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

Emre Sevinc <emres@xxxxxxxxxxxx> wrote in

> "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T:net@xxxxxxxxxx> writes:
>> Dear Emre Sevinc:
>> "Emre Sevinc" <emres@xxxxxxxxxxxx> wrote in message
>> news:87oe6zmprn.fsf@xxxxxxxxxxxxxxxxxx
>>> 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

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.