when will our planet stop rotating?

i heard that the earth rotation is slowly slowing down. we have longer
days now than during the roman era. i heard this is due to friction
between earth and whatever.
so when will the earth stop rotating completely?
when it reaches almost that stage, will we have a day that takes as
long as a year or more?
will life still exist with one side constantly baked by the sun while
the other side completely remains dark? would you want to live on the
bright side or the dark side?

(meat n potatoes) writes:

i heard that the earth rotation is slowly slowing down. we have longer
days now than during the roman era. i heard this is due to friction
between earth and whatever.

Tidal interaction with the Moon.

so when will the earth stop rotating completely?

It won't. Once tidal evolution has completed, the Earth will
rotate with the same period as the Moon's orbit.

[rec.arts.movies.current-films taken out of newsgroups list; follow-ups
also restricted]

meat n potatoes wrote:
i heard that the earth rotation is slowly slowing down. we have longer
days now than during the roman era. i heard this is due to friction
between earth and whatever.
so when will the earth stop rotating completely?
when it reaches almost that stage, will we have a day that takes as
long as a year or more?
will life still exist with one side constantly baked by the sun while
the other side completely remains dark? would you want to live on the
bright side or the dark side?

The Earth's rotation is slowing down, due to a tidal interaction with
the Moon. Roughly speaking, the Moon raises two high tides on the
Earth--one on the side facing the Moon, and one on the other side.
If the Moon revolved around the Earth once per day, those high tides
would remain in the same place on the Earth. But the Moon does not
revolve that fast; instead, it revolves around the Earth about once
every 28 days, with respect to the stars.

As a result, the Earth, which does rotate once per day, is rotating
"under the tides," so to speak. We who are bound to the Earth by
gravity usually think of the high tides coming to us (if we live by
the coasts), but it is really we who rotate toward the high tides;
they rotate much slower than the Earth.

Because of this disparity in speeds, the tidal bulges in the oceans
(and to a lesser extent, the land masses) act as a frictional brake
on the Earth's rotation. This brake is not very strong; the Earth's
day lengthens by about 1 second every 60,000 years or so. If you
lived back in the days of the ancient Greeks, for instance, you would
not be able to tell the difference even with a reasonably accurate
wris****ch.

However, the differences add up. Because of this increase in the
length of the day, astronomical events such as eclipses took place
at different times of day and in different locations of the Earth
than they would have if the Earth's rotation rate were constant, and
the distance between where they "ought" to have been and where they
were really recorded tells us how fast the Earth's rotation is slowing
down.

By Newton's third law, incidentally, if the tidal bulges are pulling
back on the Earth's rotation, the Earth's rotation is pulling forward
on the tidal bulges. Those bulges, in consequence, are not directly
under the Moon, but are instead slightly ahead of it. They, in turn,
pull the Moon forward, pushing it into a slightly higher orbit. This
effect, like the slowing of the Earth's rotation, is very small,
amounting to (I think) centimeters per year or so.

However, that too adds up and the current consensus is that the Moon
orbited much closer to the Earth back in the days when it was young,
about 4 billion years ago. Since the strength of the tides varies
inversely as the cube of the distance between the Moon and the Earth,
a Moon that is, say, 5 times closer creates tides that are 125 times
as intense. Imagine the tidal bulges that washed across the land in
*those* days!

As the Earth slows its rotation down, the tidal slowing itself gets
smaller and smaller, since the difference between the Earth's rotation
and that of the tidal bulges is decreasing. To be sure, the revolution
of the Moon also slows down as a result of its receding from the Earth,
but that effect is not large enough to counteract the lengthening of
the day. If the Earth-Moon system were left alone, the day and month
would both lengthen to the point where both lasted about, oh, 40 days
or so. At that point, the Earth and Moon would both be tidally
locked, the tidal bulges would be in sync with the Earth's rotation,
and there would be no further slowdown.

However, the Earth-Moon system is not left alone. In particular,
there is the Sun to concern ourselves with. Through a more complex
interaction, it would act to bring the Earth and Moon, still tidally
locked, back closer together again. I say "would act," because the
time scales on which this would happen are in the tens or hundreds
of billions of years. Long before that happens, the Sun will become
a red giant and possibly swallow the Earth and Moon, making the latter
part of this analysis entirely academic (if it wasn't already). The
Earth and Moon will probably not come close to getting tidally locked
to one another before then.

To answer your other questions, it used to be thought that the Sun
would stay at roughly the same temperature for the rest of its lifetime
as an ordinary star. It now appears that that won't happen--that the
Sun will gradually warm over the next few billion years. Although the
increase will be slow from the perspective of the Sun, it will likely
be enough to raise the surface temperature of the Earth above the
boiling point of water within a billion years or so, and that will be
that for life on the surface. We could consider moving elsewhere at
that time--assuming, of course, that we're still around to consider it.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Wow!!! Now that is a fine answer. Even I learned something.

--

----
Joe S.

"Brian Tung" wrote in message
...
[rec.arts.movies.current-films taken out of newsgroups list; follow-ups
also restricted]

meat n potatoes wrote:
i heard that the earth rotation is slowly slowing down. we have longer
days now than during the roman era. i heard this is due to friction
between earth and whatever.
so when will the earth stop rotating completely?
when it reaches almost that stage, will we have a day that takes as
long as a year or more?
will life still exist with one side constantly baked by the sun while
the other side completely remains dark? would you want to live on the
bright side or the dark side?

The Earth's rotation is slowing down, due to a tidal interaction with
the Moon. Roughly speaking, the Moon raises two high tides on the
Earth--one on the side facing the Moon, and one on the other side.
If the Moon revolved around the Earth once per day, those high tides
would remain in the same place on the Earth. But the Moon does not
revolve that fast; instead, it revolves around the Earth about once
every 28 days, with respect to the stars.

As a result, the Earth, which does rotate once per day, is rotating
"under the tides," so to speak. We who are bound to the Earth by
gravity usually think of the high tides coming to us (if we live by
the coasts), but it is really we who rotate toward the high tides;
they rotate much slower than the Earth.

Because of this disparity in speeds, the tidal bulges in the oceans
(and to a lesser extent, the land masses) act as a frictional brake
on the Earth's rotation. This brake is not very strong; the Earth's
day lengthens by about 1 second every 60,000 years or so. If you
lived back in the days of the ancient Greeks, for instance, you would
not be able to tell the difference even with a reasonably accurate
wris****ch.

However, the differences add up. Because of this increase in the
length of the day, astronomical events such as eclipses took place
at different times of day and in different locations of the Earth
than they would have if the Earth's rotation rate were constant, and
the distance between where they "ought" to have been and where they
were really recorded tells us how fast the Earth's rotation is slowing
down.

By Newton's third law, incidentally, if the tidal bulges are pulling
back on the Earth's rotation, the Earth's rotation is pulling forward
on the tidal bulges. Those bulges, in consequence, are not directly
under the Moon, but are instead slightly ahead of it. They, in turn,
pull the Moon forward, pushing it into a slightly higher orbit. This
effect, like the slowing of the Earth's rotation, is very small,
amounting to (I think) centimeters per year or so.

However, that too adds up and the current consensus is that the Moon
orbited much closer to the Earth back in the days when it was young,
about 4 billion years ago. Since the strength of the tides varies
inversely as the cube of the distance between the Moon and the Earth,
a Moon that is, say, 5 times closer creates tides that are 125 times
as intense. Imagine the tidal bulges that washed across the land in
*those* days!

As the Earth slows its rotation down, the tidal slowing itself gets
smaller and smaller, since the difference between the Earth's rotation
and that of the tidal bulges is decreasing. To be sure, the revolution
of the Moon also slows down as a result of its receding from the Earth,
but that effect is not large enough to counteract the lengthening of
the day. If the Earth-Moon system were left alone, the day and month
would both lengthen to the point where both lasted about, oh, 40 days
or so. At that point, the Earth and Moon would both be tidally
locked, the tidal bulges would be in sync with the Earth's rotation,
and there would be no further slowdown.

However, the Earth-Moon system is not left alone. In particular,
there is the Sun to concern ourselves with. Through a more complex
interaction, it would act to bring the Earth and Moon, still tidally
locked, back closer together again. I say "would act," because the
time scales on which this would happen are in the tens or hundreds
of billions of years. Long before that happens, the Sun will become
a red giant and possibly swallow the Earth and Moon, making the latter
part of this analysis entirely academic (if it wasn't already). The
Earth and Moon will probably not come close to getting tidally locked
to one another before then.

To answer your other questions, it used to be thought that the Sun
would stay at roughly the same temperature for the rest of its lifetime
as an ordinary star. It now appears that that won't happen--that the
Sun will gradually warm over the next few billion years. Although the
increase will be slow from the perspective of the Sun, it will likely
be enough to raise the surface temperature of the Earth above the
boiling point of water within a billion years or so, and that will be
that for life on the surface. We could consider moving elsewhere at
that time--assuming, of course, that we're still around to consider it.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Brian Tung wrote:

snip
To answer your other questions, it used to be thought that the Sun
would stay at roughly the same temperature for the rest of its lifetime
as an ordinary star. It now appears that that won't happen--that the
Sun will gradually warm over the next few billion years. Although the
increase will be slow from the perspective of the Sun, it will likely
be enough to raise the surface temperature of the Earth above the
boiling point of water within a billion years or so, and that will be
that for life on the surface. We could consider moving elsewhere at
that time--assuming, of course, that we're still around to consider it.

Google for "Frank J. Tipler" to see what will happen to us.....



Bill Tallman

wrote:
(meat n potatoes) writes:


i heard that the earth rotation is slowly slowing down. we have longer
days now than during the roman era. i heard this is due to friction
between earth and whatever.


Tidal interaction with the Moon.


so when will the earth stop rotating completely?


It won't. Once tidal evolution has completed, the Earth will
rotate with the same period as the Moon's orbit.



Good answer, just be warned- this guy is a troll named Gaza. Note the
x-posting.

(I kept rec.arts.movies.current-films in on purpose).

In the spirit of On Topic-ness does anyone know what the time frame of
Earth's rotation coming to and end might be and would the sun have nova
ed by then?

In any case humans will either not be here or be both here & elsewhere
so I would tend to think we have more immediate troubles like pollution
to deal with.

And for the movie buffs, check out 'Day After Tomorrow'.

TBerk

wrote in message
...
(meat n potatoes) writes:

i heard that the earth rotation is slowly slowing down. we have longer
days now than during the roman era. i heard this is due to friction
between earth and whatever.

Tidal interaction with the Moon.

so when will the earth stop rotating completely?

It won't. Once tidal evolution has completed, the Earth will
rotate with the same period as the Moon's orbit.

So if people are living on the "wrong" side of the Earth they will never see
the moon?

Brian Tung wrote:

The Earth's rotation is slowing down, due to a tidal interaction with
the Moon. Roughly speaking, the Moon raises two high tides on the
Earth--one on the side facing the Moon, and one on the other side.

I had a physics teacher in college who told me about the time he applied
to a Phd. program. He was interviewed by none other than Edward Teller.
Teller asked him why there are two simultaneous high tides on the earth.
The reason for the high tide on the side facing the moon is obvious but
why is there another high tide on the opposite side? The answer is not
so obvious.

Brian- Let's give the others some time to think about this before you
answer. :-)


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starman wrote:
I had a physics teacher in college who told me about the time he applied
to a Phd. program. He was interviewed by none other than Edward Teller.
Teller asked him why there are two simultaneous high tides on the earth.
The reason for the high tide on the side facing the moon is obvious but
why is there another high tide on the opposite side? The answer is not
so obvious.

Did he get it right?

Brian- Let's give the others some time to think about this before you
answer. :-)

Unfair!

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Brian Tung wrote:

starman wrote:
I had a physics teacher in college who told me about the time he applied
to a Phd. program. He was interviewed by none other than Edward Teller.
Teller asked him why there are two simultaneous high tides on the earth.
The reason for the high tide on the side facing the moon is obvious but
why is there another high tide on the opposite side? The answer is not
so obvious.

Did he get it right?

I don't think he did. I wouldn't be surprised if many BS-physics
graduates didn't know. That's why Teller used it as one of his test
questions for PhD. candidates.

Brian- Let's give the others some time to think about this before you
answer. :-)

Unfair!

The universe is not only unfair, it's indifferent. :-)


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