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Bruce H, you wrote:
"Fix by Occultations of the moon and stars. Well that certainly got my
attention, Please post more. I assume that something similar to lunar
calculations are used, but the distance is almost zero."

Sure. That's one way to do it. Historically, this was used as a method of 
determining GMT and thus longitude.

We can get a fix from a pair of occultations the same way that we can get a 
fix from a pair of lunar distances. Imagine shutting off all the stars in the 
universe (including the Sun) except two. They send their feeble glow across 
the lightyears and faintly illuminate the Earth. As the Moon orbits around, 
it casts a shadow through space from each of the stars. That shadow is a 
cylinder of effectively infinite length as far as observers on Earth are 
concerned. If the Earth passes through the shadow, then as seen from the 
Moon, there is a darnk circular shadow on the Earth exactly matching the 
profile of the Moon, nearly circular with the same diameter as the Moon, but 
with some hills and valleys around the margin. Any small section of the edge 
of this intersection between the cylinder and the Earth is a line of position 
which we can use just like any other line of position. So if we're on Earth 
and we see one of those two lonely stars wink out a known instant of GMT, we 
can plot, after some calculation, an LOP for that observation. If we wait a 
few minutes or hours (even days) and the Moon eclipses that second star, then 
we get a second LOP which we can cross with the earlier one, advanced if 
necessary, and that will give us a true fix. This method can be quite 
accurate if the Moon's limb is correctly modeled and the occultations are 
carefully timed.

Let's imagine a practical case. You're on a little Antarctic adventure. Maybe 
you're going to be to cross Antarctica on skis during Antarctic night for the 
"Save the Penguins" charity. You've specifically chosen to eschew GPS and you 
are navigating mostly by dead reckoning. You have an accurate watch set to 
GMT. You're dragging yourself across the ice sheet when you come upon a 
large, well-preserved meteorite. There are lots of these up there, but this 
one is a beauty and you want to get back here. You don't have a sextant, but 
you do have a spotting scope so you'll use occultations for a fix. Lucky you, 
there's a faint star just a few minutes of arc ahead of the Moon's dark limb 
and and another about a degree and a half beyond that. So you wait for the 
first star to be occulted and note the GMT as exactly as possible. Then you 
sit around for three hours enjoying a meal of delicious roast penguin (we 
won't tell the charity about that). You time the second occultation and 
record it. Then back on the skis and off we go. Months later, back in a warm 
climate, you fire up your occultation analysis software, identify those two 
faint stars by eyeball, and work out two lines of position. They cross at 
your meteorite.

-FER


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