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RE: Sidreal Time????

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Posted by Kip Crawford on May 15, 2000 05:33:58 UTC

Sidreal time and real time are basically related. However sidreal time deals in another matter of measurement. Every hour of time the Earth turns 15 degrees. 24 hours times 15 degrees equals 360 degrees. Right Asension (RA) is measured in hours minutes and seconds. In general sky surveying, everything is measured in arc-seconds and arc-minutes. The moon is 30 arc-minutes wide (sidreal time)or 1800 arc-seconds or 7.5 degrees. The "arc" basically is the sky`s travel. The sky isn`t flat it`s arched. 29 arc-seconds is very small amount of time and you never notice it with the naked eye. 90 arc-minutes is an substantial amount of movement, but it is (1.5 real hours) and (22.5 degrees sidreal time). There`s many books that explain how it is done. It really isn`t hard. I may have not explained well, but real time is just time elapsed whereas sidreal time is a measurment of celectial distance traveled in real time.

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