The sun has a large apparent disc covering a big area. The lower limb has more atmospheric refractive bending than the upper limb. By the way, the bent light makes it look high, just like shooting at a fish with an arrow. With the lower limb appearing a bigger percentage higher than the upper limb, it makes the sun look flattened as it approaches the horizon.

So how have others been adjusting for the centerline of the apparent disc? Somewhere  between the upper limb and lower limb tabulated amounts, but not exactly half way which would not allow for the increased effect on the lower limb?

Heck, I'm not even sure how to figure the halfway point, which would at least be fairly close to correct. I added the two corrections, one is a negative number so I got a smaller negative number. Appears sensible but seems awfully easy, so I fear it may be wrong.

Anyone have any ideas or good/bad experiences?

Edit: I should have mentioned that I'm using a reflective artificial horizon.

We've just added the procedure for carrying out a Sun sight reduction while using the horizon. 

It is thorough with step-by-step instructions and plenty of pictures and examples. 

A Sun sight reduction form is included which is used in the described process.

The procedure also includes the plotting of the LOP.

This is perfect for the beginner who is having difficulty understanding how to carry out a Sun sight reduction, what documents are needed, where to get them.


Complete Sun Sight Reduction Procedure



CelNav57

We've just added the procedure for carrying out a Sun sight reduction while using the horizon. 

It is thorough with step-by-step instructions and plenty of pictures and examples. 

A Sun sight reduction form is included which is used in the described process.

The procedure also includes the plotting of the LOP.

This is perfect for the beginner who is having difficulty understanding how to carry out a Sun sight reduction, what documents are needed, where to get them.


Complete Sun Sight Reduction Procedure


CelNav57

Why is the print so small on both Pub. 249 and HO-229?

All of the print in sextant work is small.

I tell you I'm going blind!!!

Roland

To my surprise I got no new astro-nav equipment for Christmas. 

The Seahorse hardcase I asked for didn't come down the chimney!

Nuts.

Here is something I remembered that may or may not be helpful.

When I was about ten years old I purchased a very cheap plastic sextant. I could never understand the "grownup" directions that came with it.

One evening I was standing facing the western horizon trying to aim at the horizon and pick up a star in the mirror. A cool Coast Guard guy came by and told me "Try doing it this way". He had his own "real" sextant that seemed to weigh 100 pounds. He showed me that if I held the sextant upside down and pointed the telescope at the star, it was easy to find the horizon in the mirror, couldn't miss.

OK, maybe everyone knows this, or maybe I remember it wrong, but that is the way I remember it. I'm old now so that was long ago.

For some reason I'm reading about celestial navigation and interested in learning the basics. Finally, after all this time! I've always navigated the mountains and wilderness using stars and moon and sun as a compass for direction only, but especially not for longitude. In the north, Polaris always shows your basic latitude with no tables or books. But longitude is difficult.

How do you all note the time to the second when operating alone? Glance at watch and subtract a second, then read the angle?

This doesn't directly have much to do with the process of sun sights but it's a small portion of a video about Alain Kalita sailing solo non-stop around the world.


Here's a portion of the video while he's taking a sun sight.  The sun sight's at the 5:37 mark.

I'm lazy and sometimes am not inclined to work with paper-and-pencil so I use this spreadsheet;

Sunsight reduction spreadsheet

I put the program on my cheapy tablet and get Ho, Hc, Zn and Int. fast.

It can be used to determine any needed figures for the Sun.

Such as;

-Sunrise (UTC)

-Sunset
-MP

Very handy.

Lou

The far left hand column of the Moon Altitude Correction Tables has App. Alt. in it.  Do I assume correctly that the column is for minutes of Ha?

Altitude Correction Tables for the Moon

Confused,

Paul

Sextant - David Barrie

This one line made the whole read worthwhile.

"It is time to rediscover the joys of celestial navigation, not merely as a safety net, but because using a sextant to find our way puts us in the closest possible touch with the natural world at its most sublime. "


We use the universe to find our place in it.