darell
Cruiser
Posts 27
Points 27
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i've just gone through some navigation techniques. i worry that i must be completely missing out on something, since this technique occurred to me:
Picture this:
1. The sky is clear for measurements
2. You have a good quality watch set to GMT
For longitude, is it possible to:
1. Take sun sightings to find the exact local noon, when sun is at it's zenith
2. Find exact timezone difference between position and Greenwich
3. Translate that to degrees to get your longitude
could this work?
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yes, indeed! it's possible to take sightings to find the exact local noon.
this technique includes sightings before local apparent noon or LAN, then recording the time and the sextant reading (hs).
then you can proceed with the noon sight for latitude as normal. and immediately reset your sextant to the reading taken before LAN, and wait for descent of the sun. in your sextant, it just kisses the horizon you recorded the exact time.
and to give you the exact time of the sun's crossing on the meridian, you then add the two twice and divide by two again.
After that, search for the sun's GHA in an almanac for the time you calculated and that is your longitude.
plain and efficient. If you do it carefully, you can reach the few miles of your longitude, which is good enough for a ships sailing on high seas.
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There's this really good book called Longitude, that goes through the process and politics of developing a reliable method on how to compute longitude as you sail. try to research on that.
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