Stargazing Does anyone know where Earth's gravity stops and space begins?

[fascinated]

HI all! Clearly a noob here. The title says it all. I can't seem to find anything. Thanks for any help, folks.

 

[Ibix]

It doesn't. Gravitational influence is infinite ranged as far as we are aware. You can find a surface where the Earth's gravity becomes less than that of the Sun, for example, and define that as the edge of the Earth's influence, but it's fairly arbitrary.

Usually, space is defined more in terms of whether there's atmosphere. The Earth's atmosphere is pretty negligible above 20km, the defined upper edge of the atmosphere is higher - 50k to 100km up, I believe - see Wiki's article.

 

[fascinated]

It doesn't. Gravitational influence is infinite ranged as far as we are aware. You can find a surface where the Earth's gravity becomes less than that of the Sun, for example, and define that as the edge of the Earth's influence, but it's fairly arbitrary.

Usually, space is defined more in terms of whether there's atmosphere. The Earth's atmosphere is pretty negligible above 20km, the defined upper edge of the atmosphere is higher - 50k to 100km up, I believe - see Wiki's article.

So, does that mean that Earth's atmosphere technically extends to the sun? Even beyond?

 

[fascinated]

Sorry if you thought I was being smart, but I am familiar with the Karman line. It's that we know now that :
"The moon flies through Earth's atmosphere,..."
https://www.space.com/earth-atmosphere-extends-beyond-moon.html

 

[davenn]

So, does that mean that Earth's atmosphere technically extends to the sun? Even beyond?

HUH ?

You asked about the Earth's gravity and you were given the correct answer

now you have suddenly switched to Earth's atmosphere
There isn't a defined line boundary of where the atmosphere stops, is slowly dies out at ~ 300 - 400km above the Earth's surface
Google will give better numbersDave

 

[davenn]

"The moon flies through Earth's atmosphere,..."

no it doesn't, don't mis-quote the article !
I can see from that article that I wasn't too far out

Earth's atmosphere is about 300 miles (480 kilometres) thick, but most of it is within 10 miles (16 km) the surface.

so that article answers your second Q ... dies out at ~ 480km

Dave

 

[Delta2]

As others said, theoretically Earth's gravity extend to infinity (if the universe is infinite). However it gets weaker and weaker as it extends farther and farther. My rough calculations say that at a distance of 64000km from Earth's center and into space , Earth's gravity becomes only 1% of the strength it has at the surface of earth.
If your next question is going to be, then how come in the international space station, much closer than 64000km, astronauts appear to be weightless, the answer is that they have around 70-80% of the weight they have at the surface of the earth, but their weight acts as centripetal force that keeps them in circular orbit and not as a force that will pull them down.

 

[fascinated]

Thanks for the info, but I'm still confused, lol.

You asked about the Earth's gravity and you were given the correct answer

now you have suddenly switched to Earth's atmosphere

Right, because where gravity stops is where our atmosphere ends by definition, no?

now you have suddenly switched to Earth's atmosphere
There isn't a defined line boundary of where the atmosphere stops, is slowly dies out at ~ 300 - 400km above the Earth's surface
Google will give better numbers

I read the article. It says "about." And google has no better answer that I could find, hence this thread, lol.

no it doesn't, don't mis-quote the article !

I didn't, please.

so that article answers your second Q ... dies out at ~ 480km

Again, it says "about" and I was looking for more. If we don't know, we don't know and that is fine. I am really trying to find out IF we know, if that makes more sense.

Earth's gravity becomes only 1%

Right, but I don't care about that. I am interested at the exact point where our atmosphere ends (if this point is known).

Thanks again for the responses and any help here.

 

[Ibix]

Right, because where gravity stops is where our atmosphere ends by definition, no?

No. Gravity and atmosphere are unrelated - for example the Moon has gravity but no atmosphere.

Again, it says "about" and I was looking for more. If we don't know, we don't know and that is fine. I am really trying to find out IF we know, if that makes more sense.

The point is that there isn't really a sharp cutoff. It isn't a case of "we don't know", it's a case of "how do you define no atmosphere". There is never a point when you are in perfect vacuum, because there's gas even in interstellar space. That's not the atmosphere, but the exact height at which atmosphere stops and interplanetary medium starts is a matter of definition rather than absolute scientific fact. That's why you see different heights - different people use different definitions.

 

[fascinated]

"how do you define no atmosphere".

I am looking for where the Earth's gravity can no longer affect the particles in our atmosphere or where Newton's 2nd law takes over and equilibrium occurs. I may be defining things incorrectly for which I apologize.

 

[fascinated]

No. Gravity and atmosphere are unrelated - for example the Moon has gravity but no atmosphere.

The moon has a thin atmosphere.

 

[russ_watters]

I am looking for where the Earth's gravity can no longer affect the particles in our atmosphere or where Newton's 2nd law takes over and equilibrium occurs. I may be defining things incorrectly for which I apologize.

There is no such limit. I'm not sure why you aren't grasping what has been said about how gravity works. Can you state clearly your understanding of this issue for gravity, without considering the atmosphere?

Also, I don't know how you think Newton's 2nd Law applies... or rather why don't think it applies in the atmosphere. Can you explain?

There's probably a limit to where the density and motion of particles is dominated by solar wind. It could be the article answers your question, though: 390,000 miles.

 

[fascinated]

There is no such limit. I'm not sure why you aren't grasping what has been said about how gravity works.

If there is no limit, then that would make sense.

Can you state clearly your understanding of this issue for gravity, without considering the atmosphere?

Not really as it is gravity that allows us to have an atmosphere to breathe.

Also, I don't know how you think Newton's 2nd Law applies... or rather why don't think it applies in the atmosphere. Can you explain?

It could be the article answers your question, though: 390,000 miles.

I know it could be, but appears there is nothing concrete.

 

[russ_watters]

Not really as it is gravity that allows us to have an atmosphere to breathe.

No, what I mean is, how gravity works for other things besides the atmosphere. For example, can you explain for example how gravity affects spacecraft a long distance from Earth? Once you make sure you have that correct, then you can apply that to the atmosphere.

View attachment 264019

That picture does not answer my question. [edit] Worse, it seems to lead in a wrong direction if you think it is relevant here...

 

[fascinated]

No, what I mean is, how gravity works for other things besides the atmosphere.

The Earth's mass is curving spacetime and everything must follow that line?

For example, can you explain for example how gravity affects spacecraft a long distance from Earth?

This is part of what I am examining... or trying to.

That picture does not answer my question. [edit] Worse, it seems to lead in a wrong direction if you think it is relevant here...

THIS! Please explain.

 

[russ_watters]

This is part of what I am examining... or trying to.

Then explain! We can't tell you if the idea that you have in your head is right or wrong if you won't tell us what that idea is!

I'll make it very concise: A spacecraft is a million km from Earth and stationary with respect to Earth. It shuts off its engine. What happens?

THIS! Please explain.

You said that picture discusses Newton's 2nd Law. You need to tell me why. I can't explain what you haven't told me! You may as well post a picture of a cat and ask me to explain it.

 

[fascinated]

I'll make it very concise: A spacecraft is a million km from Earth and stationary with respect to Earth. It shuts off its engine. What happens?

It follows the curvature of spacetime.

You said that picture discusses Newton's 2nd Law. You need to tell me why.

energy has an absolute unfailing tendency to go from "more concentrated" to "less concentrated"
https://www.ftexploring.com/energy/2nd_Law.html

 

[russ_watters]

It follows the curvature of spacetime.

Keep this Newtonian and try again.

energy has an absolute unfailing tendency to go from "more concentrated" to "less concentrated"
https://www.ftexploring.com/energy/2nd_Law.html

That isn't Newton's 2nd Law. So which did you mean? And explain. Use your words.

 

[fascinated]

Keep this Newtonian and try again.

Never mind, friend. I am looking at this from our current knowledge base. We have not believed in "mass attracting mass" for over a century. Heck, we never did, really.

From the man himself:

Food for thought here...

Tis unconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon & affect other matter without mutual contact; as it must if gravitation in the sense of Epicurus be essential & inherent in it. And this is one reason why I desired you would not ascribe {innate} gravity to me. That gravity should be innate inherent & {essential} to matter so that one body may act upon another at a distance through a vacuum without the mediation of any thing else by & through which their action or force {may} be conveyed from one to another is to me so great an absurdity that I believe no man who has in philosophical matters any competent faculty of thinking can ever fall into it...

--Original letter from Isaac Newton to Richard Bentley
http://www.Newtonproject.ox.ac.uk/view/texts/normalized/THEM00258

That isn't Newton's 2nd Law.

If that teaching link is wrong, please explain why.

 

[russ_watters]

Never mind, friend. I am looking at this from our current knowledge base.

Evidently you haven't taken any physics in school yet. That's not how it works. Heck, that isn't how NASA works.

If that teaching link is wrong, please explain why.

The link is about the 2nd law of thermodynamics, not Newton's second law of motion.

Im starting to question whether you are really trying to learn anything here or not. You need to put more effort into this if you want help.

 

[fascinated]

Evidently you haven't taken any physics in school yet. That's not how it works. Heck, that isn't how NASA works.

Please explain then; this is important.

The link is about the 2nd law of thermodynamics, not Newton's second law of motion.

Im starting to question whether you are really trying to learn anything here or not. You need to put more effort into this if you want help.

I know what the link is about and it is EXACTLY what you asked about.

 

[russ_watters]

Please explain then; this is important.

NASA uses Newton's Law of Gravity to navigate spacecraft and if it's good enough for them, it is good enough for this purpose.

I know what the link is about and it is EXACTLY what you asked about.

So...you aren't relating this to Newton's second law?

 

[fascinated]

NASA uses Newton's Law of Gravity to navigate spacecraft and if it's good enough for them, it is good enough for this purpose.

I'm looking for something deeper... sorry., but thanks for the interest and help.

So...you aren't relating this to Newton's second law?

Read the entire link. It teaches the 2nd law to teachers, lol.

 

[sophiecentaur]

The Earth's mass is curving spacetime and everything must follow that line?

I'm looking for something deeper.

from what you have written so far it appears that you may be trying to 'run before you can walk'. You may have read something about and beyond Newtonian Physics but that doesn't imply that you can use terms like "curving spacetime" in a valid way.
If you are telling us that you can do all the (Classical) calculations for a shot at a Moon orbit then I take it all back . . . . .

 

[russ_watters]

I'm looking for something deeper... sorry., but thanks for the interest and help.Read the entire link. It teaches the 2nd law to teachers, lol.

This thread is closed due to your lack of effort. Please feel free to PM me with a sincere and significant attempt to learn and communicate and I will consider re-opening it. If you're interested in that sort of thing.