NavList:

ThomasK
Your 15thSep23.33.  One of us is certainly confused. I’m not sure if it’s you, me, or both of us.  Never mind; I think I’m beginning to get it.  I suspect two things. 

1.  You are using a smart phone.  I prefer a PC with twin 23” monitors, plus a reporter’s pad when I’m too lazy to type or use PowerPoint to draw diagrams.  With a full keyboard, I find it much easier to define the abbreviations I use as I go along.  Also using Shift on a keyboard is less of a pain printing capitals when necessary than with a smart phone.

2.  You’re using a Celestial App, which is programmed to work using decimals of a degree rather than degrees and minutes.  Why do I suspect this?  Looking at your 15^th Sep23.33 post, 25 decimal 55 degrees + decimal 48 degrees = 26 decimal 03 degrees, whereas 25 degrees 55 minutes + 48 minutes of arc = 26 degrees 43 minutes of arc.  I think this must be the problem.  If not come back to me.  .  I did spot one error in my Nautical Almanac example.  Did you spot it?  I subtracted -2’ atmospheric refraction as I would if using the Air Almanac.  In fact, as far as I can see the Moon Correction Table in the Nautical Almanac includes refraction, so that -2’ wasn’t needed.  This would give me ‘Plot 3nm towards’ which is the same as my Air Almanac figure.  I wondered where that 2’ had got to.


Re: taking an upper and a lower limb shot with a bubble, forget it.  Just slap that big yellow moon bang in the middle of your bubble as best you can and take the reading in degrees and minutes of arc; apply index error; and apply P in A from the rear of the Nautical Almanac.  To get P in A, find the first correction from the upper table; find the second correction from the lower table averaging the LL and UL figures in the table; and subtract 15’, because the tables are calculated for LL and you’ve shot the Moon’s centre.  Tonight will be the ideal night to give it a try.

Yes, holding a bubble sextant steady needs a firm hand.  Unfortunately, we’re not all like the Captain Marvel/Marlborough County figures appearing in WW2 sextant company adverts.  You need a bit of help.  British MkIX bubble sextants had a little curly pig’s tail hook on the top of the sextant and another in the top of the astrodome, but at home you can simply sit your sextant on a window ledge and level it up with playing card shims.  You end up on your knees, but so did Christopher Robin.  Now you know why Air Navigators tend to avoid the Moon unless they’re really trying to impress.  DaveP Message Ends.