Re: Earth's dimensions

oriel36 <kelleher.gerald@xxxxxxxxx> wrote in
news:50c5a936-959d-4680-8cdc-bd1d19f56450@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:

The Earth's Equatorial circumference is 40,075 km which yields 111.32
km per geographical degree and 1669.8 km per 15 degrees -

http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/tables/
t
able02.html

At the Equator there is a rapid transition from daylight to darkness
as the Earth turns at 111.32 km every 4 minutes/1 degree while at 60
degrees latitude there is a longer transition to darkness (twilight)
as the Earth turns a slower 55.80 km every 4 minutes/1 degree.

As the Earth turns 1669.8 degrees for 15 degrees/1 hour of rotation,it
is remarkable to see an alternative 1674.4 km value given for rotation
in 1 hour -

"Want to do the calculation for yourself? The circumference of the
Earth at the equator is 40,075 km. And the length of time the Earth
takes to complete one full turn on its axis is 23.93 hours. So
40,075/23.93 = 1,675 km"

http://www.universetoday.com/guide-to-space/earth/how-fast-does-the-
ear
th-rotate/

If 15 degrees of geography and rotation yielded 1675 km then the total
Equatorial circumference would be a nonsensical 40200 km or 125 km in
excess of the actual 40,075 km value.No offence to the ee guys but
geologists are stuck with one of the worse breaches of reasoning which
has its roots in the late 17th century which makes it impossible to
work with planetary dynamics or even global geography and geology.




I know it is an exercise in futility to introduce reality into this
conversation, but:


You seem to forget that the earth orbits the sun, and that the
tangential velocity due to the earth's rotation needs must be calculated
from an external, non-rotating frame of reference. Such a reference
frame is provided by the stars. I'm sure you will have observed that
through the course of a year the sun appears to move against the
background of the distant stars at roughly 1 degree per day as a
consequence of the earth orbiting the sun. Thus, using the average time
from consecutive meridian transits of the sun to calculate the speed of
the earth's rotation will be in error, since the earth needs to turn
just a little less than 361 degrees between successive 'noons' in order
to account for the yearly travel of the sun. If you repeat your
calculations accurate to six significant figures, you will discover that
in one 24 hour period a point on the earth's equator will travel
40,184.7 km, or just a hair shy of 361 degrees. This is exactly how far
it needs to travel to get the sun from one meridian transit to another,
considering that the sun is moving eastward against the background of
distant stars at 0.98 degrees per day (on average - it varies because of
the eccentricity of Earth's orbit and resulting variation in orbital
velocity).
.

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