NavList:

Bruce,

As you were thinking out loud,

"Just thinking further about this...... Until this problem, I never really noticed that the altitude correction table was really two tables, 10-90 and 0-10 degrees. I never thought about it because I read somewhere it is "bad" practice to measure altitudes less than 20 degrees or so. We had good results with a time sight at sunset- a negative angle. Also, I've had good results with LOPs measuring altitudes of 12- 15 *. This begs the question.... For reasonable results of +/- 7 NM, what is the smallest sun sight altitude that can be measured with a good horizon? Must be using an ordinary sextant, not one that measures to 10 seconds!"

I would sub divide low altitude observations into ultra low altitudes ( below 3*) and low altitudes (3* to 10*). The ultra low observations are more susceptible to abnormal refraction from weather and differences between water and air temperatures. Low altitude observations will give satisfactory results if the body of choice can be seen through the haze or low clouds. If you can see it then you can shoot it. I would worry more about horizon quality rather than how low to the horizon a body is. Certainly any body above 10* will get it done.

"What if you are an explorer at 66* north this time of year? No noon sight? Depend on stars? Just thinking aloud!"

In addition to stars there is the Moon some of the time and planets most of the time available to the high latitude navigator.

Greg Rudzinski

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