Studying Celestial "d" corrections

[gjordan]

I must disagree about leaving the moon alone. It is one of the more useful bodies because for about a third of the month you can get an actual fix in the daytime, rather than just an LOP. It is a little more complicated than stars but certainly not black magic. It is also handy (daytime or dusk) for the aging eyes, since it is much brighter than stars or planets. I went from sun and stars to planets and moon in the first week of my first passage using the Ketteridge book. I had printed up 150 copies of the work sheet and by the end of the passage could work out problems on the back of a napkin. And again, I advise NOT to learn to do a noon sight because you are likely to get complacent and not go any farther. A noon sight is also very difficult if the sun is near your latitude and you are trying to shoot something almost directly overhead. Just another opinion based on about 15,000 miles before I bought a GPS. I got lazy after that. _____Grant.

[Mike1956]

Dear All,

I thought I would like to apologise for confusing the thread, I take full responsibility. All part of the learning process I guess. However as a result of my posting I am pleased to say I feel I have captured the piece of the jigsaw I had missing re the d corrections.

Thanks All.

I was also going to enquire why I should leave the Moon alone forever. Surely if the thing was of no use they would not publish the data for it in the almanac?

However Grant has already addressed this issue.

Mike

[nigel1]

Originally Posted by gjordan

I must disagree about leaving the moon alone. It is one of the more useful bodies because for about a third of the month you can get an actual fix in the daytime, rather than just an LOP. It is a little more complicated than stars but certainly not black magic. It is also handy (daytime or dusk) for the aging eyes, since it is much brighter than stars or planets. I went from sun and stars to planets and moon in the first week of my first passage using the Ketteridge book. I had printed up 150 copies of the work sheet and by the end of the passage could work out problems on the back of a napkin. And again, I advise NOT to learn to do a noon sight because you are likely to get complacent and not go any farther. A noon sight is also very difficult if the sun is near your latitude and you are trying to shoot something almost directly overhead. Just another opinion based on about 15,000 miles before I bought a GPS. I got lazy after that. _____Grant.

With a decent star telescope, Venus is observable during daylight. An inspection of the almanac will show if there is enough angular speration between Venus and the sun to make a decent fix. Would need to pre-work Venus to get the rough altitude to set on the sextant to make it easier to find.

As for high altitude sun shots, I like them, take a sight a few minutes before mer pass, and a second sight a few minutes after. The suns position can be plotted directly on the chart (convert GHA to longitude), then use the true zenith distance as the radius of a position circle. Position circles can be drawn on the chart. There will be two cross points, but you should have a good idea of which is the correct one.

[El Pinguino]

Originally Posted by Mike1956

Dear All,

I thought I would like to apologise for confusing the thread, I take full responsibility. All part of the learning process I guess. However as a result of my posting I am pleased to say I feel I have captured the piece of the jigsaw I had missing re the d corrections.

Thanks All.

I was also going to enquire why I should leave the Moon alone forever. Surely if the thing was of no use they would not publish the data for it in the almanac?

However Grant has already addressed this issue.

Mike

That was said marginally tongue in cheek.... the reason most avoid the moon is the added complexity of the corrections . That is why I suggest that makee-learnees avoid it until they have mastered the simpler stuff such as 'd' corrections for the sun

The simplest way to utilise Venus is when it is on the meridian.... easy to find, easy to take, easy to reduce. Combined with the sun at the same time yields a good fix as opposed to the more common sun-run-sun which is of course just a simple running fix.