OT: Earth's orbit changing?

[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...