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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. |
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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/ |
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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. |
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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. |
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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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