OT: Earth's orbit changing?

[Baron Munchausen]

Well, yes, the pole does shift around slowly all of the time. There was a news story Last year about the north magentic pole heading off into the Arctic Ocean (it has been in northern Canada in historic times) and they think it will go all the way to Russia.

http://www.cnn.com/2002/TECH/space/03/20/north.pole/

You can see a nice map of its drift during the time its location has been known at this page:

http://science.nasa.gov/headlines/y2...neticfield.htm

But the 'reversal' is something completely different than the usual drift. It's probably true that we won't see this flip occur in our lifetimes and that is all that 'really matters' for the pedestrian sort of person who doesn't read SciFi and speculate for themselves all the time like we 4X gamers do.

[Fyron]

Originally posted by JurijD:
Yes but you're forgetting the fact that the universe won't be expanding forever... it will prolly collapse back in again or slow expaing when the distances between particles become so great that the forces of gravity and whatever this force is that is pushing galaxies apart become equal.

Maybe. You can not say for certain what is going to happen to the universe... There is nothing approaching consensus on what the fate of the universe will be. You can not say for certain that the universe will not be expanding forever. I suppose that if you want to get really picky I can add a qualifier of "while the universe is not shrinking" to my earlier statement. The problem is that evidence seems to indicate that the rate at which the galaxies are drifting apart is increasing, not decreasing.

[Lexicon]

To return to the origional topic:

The earth's orbit slowing down is part of the earth-moon-sun orbital system and conservation of angular momentum (Jupiter also has an influence). The short of it is, because of this dynamic, the earth moves slightly away from the sun over time which causes its orbit to slow down. This is a good thing, due to the fact that the sun is slowly heating up over time.

The longer explanation is that the tidal forces between the earth and the moon slow down the earths rotation which reduces its angular momentum, but angular momentum must be conserved so the earth moves farther from the sun (creating a longer angular arm). Moving away from the sun means the earth's orbit must slow down to remain stable (but not as much as the angular arm increases angular momentum).

Makes sense?

[Cipher7071]

Good point, Lexicon. That is a steady influence that must be accounted for. But the original question involved what could cause a change of one second per year. It does not seem that tidal forces alone would cause a change of that magnitude. Yet, the discussion is beginning to accumulate a number of other, more transient things that may also be factors.

[ January 09, 2004, 15:18: Message edited by: Cipher7071 ]

[Spoo]

the earth moves slightly away from the sun over time which causes its orbit to slow down

But increasing the distance between the earth and the sun would would make earth orbit faster. Recall Kepler's third law, period^2 = distance^3.

[Lexicon]

Originally posted by Spoo:
But increasing the distance between the earth and the sun would would make earth orbit faster. Recall Kepler's third law, period^2 = distance^3.

You got the law right but the relationship wrong. Period is the inverse of speed. Therefore a longer period means a slower moving body. (Though it isn't really that simple due to the fact that an increased distence means a longer circumference of the orbit.)

[ January 09, 2004, 21:24: Message edited by: Lexicon ]

[Lexicon]

In case you want the details:

period = t
circumference = L
speed = velocity = v

t^2 = d^3
L = 2(Pi)d
vt = L

Therefore vd^(3/2) = 2(Pi)d yielding v = 2(Pi)/d^(1/2) or speed equals twice pi divided by the square root of distance.

[ January 09, 2004, 21:58: Message edited by: Lexicon ]

[Baron Munchausen]

Dunno if this has any direct relevance to Earth's orbit or magnetic field, but the stuff swirling around under our feet appears to be getting more active. Yellowstone National Park is one big caldera, a 'supervolcano' and it is getting more active in the Last few years.

http://www.bbc.co.uk/science/horizon...olcanoes.shtml

And btw, after some Googling I think the issue is rotational speed, not orbital speed. I couldn't find anything about earth's orbit changing, and I don't think we can measure that accurately enough to notice 1 second's difference. But I did find articles about changes in Earth's rotation and how they have oddly noticed that some years they need a 'leap second' and other years they don't.

http://en2.wikipedia.org/wiki/Leap_second

http://www.astronomy.com/Content/Dyn...1/617efgfc.asp

http://www.astronomy.com/Content/Dyn...1/617efgfc.asp

[Suicide Junkie]

The longer explanation is that the tidal forces between the earth and the moon slow down the earths rotation which reduces its angular momentum, but angular momentum must be conserved so the earth moves farther from the sun (creating a longer angular arm). Moving away from the sun means the earth's orbit must slow down to remain stable (but not as much as the angular arm increases angular momentum).

The tidal forces between the earth and moon have no effect on our distance from the sun.

It does cause the moon to spiral outwards and the Earth's rotation (length of day/night) to slow, though.

The tides induced by the sun are a smaller effect, and those forces are exerted on a much heavier body...
If I recall the spin directions correctly, the solar tides would tend to push the earth in an outward spiral...

[Suicide Junkie]

And btw, after some Googling I think the issue is rotational speed, not orbital speed. I couldn't find anything about earth's orbit changing, and I don't think we can measure that accurately enough to notice 1 second's difference.

Since the year is almost 360 days, a difference of one day would translate to a shift of about 1 degree in the star field.
Similarily, a shift of one second, would cause the starfield background to shift by one 24th of a second of arc (1/3600th of a degree)
Google tells me that a 150mm telescope has a resolution limit of about 0.9 seconds of arc.
Larger research scopes would of course be better.

So, if the orbital period of Earth was off by a second, you should see a shift in the starfield relative to the sun, of about one arc-second.

[ January 09, 2004, 23:26: Message edited by: Suicide Junkie ]