A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2017 Sep 24, 08:18 -0700
Excellent reply Robin,
Yes, you need to take in account both :
- Most northern star to be always above the Horizon . If you want a clear view of it, let's define that its height should always be above 10° (but it could somewhat be lower of course in clean and clear air) hence the Observer should always be south of N17° in order to see Gacrux with 10° minimum elevation as a circumpolar star around the South Pole. And :
- Sun to be always below the horizon at midnight local solar time, let's say for instance at 9.5 ° minimum below the horizon. If we assume the Sun southernmost Declination to be S 23.5°, then you would like the Observer to be at least 33° away from the south Pole, which tells you that the Observer should remain north of 57 ° South.
Hence, with some solid safety net, you can state that between S57° and N17° an observer can sight the Southern Cross at night with naked eyes any time during the year. If we accept shrinking this safety net, then the S57°-N17° strip can be widened of course, up to maybe S62°-N22° but probably not much more. We could refine this a bit through checking the Azimuth of the Southern Cross at Midnight local solar time at or around Dec 21 st.
Nonetheless, this is why our Ozeee and Kiwi Friends - among them you Bruce - can always enjoy this spectacular constellation all year round.
I had never though about that until I flew for months in a row to Islas Malvinas / Falkland Islands ( @ 57° S as I can remember) 2 years ago when they were still searching and spot drilling for oil there. Whatever the season I could always spot Lady Southern Cross from the air during the night.