Difference between revisions of "Sub-Earth Point"
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==Description== | ==Description== | ||
| − | The '''sub-Earth point''' is the location on the surface of the Moon where a particular point on the Earth is directly overhead. It can be found by drawing an imaginary line from the center of the Moon to the center of that point on the Earth. It is normally described by giving the [ | + | The '''sub-Earth point''' is the location on the surface of the Moon where a particular point on the Earth is directly overhead. It can be found by drawing an imaginary line from the center of the Moon to the center of that point on the Earth. It is normally described by giving the [[selenographic%20coordinates|selenographic]] longitude and latitude of that point.<br /> <br /> |
==Additional Information== | ==Additional Information== | ||
* If not otherwise specified, the '''sub-Earth point''' would normally be assumed to be referenced to the center of the Earth. However, it is almost invariably meant to mean the location of the sub-Earth point for an observer at a specific location on the Earth's surface -- something that is more properly referred to as the '''Sub-Observer Point'''. | * If not otherwise specified, the '''sub-Earth point''' would normally be assumed to be referenced to the center of the Earth. However, it is almost invariably meant to mean the location of the sub-Earth point for an observer at a specific location on the Earth's surface -- something that is more properly referred to as the '''Sub-Observer Point'''. | ||
| − | * The numeric values of the longitude and latitude of the Sub-Earth point are the same as the quantities referred to as the [ | + | * The numeric values of the longitude and latitude of the Sub-Earth point are the same as the quantities referred to as the [[librations|librations]]. If computed for an imaginary observer at the Earth's center, the result is the '''geocenric librations'''. If computed for a specific observer on (or above) the surface, the result is the '''topocentric librations'''. |
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Latest revision as of 17:54, 15 April 2018
Contents
Sub-Earth Point
(glossary entry)Description
The sub-Earth point is the location on the surface of the Moon where a particular point on the Earth is directly overhead. It can be found by drawing an imaginary line from the center of the Moon to the center of that point on the Earth. It is normally described by giving the selenographic longitude and latitude of that point.
Additional Information
- If not otherwise specified, the sub-Earth point would normally be assumed to be referenced to the center of the Earth. However, it is almost invariably meant to mean the location of the sub-Earth point for an observer at a specific location on the Earth's surface -- something that is more properly referred to as the Sub-Observer Point.
- The numeric values of the longitude and latitude of the Sub-Earth point are the same as the quantities referred to as the librations. If computed for an imaginary observer at the Earth's center, the result is the geocenric librations. If computed for a specific observer on (or above) the surface, the result is the topocentric librations.
LPOD Articles
Bibliography
