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The speed of earth's rotation around itself and the sun



 
 
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  #1  
Old September 11th 05, 07:18 PM
Emre Sevinc
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Default The speed of earth's rotation around itself and the sun


I was talking to a friend of mine and this subject
came up: What happened to the speed of earth? Is it
a few milliseconds slower than, say, it had been a few thousand
years ago? We faintly remembered sci. & tech news
we read so I decided to ask:

How does speed of the earth's rotation around itself
change around itself during time? Are we having
longer or shorter days? How is this related to the
speed of earth's rotation around the sun? Are our
years getting longer or shorter? What is the
relationship between a body's rotation around
its axis and the rotation around some other body
such as sun?

I hope some of the physicists here can provide
some URLs or pointers.

Thanks in advance.

--
Emre Sevinc

eMBA Software Developer Actively engaged in:
http:www.bilgi.edu.tr http://ileriseviye.org
http://www.bilgi.edu.tr http://fazlamesai.net
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http://www.cogsci.boun.edu.tr
  #2  
Old September 11th 05, 08:06 PM
N:dlzc D:aol T:com \(dlzc\)
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Dear Emre Sevinc:

"Emre Sevinc" wrote in message
...

I was talking to a friend of mine and this subject
came up: What happened to the speed of earth? Is it
a few milliseconds slower than, say, it had been a few
thousand years ago? We faintly remembered sci. &
tech news we read so I decided to ask:

How does speed of the earth's rotation around itself
change around itself during time?


The Earth is slowing, as angular momentum is transferred from
Earth (spin) to the Earth-Moon system (increase in the orbital
radius of the Moon) via tides.

Are we having
longer or shorter days?


Longer.

How is this related to the
speed of earth's rotation around the sun?


It isn't related, although it may affect how much energy the Sun
can transfer to/from the Earth-Moon system.

Are our
years getting longer or shorter?


You might look at the "tidal rhythmite" data. I think the length
of year is pretty stable... look for references to "recession".

What is the
relationship between a body's rotation around
its axis and the rotation around some other body
such as sun?


It really depends. All sorts of non-correlations right here in
our solar system.

David A. Smith


  #3  
Old September 11th 05, 08:24 PM
Jonathan Silverlight
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In message ze%Ue.228507$E95.159553@fed1read01, "N:dlzc D:aol T:com
(dlzc)" writes
Dear Emre Sevinc:


Are our
years getting longer or shorter?


You might look at the "tidal rhythmite" data. I think the length
of year is pretty stable... look for references to "recession".


I've raised this before, but can't remember the answer! Is there any way
to tell? Rhythmites tell us there were more days in the year than there
are now, but AFAIK that assumes the year is the same length.
--
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  #4  
Old September 11th 05, 08:39 PM
Emre Sevinc
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Default

"N:dlzc D:aol T:com \(dlzc\)" N: dlzc1 D:cox writes:

Dear Emre Sevinc:

"Emre Sevinc" wrote in message
...

I was talking to a friend of mine and this subject
came up: What happened to the speed of earth? Is it
a few milliseconds slower than, say, it had been a few
thousand years ago? We faintly remembered sci. &
tech news we read so I decided to ask:

How does speed of the earth's rotation around itself
change around itself during time?


The Earth is slowing, as angular momentum is transferred from
Earth (spin) to the Earth-Moon system (increase in the orbital
radius of the Moon) via tides.

Are we having
longer or shorter days?


Longer.

How is this related to the
speed of earth's rotation around the sun?


It isn't related, although it may affect how much energy the Sun
can transfer to/from the Earth-Moon system.

Are our
years getting longer or shorter?


You might look at the "tidal rhythmite" data. I think the length
of year is pretty stable... look for references to "recession".



Thanks a lot for the explanation. I'll use the
keywords you have provided for further research.



--
Emre Sevinc

eMBA Software Developer Actively engaged in:
http:www.bilgi.edu.tr http://ileriseviye.org
http://www.bilgi.edu.tr http://fazlamesai.net
Cognitive Science Student http://cazci.com
http://www.cogsci.boun.edu.tr
  #5  
Old September 12th 05, 12:27 AM
Llanzlan Klazmon
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Default

Emre Sevinc wrote in
:

"N:dlzc D:aol T:com \(dlzc\)" N: dlzc1 D:cox writes:

Dear Emre Sevinc:

"Emre Sevinc" wrote in message
...

I was talking to a friend of mine and this subject
came up: What happened to the speed of earth? Is it
a few milliseconds slower than, say, it had been a few
thousand years ago? We faintly remembered sci. &
tech news we read so I decided to ask:

How does speed of the earth's rotation around itself
change around itself during time?


The Earth is slowing, as angular momentum is transferred from
Earth (spin) to the Earth-Moon system (increase in the orbital
radius of the Moon) via tides.

Are we having
longer or shorter days?


Longer.

How is this related to the
speed of earth's rotation around the sun?


It isn't related, although it may affect how much energy the Sun
can transfer to/from the Earth-Moon system.

Are our
years getting longer or shorter?


You might look at the "tidal rhythmite" data. I think the length
of year is pretty stable... look for references to "recession".



Thanks a lot for the explanation. I'll use the
keywords you have provided for further research.


Just a curiosity to add to your quest. The Earth's rotation rate measurably
sped up with the recent Indian Ocean earhquake. The rupture of the fault
caused a large enough change in the Earth's moment of inertia to result in
a detectable shortening of the day. In general though, the trend is for the
days to slowly length as angular momemtum gets transferred to the moon's
orbit.

As far as changes to the period of the Earth's orbit around the Sun, well I
don't know how we could tell that prior to the invention of sufficiently
accurate clocks. I would say that if what we know of gravity is correct
then there are no significant purturbing factors to the length of the
Earth's orbit around the Sun although it is known that the eccentricity of
the orbit does slowly change with time as does the apsidal line.

Klazmon.







  #6  
Old September 12th 05, 01:15 AM
N:dlzc D:aol T:com \(dlzc\)
external usenet poster
 
Posts: n/a
Default

Dear Johnathan Silverlight:

"Jonathan Silverlight"
wrote in message
...
In message ze%Ue.228507$E95.159553@fed1read01, "N:dlzc D:aol
T:com (dlzc)" writes
Dear Emre Sevinc:


Are our
years getting longer or shorter?


You might look at the "tidal rhythmite" data. I think the
length
of year is pretty stable... look for references to "recession".


I've raised this before, but can't remember the answer! Is
there any way to tell? Rhythmites tell us there were more days
in the year than there are now, but AFAIK that assumes the year
is the same length.


Rhythmites assume a constant infall of matter to produce the
layers? So much accumulated debris = so much time. The
distribution/nature of the debris describes the day, month, and
annual cycles. I can't say I remember either.

David A. Smith


  #7  
Old September 12th 05, 03:21 AM
N:dlzc D:aol T:com \(dlzc\)
external usenet poster
 
Posts: n/a
Default

Dear Llanzlan Klazmon:

"Llanzlan Klazmon" wrote in message
.6...
....
Just a curiosity to add to your quest. The Earth's rotation
rate
measurably sped up with the recent Indian Ocean earhquake.
The rupture of the fault caused a large enough change in the
Earth's moment of inertia to result in a detectable shortening
of the day.


Do you have a citation for this? The only references I have seen
is that this purported decrease in length of day was a
*prediction*. A prediction which apparently ignored the fact
that amorphous rock is *less* dense than the magma it floats on,
which subduction displaces more dense stuff to higher "altitude",
increasing the moment of inertia, which should *slow* the Earth's
rotation.

David A. Smith


  #8  
Old September 12th 05, 10:53 PM
Steve Willner
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Default

[Change in length of year.]

In article ,
Jonathan Silverlight writes:
Is there any way to tell?


I don't think there are any direct measurements. It's possible to
_calculate_ the Earth's and other planets' orbits. I think I recall
seeing calculations for 10^9 years or so, but a quick check finds
only 10^8. Touma and Wisdom (1994 AJ 108, 1943) calculated the
Earth-Moon orbit characteristics for 10^9 years. I don't see how
they could do that without knowing what all the other planets were
doing over that time, but I haven't read their paper in detail.

Maybe someone else will track this down. You could start with an ADS
abstract search on J. Wisdom.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
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  #9  
Old September 13th 05, 07:27 PM
Paul Hirose
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Default

According to this page at the U.S. Naval Observatory, the Earth's
rotation is about 1.4 milliseconds slower per day per century.

http://tycho.usno.navy.mil/leapsec.html

--
Paul Hirose
To reply by email remove INVALID

 




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