These original Kirt's Cogitations™
may be reproduced (no more than 5, please) provided proper credit is given to me, Kirt
– noun: Concerted thought or reflection; meditation; contemplation.
Kirt [kert] – proper noun: RF Cafe webmaster.
Obliquity of the Equinoxes
The Tropic of Cancer
and the Tropic of Capricorn are defined as the 23.5° north and south
latitudes, respectively, because Earth's 23.5° axis tilt means those
are the points where the sun is directly overhead at the vernal and
autumnal equinoxes, respectively. At least that is what early observations
determined. In reality, gravitational perturbations caused by the sun,
planets, asteroids and other minor objects causes the axis tilt to vary
between 22.1° and 24.5° during a cycle of about 41,000 years. Current
obliquity is decreasing by just under 0.4 arc seconds per year. This
effect can account for a solar heating variation of about +/-1% for
the +/-1° of tilt. Far larger climate effects are caused by the long-term
variations (due to the same forces) in the eccentricity of Earth's orbit,
which can vary between 0.0005 (almost circular) to 0.0607 (currently
0.0160) over a period of about 10,000 years. Keep this in mind when
reading the next report on global warming; remember in that in the 1960s,
and 1970s, the environmental "experts" were in a tizzy over what they
were certain was a coming ice age, and were given prime print space
in major publications like Fortune, Time, and Newsweek.