromeda galaxy etc.
As does perihelion and aphelion distance also vary by several hundred kilometers from one orbit to the next, influenced by perturbations from nearby planets (most notably, Jupiter). And it gets even weirder when you consider that the SUN actually orbits around a barrycentric point due to Jupiter's interaction, so the sun may not even be in the same position as it was before, 327 years ago, because Jupiter is in a different place in its orbit.
But that cycle is close enough for our purposes in evaluating this ridiculous thought experiment (see my first post in this thread).
