Re: Commercial Flight Sunset
From: Gary LaPook
Date: 2016 May 16, 23:50 -0700
Sight reduction for this image with Hs upper limb Sun at 0° worked out well on my Palm Pilot calculator but manual tabular methods proved troublesome. There were issues with the order of corrections and what to do about refraction for a large negative Ho altitude. Has anyone else tried correcting this observed 0° Hs from a 12788 foot (3875 M) height of eye ? The Palm Pilot Navigator used - 56' as the refraction correction vs. - 34' if from sea level. I am assuming temp. press. corrections would be as if at sea level.
I have attached a scrap of paper that has been in my wallet for 35 years.
First apply dip of 110'.
Then apply refraction from the attached correction table from the Air Almanac. At 10,000 feet the refraction for a zero sextant altitude shot is -50' and from 15,000 feet it is -55' so take your pick.
Then apply SD of -16'.
So Ho = 110'
-181' or - 3° 01'. But since the refraction correction table is only printed in 5' intervals it would be silly to carry that 01' so call the Ho - 3° even.
Note that the refraction is less at altitude due to the thinner layer of air above the airplane compared to sea level. Also note there is a temperature correction feature to the refraction correction table for large temp differences that you could apply if you knew the temp at your altiude.