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View Full Version : Earth's orbit around the sun is slowing down??



maxima128
2004-Jan-02, 03:57 AM
Is Earth's orbit around the sun is slowing down? Yes, according to a Jan. 1, 2004 article in CNN.COM's Science & Space section (http://www.cnn.com/2004/TECH/science/01/01/leap.second.ap/index.html).

The CNN article's headline refers to the slowing down of Earth's rate of spin which we've compensated for since 1972 by adding a leap second at the end of each year. But strangely enough, since 1999, the earth's rotational spin has not slowed as scientists expected, leaving them quite confused. Interesting.

But later, the CNN article states "the Earth's orbit around the sun has been gradually slowing for millennia". I'm no astronomer, but I think this is probably a mistake. People always seem to confuse the rotation of the earth with its revolutions around the sun.

But now I wonder: is it possible for earth's orbit to slow or speed up? If so, what could cause it? Throughout its existence, has the earth's orbital speed ever changed?

If the earth's orbital speed was somehow slowed down, I presume the sun's gravity would gradually pull the earth closer and closer to the sun until we burned up. But if the opposite happened and the earth's orbit was speeded up, would we eventually drift off into space in increasingly larger orbits? Or would the earth find a new permanant orbit that was compatible with its new speed?

frenat
2004-Jan-02, 01:49 PM
I believe and I'm sure others will be along later to correct me if I'm wrong that like the moon, the earth is not only slowing down in its orbit but also getting farther away thus still keeping the orbit stable. The cause for this is friction from tidal forces.

maxima128
2004-Jan-02, 05:20 PM
So tidal forces are slowing down the earth's orbit around the sun and also causing it to move away from the sun? I guess this means our years are also getting increasingly longer.

milli360
2004-Jan-02, 06:59 PM
The changes in the Earth's year are minute (eh) compared with the changes that that article is talking about.

Although, it is difficult to tell exactly what they are talking about because they seem to get so much confused.

They claim that scientists added a leap second on the last day of the year for 28 years. Leap seconds were not added every year, and sometimes they are added in June.

They say that the Earth orbit around the sun (the year) has been slowing for millennia, but a NIST spokesman says they have no explanation why it (the day) is on schedule. Regardless of the confusion, the situation is more complex. We've talked about this a few times before (http://www.badastronomy.com/phpBB/viewtopic.php?p=3934#3934). The day is not just on schedule, it has sped up.

The NIST page (http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm) gives a list of leap seconds, and when they were added. And they note that there was not one in December. Unless something drastic happens, another leap second won't be added until June, if then.

PS: I see we have another thread on the same article: Earth on Time? (http://www.badastronomy.com/phpBB/viewtopic.php?t=10184&start=0)

Sticks
2004-Jan-05, 01:08 PM
Pardon my pedentry here, but as all orbiting bodies travel in elipses aka Kepler's laws, the planets will speed up as it approaches the sun and slows down as it goes away

This is so that a planet sweeps out an arc of equal areas in equal time

Or am I missing something

tracer
2004-Jan-05, 10:01 PM
Sticks: You are correct. The Earth is indeed moving faster at perihelion (closest approach to the sun) than it is at aphelion (farthest distance from the sun).

However, the article in question dealt with (or at least brushed up against) the change in duration of an entire orbit. The acceleration from aphelion to perihelion, and the deceleration from perihelion to the next aphelion, happen within the course of a single orbit and are accounted for.

amstrad
2004-Jan-06, 04:55 PM
Pardon my pedentry here...

Not to be pedantic, but the word is spelled "pedantry." ;)

Sticks
2004-Jan-06, 06:04 PM
Not to be pedantic, but the word is spelled "pedantry." ;)

:oops:

Sorry, but I was at the dentist yesterday and was still phased by the injection I had to have to get a broken piece of tooth out. :(

tracer
2004-Jan-06, 09:59 PM
Sorry, but I was at the dentist yesterday and was still phased by the injection
Not to be pedantic, but the word you're looking for is "fazed".

(God, I'm evil! ;) )

twixter
2009-Jan-23, 08:16 PM
Okay, please correct me if I am wrong.

The tidal stresses exerted by the moon on the Earth are slowing down the Earth's rotation, or at least they should be, according to known Physics. The orbital period of the Moon around the Earth is also slowly increasing over time due to these same tidal stresses. This means the moon is slowly moving away from the Earth.

The Sun also exerts tidal stresses on the Earth, affecting the tides, and as a result the Earth's orbital period is also increasing, so the Earth is slowly moving away from the Sun.

So, two questions.

What is happening to the ratio of days per year? Is it increasing, decreasing, staying the same, or we can't tell which? My guess is that since the tidal effect of the Moon is much greater, and its mass is much less than the Sun, the changes to the Lunar orbit and the Earth's rotation are greater than the rate of change for the Earth's Solar orbit. So, I suspect there will be fewer days per year in the distant future.

Also, will there eventually be no more total Solar eclipses seen from Earth? My understanding is that some solar eclipses, then the Moon is near apogee, are already annular, meaning the Moon cannot completely cover the sun. Since the Moon is getting smaller more quickly than the Sun is, there will be a final total eclipse many thousands or millions of years from now, lasting a bare fraction of a second, maybe on some mountaintop. Has anyone calculated how long from now that event should be? I suppose that by then, if we are still around, we might have the means to keep the Moon close to us.

The last post was over 5 years ago, so I don't expect a reply. How permanent is the Internet, I wonder. Will someone read this millenia from now? What a horrifying thought.

Doodler
2009-Jan-23, 08:50 PM
Not to be pedantic, but the word you're looking for is "fazed".

(God, I'm evil! ;) )


Oh lawdy be...Miss Gillian has backup.. :lol:

Ilya
2009-Jan-23, 09:18 PM
[FONT=Georgia]So, two questions.

What is happening to the ratio of days per year? Is it increasing, decreasing, staying the same, or we can't tell which? My guess is that since the tidal effect of the Moon is much greater, and its mass is much less than the Sun, the changes to the Lunar orbit and the Earth's rotation are greater than the rate of change for the Earth's Solar orbit. So, I suspect there will be fewer days per year in the distant future.

I am fairly certain you are correct, but have no math to prove it.


Also, will there eventually be no more total Solar eclipses seen from Earth? My understanding is that some solar eclipses, then the Moon is near apogee, are already annular, meaning the Moon cannot completely cover the sun. Since the Moon is getting smaller more quickly than the Sun is, there will be a final total eclipse many thousands or millions of years from now, lasting a bare fraction of a second, maybe on some mountaintop. Has anyone calculated how long from now that event should be?
IIRC, total solar eclipses will be a memory in about 400 million years. I don't think it can be calculated much more precisely than that, as there are too many factors involved.

Nowhere Man
2009-Jan-24, 05:46 AM
Thread necromancy alert! Five years this time.

(Ah, I see that twixter noticed that) Welcome to the board, twixter.

Fred

NEOWatcher
2009-Jan-27, 03:00 PM
Thread necromancy alert! Five years this time.
(Ah, I see that twixter noticed that)...
Yeah, but I'm not sure Doodler noticed.


Oh lawdy be...Miss Gillian has backup.. :lol:
Considering that was before Miss Gillian joined, I think it might be the other way around. ;)


Welcome to the board, twixter.
Ditto.

Fazor
2009-Jan-27, 11:42 PM
Not to be pedantic, but the word you're looking for is "fazed".

Wha? Did someone call for me? I'm confused. :)