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Author
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Topic: Star finder for sun bearings
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David Burch
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posted November 14, 2004 06:34 PM
This question was sent by email and moved here:
Regarding Starfinder on page 103 of Emergency Navigation book. Is the followig correct. If I live at 45N then use that template. Pick the sunrise direction and zero declination on the template and mark anywhere on the white disk. Also mark this on the rim scale with time. Then every 15 degrees is another hour and the direction and declination will be correct as the day progresses.
From: Starpath, Seattle, WA
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David Burch
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posted November 14, 2004 06:36 PM
Yes that is essentially correct, but the terminology may be off some. Yes every 15° is one hour for just about any application, but we cannot really read declination from it. The idea of p 103 is that you must first
1) compute or look up somehow the numerical bearing of sunrise from your latitude and date. example today nov 14, 2004 at lat 45.00 north bearing to sunrise is 115.5 (get this various ways, i just computed it with the starpilot, using lon = 0.0)
2) put on the right template for that lat in this case 45 N. rotate till the blue arrow is at 000 (it does not matter where we put this but it is easir to count hours if we start at 000)
3) reach under and place mark along Hc = 0° rim of the template at Zn = 115.5. ( my usual way of doing this is to lift the template edge holding it in place, make a first guess as best i can, relax the template back down to flat then see how i need to adjust, ie 1 mm "NW of my mark" is correct)
3) Now that is the sun and it is rising (crossing the Hc = 0 line) at the right time and you can follow its bearing and height throughout the day... use rise time = T (it is actually 06 56 36 at lon 0) you should find LAN at 11 44 37 with Hc = 26° 37' and setting at 1631 54 at bearing 244.4. all of these relative times at 15° per hour along the rim of the white plate.
From: Starpath, Seattle, WA
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