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    Re: Star sight planning with star charts
    From: David Pike
    Date: 2022 Dec 9, 01:46 -0800

    David McN

    The US Air Almanac (but not the UK one), available free online, will give you star diagrams for two hourly intervals and 25-degree latitude intervals throughout the entire year.  HO249/AP3270 Vol1, also available free online, will give you height and azimuth of a varying choice of seven selected stars for 0-360 degrees of LHA Aries and every latitude from 89S to 89N.  I.e., your assumed position will need to be a whole number of degrees of lattude and your assumed longitude will have to be chosen to give you a whole number of degrees of LHA Aries.  But beware, if buying used from eBay, you need the correct ‘epoch’ (ten-year date spread), because SHA changes due to p&n.  Alternatively, you can buy an online programme like ‘Navigator’ for a few £s/$s which, amongst other things, will generate you a sky diagram for any time and place for years into the present, past, and future.  Alternatively, you could use the free online application ‘Stellarium’, which is excellent, but which I find tends to offer too much for my small brain to cope with.  Any will help you choose the best near 120 or 90 degree cuts. 

    Just using SHAs to predict azimuth cuts probably doesn’t always work, because SHA is measured along the celestial equator and azimuth is measured around your own horizon.  Frank will correct me if I’m wrong, but if you were at the Earth’s equator, the celestial equator would start in the east, pass over your head, and disappear to the west, so all stars on the celestial equator would have azimuth 090 or 270 irrespective of their SHA. Got to lie down now; my head hurts. DaveP

    DaveP

       
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