SUBSOLAR AND SUBLUNAR POINTS DEFINITIONS

Posted by E.D.G. October 11, 2008

Questions:

Are the terms "subsolar point" and "sublunar point" official astronomical
terms?

Or are they simply terms that people are using because they are convenient?

A number of researchers including myself are working on an earthquake
research project where we need to be able to determine the latitude and
longitude of several points on the surface of the earth.

If you draw a line connecting the center of the earth and the center of the
sun, then we are referring to the location where that line crosses the
surface of the earth as the "subsolar point."

Similarly, if you draw a line connecting the center of the earth and the
center of the moon, then we are referring to the location where that line
crosses the surface of the earth as the "sublunar point."

Those are convenient and relatively easily understood terms. And if there
is no official policy regarding their use that conflicts with those
definitions then we will continue using them for that.

The reason for making this inquiry has to do with the development of some
computer programs for generating solar system types of data for use with the
earthquake research effort.

One of the programs being developed inputs a time and date. And it
generates latitude and longitude data for those subsolar and sublunar points
for that time.

It generates data for the distances between the earth and the sun, and the
earth and the moon for that time.

And it generates data for what we are calling the "Gravity Point." This is
the location on the surface of the earth where the combined gravitational
pulls of the sun and the moon are strongest for that time. Because the moon
gravity felt here on earth is several times as strong as the sun gravity the
location of the Gravity Point is always within about 25 degrees in any
direction of the sublunar point.

Several earthquake related computer programs like that one are being
developed. The present plan is that when that particular program latitude
and longitude data generation program is in its final form it will be stored
at some Web site as a downloadable freeware .exe program.

We could not find a freeware program that generated those types of numbers.
So we wrote one of our own.