# Thread: Will Earths Orbit collapse?

1. As far as I understand our orbit around the Sun is infinite (within bounds of course) because there is no friction to slow it down
firstly if someone could explain in more detail how that works that would be great because even removing all forces bar gravity I don't see how the earth doesn't slowly spiral closer unless there is another force holding the earth out

But I'm just going to go with what I know that the earth goes round the sun infinitely because of a lack of friction etc
however there IS other forces, other planets, celestial objects however far away exhibit at least a miniscule gravitational pull.
therefore because there is a constant tug from the rest of the universe, given enough time (I mean supposing the sun and universe continued existing for eternity) would the earths orbit be affected and send us spiraling into or away from the sun?

PLEASE don't just quote my post and tear it apart telling me how I'm wrong/stupid/don't know what I'm talking about/putting No, Wrong, No after each line etc, If you are that sort of a person (and you know who you are) sod off, your not welcome on my threads
constructive critisism is fine but I'm looking for answers, not people to insult me

2.

3. Originally Posted by Booms
As far as I understand our orbit around the Sun is infinite (within bounds of course) because there is no friction to slow it down
firstly if someone could explain in more detail how that works that would be great because even removing all forces bar gravity I don't see how the earth doesn't slowly spiral closer unless there is another force holding the earth out

But I'm just going to go with what I know that the earth goes round the sun infinitely because of a lack of friction etc
however there IS other forces, other planets, celestial objects however far away exhibit at least a miniscule gravitational pull.
therefore because there is a constant tug from the rest of the universe, given enough time (I mean supposing the sun and universe continued existing for eternity) would the earths orbit be affected and send us spiraling into or away from the sun?

PLEASE don't just quote my post and tear it apart telling me how I'm wrong/stupid/don't know what I'm talking about/putting No, Wrong, No after each line etc, If you are that sort of a person (and you know who you are) sod off, your not welcome on my threads
constructive critisism is fine but I'm looking for answers, not people to insult me
If you consider the earth and sun as an isolated system then the orbit just keeps on keeping on. No friction, or outside forces. Pretty boring.

But as you noted, there are other planets and other bodies in the universe and they all have and associated gravitational field. That means that an exact description of the motion of the sun and the planets requires a coupled solution of the laws of motion that considers the gravitational effect of everything.

If you simply consider the solar system as a closed system, a very accurate approximation, then the motion of the planets is a bit more complicated than the simple model provided by elliptical Keplerian orbits. It requires a solution of the "many body problem" of mechanics. Unfortunately there are no simple closed-form solutions except for the 2-body problem. So one has the question as to whether the planetary orbits are stable.

We don't know if the planetary orbits are stable. It is known from detailed simulations that they do not exhibit wild instability over a period of many thousands of years. But we don't know if they remain stable indefinitely long.

4. off-topic post removed.

5. don't know about infinitely, but its been going for 4 billion years at least and don't see why it won't for another 4 billion, Infinite is a long time to go. I'm not worried in my lifetime, check back with me in 4 billion years.

6. To add to what DrRocket said, the Sun itself is not "stable". It is losing mass as it burns its fuel, which tends to cause planets to move outward, but when it expands into a red giant it will engulf at least Mercury, and its atmosphere might expand out far enough to cause significant drag on Earth even if it is not engulfed.

Again, we are talking loooong time scales.

7. Also, to clarify one point, if you're imagining just the Earth and the Sun in a very simple, closed system, gravity will be the only force. In this case, it can be shown that there are perfectly stable paths for the Earth to follow. So, it is at least theoretically possible that the orbit is stable and the Earth will neither spiral inward nor outward. Of course, as has been mentioned, that's ignoring a lot of other details.

8. Originally Posted by Booms
firstly if someone could explain in more detail how that works that would be great
Newtons's First Law of Motion (based upon extensive observation and brilliant insight and the work of many predecessors): A body will continue in a state of rest or uniform motion unless acted upon by an external force.

9. Originally Posted by John Galt
Originally Posted by Booms
firstly if someone could explain in more detail how that works that would be great
Newtons's First Law of Motion (based upon extensive observation and brilliant insight and the work of many predecessors): A body will continue in a state of rest or uniform motion unless acted upon by an external force.
Yes.

In the case of an orbiting body the force of gravity acts continuously and that is what creates the orbit instead of a straight-line trajectory. Planets do not exhibit uniform motion in the sense of Newton.

The second law F=dp/dt whcih reduces to F=ma for constant mass is more useful in this case.

10. Originally Posted by Janus
To add to what DrRocket said, the Sun itself is not "stable". It is losing mass as it burns its fuel, which tends to cause planets to move outward,
so then the planets are getting energy from the sun, that does affect its orbit?

Yes/No

what is that energy?

Is it affecting us NOW?

can you show the counteraction of gravity and the "forces" adding energy to the planets?

i would like to see the pub sharing the planets moving outward?

but when it expands into a red giant it will engulf at least Mercury, and its atmosphere might expand out far enough to cause significant drag on Earth even if it is not engulfed.
is that speculation?

yes/no

Again, we are talking loooong time scales.[/quote]

Originally Posted by Janus
To add to what DrRocket said, the Sun itself is not "stable". It is losing mass as it burns its fuel, which tends to cause planets to move outward,
so then the planets are getting energy from the sun, that does affect its orbit?

Yes/No

what is that energy?

Is it affecting us NOW?

can you show the counteraction of gravity and the "forces" adding energy to the planets?

i would like to see the pub sharing the planets moving outward?

but when it expands into a red giant it will engulf at least Mercury, and its atmosphere might expand out far enough to cause significant drag on Earth even if it is not engulfed.
is that speculation?

yes/no

Again, we are talking loooong time scales.
[/quote]

The energy transfer from the sun is in the form of radiation, But there is a compensating re-radiation of energy from the Earth to the cosmos. The two are nearly in balance.

It is generally quite save fo neglect radiation pressure in calculating orbits with a few exceptions, Thos exceptions are not generally planets.

12. Originally Posted by DrRocket
Originally Posted by Janus
To add to what DrRocket said, the Sun itself is not "stable". It is losing mass as it burns its fuel, which tends to cause planets to move outward,
so then the planets are getting energy from the sun, that does affect its orbit?

Yes/No

what is that energy?

Is it affecting us NOW?

can you show the counteraction of gravity and the "forces" adding energy to the planets?

i would like to see the pub sharing the planets moving outward?

but when it expands into a red giant it will engulf at least Mercury, and its atmosphere might expand out far enough to cause significant drag on Earth even if it is not engulfed.
is that speculation?

yes/no

Again, we are talking loooong time scales.
The energy transfer from the sun is in the form of radiation,
perhaps light and ionized (particles/atoms) mass? (genesis mission)
But there is a compensating re-radiation of energy from the Earth to the cosmos. The two are nearly in balance.
'nearly'.....?

what about the earth capturing lots of 'greenhouse' heat and it is being retained?

What's that all about, does the 'cosmos' have something to say about what the earth and planets are capturing? (do you have the physics behind that?)

How about all that mass we capture (solar flares, auroras)?

Meaning; can you share why the planets orbits would expand per the question asked of Janus (as you imposed too)?

It is generally quite save fo neglect radiation pressure in calculating orbits with a few exceptions, Thos exceptions are not generally planets.
radiation pressure? do you mean the solar wind? with all that mass and coronal ejections, i am wondering if any of that is being addressed when calculating the expanding orbits?

can you provide something to assist?

i am interested as well to see your 'radiation pressure' when describing orbits and why it is of no consequence, especially when janus suggests the orbits will change based on 'something' (i guess that stuff you don't observe)?

13. the reason the planets are moving outward is to compensate for the sun's slightly lesser mass, per Janus's post. The speeds that the planets have are still relatively constant, it's just that you have to move a bit further out to maintain an orbit instead of either spiraling out of control into the sun or shooting off into the depths of space.

Correct me if I'm wrong please, but the reasoning behind Janus's statement goes along with the equations for and about Centripetal force, the force that keeps our planet and the others in orbit, no? This si because as you increase the radius slightly, you decrease the angular velocity proportionally which will decrease the centripetal force proportionally to the square of the angular velocity.

14. what about the earth capturing lots of 'greenhouse' heat and it is being retained?
That is part of what he is talking about.

What's that all about, does the 'cosmos' have something to say about what the earth and planets are capturing? (do you have the physics behind that?)
No idea what you are getting this from. When you heat something, it gives off heat at a certain rate. The rate at which it happens determines how hot it will get while you are applying heat. Some of the light hitting the earth is reflected right back into space, while some of it gets absorbed and released as IR.

How about all that mass we capture (solar flares, auroras)?
That is a very, very small amount of mass compared to the mass of the earth. A negligible amount.

Meaning; can you share why the planets orbits would expand per the question asked of Janus (as you imposed too)?
The sun loses mass as it "burns' fuel and radiates it away in the form of light and plasma. And before you ask: if you imagine the inside of a ball with a radius of 1AU, then the earth represents a minuscule dot on this surface. That dot represents the percentage of mass that the sun loses that eventually gets absorbed by the earth. A very small amount and insignificant.

radiation pressure? do you mean the solar wind? with all that mass and coronal ejections, i am wondering if any of that is being addressed when calculating the expanding orbits?
Light imparts momentum to a surface that it hits, despite being massless. This pressure is also pretty much negligible though on the scale of the earth.

How about all that mass we capture (solar flares, auroras)?
Density of the Solar wind at Earth orbit distance: 9.6e-21 kg/m³
Velocity of Solar wind: 700 km/sec

If you calculate out the amount of orbital energy the Earth gains from the Solar wind over 1 billion years, it works out to enough to "push" the Earth less than 400 km further from the Sun. On top of that this calculation ignores the drag passing through the solar wind puts on the Earth which tends to reduce orbital energy.

16. Originally Posted by Arcane_Mathematician
the reason the planets are moving outward is to compensate for the sun's slightly lesser mass, per Janus's post.
what about the mass it gains over the same period (ie... is the gravity bringing "stuff' in from space?)

is there physics comparing what mass is gained and lost before that claim is made?

Correct me if I'm wrong please, but the reasoning behind Janus's statement goes along with the equations for and about Centripetal force, the force that keeps our planet and the others in orbit, no? This si because as you increase the radius slightly, you decrease the angular velocity proportionally which will decrease the centripetal force proportionally to the square of the angular velocity.
One minute, it is gravity, the next it is string tension that keeps an orbit

but here is the physics for that http://hyperphysics.phy-astr.gsu.edu/Hbase/cf.html

What i wish each to see and realize is that 'force' is ficticious and does not exist in an inertial frame (kind of screwed with Einstein too) (ie... that would mean you forgot newtons 'preferred frame of reference')

i suggest any to see centrifical and coriolis

ie..... thanks for the post but sorry 'wrong answer'

17. Originally Posted by Janus
How about all that mass we capture (solar flares, auroras)?
Density of the Solar wind at Earth orbit distance: 9.6e-21 kg/m³
Velocity of Solar wind: 700 km/sec

If you calculate out the amount of orbital energy the Earth gains from the Solar wind over 1 billion years, it works out to enough to "push" the Earth less than 400 km further from the Sun. On top of that this calculation ignores the drag passing through the solar wind puts on the Earth which tends to reduce orbital energy.

so to you the solar wind is both giving and dragging?

cool

SO let me get this straight, you are claiming the sun is reducing its mass and that is why you claimed the earths orbit is moving out?

So then if the earth is moving away from the sun, when the sun starts to burn itself out, there should have been enough loss to give us a good orbit for when the sun becomes a red giant?

so in scope, we shouldn't EVER fall into the sun................ is this correct?

Originally Posted by Janus
How about all that mass we capture (solar flares, auroras)?
Density of the Solar wind at Earth orbit distance: 9.6e-21 kg/m³
Velocity of Solar wind: 700 km/sec

If you calculate out the amount of orbital energy the Earth gains from the Solar wind over 1 billion years, it works out to enough to "push" the Earth less than 400 km further from the Sun. On top of that this calculation ignores the drag passing through the solar wind puts on the Earth which tends to reduce orbital energy.

so to you the solar wind is both giving and dragging?
Yes. There are two components to consider, that due to the Solar wind blowing out from the Sun, and that due to the Earth's orbital motion. As a result, the Solar wind from the Earth' perspective does not come directily out from the Sun but from an slight angle. So while at tyhe same time it pushes outward on the Earth, it retards its orbital velocity which cancels out in part the outward push.

SO let me get this straight, you are claiming the sun is reducing its mass and that is why you claimed the earths orbit is moving out?
In the long term, yes. in the short term it is not as simple. For example, during the time interval of 1800 AD-2050 AD, the Earth, on average, increases its distance from the Sun, but during the interval of 3000 BC - 3000 AD, it, on average, decreases it disance from the Sun.

So then if the earth is moving away from the sun, when the sun starts to burn itself out, there should have been enough loss to give us a good orbit for when the sun becomes a red giant?

so in scope, we shouldn't EVER fall into the sun................ is this correct?
That remains to be seen. It depends on a number of factors:

How large will the Sun get.
How much mass does the Sun lose between now and then.

And as I pointed out in my earlier post, even if the Earth escapes being swallowed by the expanding Sun in the intial expansion, it still could be close enough for there to be significant enough drag caused by the Solar atmosphere to casue it to spiral back in to the Sun.

Originally Posted by Arcane_Mathematician
the reason the planets are moving outward is to compensate for the sun's slightly lesser mass, per Janus's post.
what about the mass it gains over the same period (ie... is the gravity bringing "stuff' in from space?)

is there physics comparing what mass is gained and lost before that claim is made?
The mass that the Sun is gaining? It's rather insubstantial compared to the amount of mass ejected through solar flares and the amount of mass lost to energy through the nuclear processes in the sun. Bishadi, you have no knowledge of legitimate physics, and are in no position to say I'm wrong. I'd prefer one of the more experienced members who are trained in the field to delegate whether or not I understand the processes involved.

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