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review_of_astronomical_coordinates [2016/11/17 00:02] adam |
review_of_astronomical_coordinates [2019/07/30 09:55] davner removed |
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+ | ===== Hour Angle, Declination ===== | ||
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+ | On the celestial sphere Hour Angle (HA) is the angle from the local meridian measured along the Celestial Equator (CE) to a given point on the sphere at a particular right ascension (great circle that runs through the north and south celestial poles). Thus the meridian is zero with positive values being west of it and negative to the East. Since the subtended angle comes about by the rotation of the Earth the sexagesimal expression is the number of hours, minutes and seconds that the given point will/did cross the meridian. In this sense positive values of HA indicate the time that has elapsed since the passage through the meridian and negative values indicate the time remaining for the passage to occur. Declination is of course the measured angle north/south from the Celestial Equator. | ||
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+ | Since this is a local coordinate system defined by location on the Earth, the meridian has an HA value of 0 and equal to the line of Right Ascension along which it (currently) outlines. This line of Right Ascension (RA) is the Local Sidereal Time (LST). Thus HA = LST - RA . Note that when the HA is 0... then RA = LST . This is useful for engineering purposes. Many telescope GUIs show LST in their heads up display. If you want to point the telescope to the meridian at a given declination simply input the LST value. For the Schulman telescope the [[understanding_schulman_telescope_limits|park position]] has coordinates of (LST,-32). The [[using_the_lcogt_gui_and_moving_the_telescope|LCOGT GUI]] allows switching between coordinate systems. " | ||
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+ | An attempt was made to show two arbitrary stars at an HA of 2. The limitations of the author' | ||
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