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Horizon Over Water  
User currently offlineC-fyow From Canada, joined Feb 2000, 116 posts, RR: 0
Posted (15 years 3 months 3 weeks 5 days ago) and read 1923 times:

I was told a longtime ago, that polots can use their
fist placed in front of them to determine the degrees
close to a sunset over large bodies of water, (oceans)
in case of instrument failure. If this is close to being
correct, can someone enlighten us on this???


2 replies: All unread, jump to last
User currently offlineCdfMXTech From United States of America, joined Jul 2000, 1341 posts, RR: 24
Reply 1, posted (15 years 3 months 3 weeks 2 days 2 hours ago) and read 1861 times:

don't know...but I think it'd be easier just to put the IRUs in ATtitude mode or use the stby horizon indicator!!!

User currently offlineBuff From Australia, joined Mar 2007, 0 posts, RR: 1
Reply 2, posted (15 years 3 months 3 weeks 1 day 21 hours ago) and read 1848 times:

That might work close to the equator, but as you go further north and closer to June 21, it won't work. The "idea" is that if the sun is 15 degrees above the horizon, then it will take one hour for it to set.

Additionally, the higher in altitude you are, the less importance is the geography below you, i.e. ocean or land.

If your question is to determine when "nightfall" is to occur, then perhaps a rough guess would be that a clenched fist at arm's length represents about 15 degrees of declination or one hour. For more precise estimates, one must know one's lat/long and the exact time GMT. A set of sunset tables would make the calculation exact.

Hope that helps,

Best Regards,


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