Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: phases of moon, earth-sun system



Hi-
You can take this demo one step further by thoughtful positioning
of your light source, ball, and observer. The Greeks measured the
distance to the sun by noting when the moon was at exactly 1/2 lit, and
measuring the angle between the lines of sight to the sun and moon. They
knew the lunar distance from parallax (I wouldn't call that
"triangulation" I don't think), in units of the earth's radius.
Their number for the solar distance was not too good, as I recall,
because the relevant angle is so close to pi/2.
Regards,
Jack

Howdy,

I thought the original measurement of the Earth-Moon distance (in
units of the diameter of the Earth - know from Egyptian measurements)
used the fact that the cone of the Earth's Dark Shadow would have a
base of the Earth's Diameter and an opening angle of about 1/2 degree
(the angular size of the Sun at the Earth) and determining, the the
time of the Moon's entry till its exit from that Shadow in a Total
Lunar Eclipse gave the size of the Moon (also a 1/2 Degree angular
size from the Earth) was approximately 3/8 the diameter of the
Earth's Shadow at that distance. That is a Unique Distance.

Good Luck,
--
Herb Schulz
(herbs@interaccess.com)