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mean equator
Hi,
Im reading about satellite navigation and there is a term which i cannot find a definition for- "mean equator" this seems to be defined at a certain year. My giuess is that the mean equator defines the inclination of the sun's apparent elliptic path around the celestial equator. ??? any help is appreciated. Regards, Adam |
#2
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mean equator
Adam Chapman writes: Hi, Im reading about satellite navigation and there is a term which i cannot find a definition for- "mean equator" this seems to be defined at a certain year. My giuess is that the mean equator defines the inclination of the sun's apparent elliptic path around the celestial equator. The earth's rotation axis (and equator) gradually change with time. Some of that change is a constant drift, known as precession. The earth equator and equinox given by precession alone is known as the mean equator and mean equinox. Superimposed on precession is a set of wobbles at different periods, known as nutation. If both nutation and precession have been accounted for, then the corresponding equator and equinox are known as the "true" equator and "true" equinox. The Astronomical Almanac would have more information about this topic. Good luck! Craig |
#3
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mean equator
In article .com,
Adam Chapman wrote: Hi, Im reading about satellite navigation and there is a term which i cannot find a definition for- "mean equator" The "mean equator" is the orientation the Earth's equator would have if the nutation was averaged out. The orientation of the equator with nutation effects included is called the "true equator". Where the equatorial plane of the Earth intersects the celestial sphere, that's where we have the celestial equator. this seems to be defined at a certain year. It's defined at a particular *moment*, not over a whole year. Those moments are usually selected near the beginning of some selected year, e.g. 2000.0 My giuess is that the mean equator defines the inclination of the sun's apparent elliptic path around the celestial equator. ??? any help is appreciated. Regards, Adam -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
#4
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mean equator
thanks everyone |
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