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Subsolar and Sublunar Points definitions Oct. 11, 2008



 
 
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  #1  
Old October 13th 08, 09:22 AM posted to sci.astro
E.D.G.
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Default Subsolar and Sublunar Points definitions Oct. 11, 2008

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.
  #2  
Old October 13th 08, 10:14 AM posted to sci.astro
Paul Schlyter[_2_]
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Default Subsolar and Sublunar Points definitions Oct. 11, 2008

In article ,
E.D.G. wrote:
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.


There is no "official" definition of these words which conflicts with
your use. I don't think there's any "official" definition at all for
these words. After all, these words are pretty self-explanatory.


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.


That point is always very near the point where the Sun can be seen in
your local zenith.

Because the moon
gravity felt here on earth is several times as strong as the sun gravity the


No, it's not!

The Sun is some 390 times as distant as the Moon.

The Sun's mass is some 330 000 Earth masses, while the Moon's mass is
about 1/81 Earth mass. Which implies that the Sun's mass is some
27 million lunar masses.

The force of gravity is proportional to the mass, and inversely proportional
to the square of the distance. Which implies that the gravity from the
Sun upon the Earth is 27 million / 390 ^ 2 = approximately 180 times
stronger than the gravity from the Moon upon the Earth.

You're probably thinking of the tidal forces rather than the gravitational
forces. The tidal forces are inversely proportional to the cube of the
distance, which means the tidal force from the Sun is some
27 million / 390 ^ 3 = approximately 0.45 times the tidal force from
the Moon.

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.



--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stjarnhimlen dot se
WWW: http://stjarnhimlen.se/
  #3  
Old October 13th 08, 11:33 PM posted to sci.astro
Dr J R Stockton[_1_]
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Posts: 426
Default Subsolar and Sublunar Points definitions Oct. 11, 2008

In sci.astro message , Mon, 13 Oct 2008
09:14:14, Paul Schlyter posted:
In article ,
E.D.G. wrote:


There is no "official" definition of these words which conflicts with
your use. I don't think there's any "official" definition at all for
these words. After all, these words are pretty self-explanatory.


Try the OED; that has weighty authority.

Chambers, which is sound, has just that meaning for subsolar; and
broader but compatible ones for sublunar. The headers indicate that the
questioner is distributed over UK academia; so no need to consider
anything Webster might assert. Wikipedia confirms "subsolar".


Because the moon
gravity felt here on earth is several times as strong as the sun gravity the


No, it's not!


...


You're probably thinking of the tidal forces rather than the gravitational
forces. The tidal forces are inversely proportional to the cube of the
distance, which means the tidal force from the Sun is some
27 million / 390 ^ 3 = approximately 0.45 times the tidal force from
the Moon.


OTOH, the inverse square fields are in effect felt by the Earth as a
whole, and it moves accordingly; so it is the tidal fields which are
*felt* at the Earth's surface.


ASIDE : If you're ever passing the Lebanese Embassy, you could ask why a
part of one of my Web pages is in the source of two of theirs -
discovered by using 'Live search' on 'javascript merlyn' - example
http://www.lebanonembassy.se/. My E-mail bounced. They seem to be
fairly near you, just short of Karlaplan!

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
  #4  
Old October 18th 08, 01:04 AM posted to sci.astro
E.D.G.
external usenet poster
 
Posts: 22
Default Subsolar and Sublunar Points definitions Oct. 11, 2008

"Paul Schlyter" wrote in message
...
There is no "official" definition of these words which conflicts with
your use. I don't think there's any "official" definition at all for
these words. After all, these words are pretty self-explanatory.


Because the moon
gravity felt here on earth is several times as strong as the sun gravity
the


No, it's not!


You're probably thinking of the tidal forces rather than the gravitational
forces. The tidal forces are inversely proportional to the cube of the
distance, which means the tidal force from the Sun is some
27 million / 390 ^ 3 = approximately 0.45 times the tidal force from
the Moon.


Posted by E.D.G. October 17, 2008

Thanks for those valuable comments. It took several days for the Newsgroup
postings to appear on my Internet server, hence the delayed response.

As there does not appear to be a problem with the use of the terms "subsolar
point" and "sublunar point" we will plan on continuing to use them on an
informal basis.

Regarding the strength of the sun and moon gravities, what you said makes
sense to me. The earth does rotate around the sun and not around the moon
to the same extent.

However, what this means is that I now have to go back and review the
theories on which my earthquake related programs are based. The programs
work. And that means that the equations they are using must be correct.
But those equations are apparently not working for the reasons I thought
they were probably working.

  #5  
Old October 18th 08, 01:10 AM posted to sci.astro
E.D.G.
external usenet poster
 
Posts: 22
Default Subsolar and Sublunar Points definitions Oct. 11, 2008

"Dr J R Stockton" wrote in message
nvalid...

Posted by E.D.G. October 17, 2008

Thanks for the comments.

As I stated in my other posted response, considering the information in
these posts I am now planning to go back and probably reformulate some of
the theories on which my earthquake related programs are based.

 




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