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If you have socks to wash or anything even mildly interesting to do,
skip this message.

A landmark event occured today. I took my first real sight.

I have a Davis Mark 15 that I took out of the box for the first time
a few weeks ago. I twiddled with the mirrors here and there and then
broke down and read the rest of the manual and got them back where
they should be. I'm too far from the sea, so I looked on the web for
artificial horizon stories, and found this mailing list. It's been
raining for the last week. Then today, the cloud cover broke about
15:00.

I was on my way home and noted the sunshine. I rushed in and got a
saucer of water and put it in the second story window. The sun was
heading toward the roofs, and I knew I didn't have long.

By the time I got half situated with note pad and sextant, the
shadow had crept onto the window sill. I moved the plate to a sunny
spot on the coffee table. I flipped a few filters down, set the arc
to 0 and brought the sun down to the coffee table. I shimmied left
and right, I rotated the sextant, I turned the micro-drum. My heart
was beating faster. Is this good enough? Is it really "resting
lightly" on the horizon/image? Am I doing this right? MARK. I looked
at my watch, analog, and jotted some numbers. 15:02:55. 36 23.8

I had a dark spot in my vision, which can't be good. Need more
filters. Flip, flip. I got the now-blue sun on my saucer of water
and turned the micro-drum, remembering to come up from the below the
horizon/image, the same way every time. Am I lined up right? Which
image is the reflection? MARK. 15:05:05. 35 41

Man that sun is fast, and the shadow was starting to crowd me off
the coffee table. Ah ha. I lept to the west window and threw open
the heavy drapes to a flood of sunshine on the dining room table.
Saucer on table, I adjust the index arm and line up again. Time,
time, time! MARK 15:06:50. 35 4.2

I see how this works now. Take your time. Breath. Get the images
lined up on each other and them move the reflection up. Slowly.
Slowly. MARK. 16:08:25. 34 31.4

One more for five. MARK. 16:09:55. 33 55.6

Now, what was that index error thing? Oh, right. How do you do that
with an artificial horizon? I don't know. So I took a try at some
far off object. It was -5' (off the arc?).

I remembered something about a graph to fish good sights from the
garbage, but I didn't have any graph paper (or so I thought). So, I
look at the differences in time and see if the differences in sights
is proportionally similar. Too much math. By some convoluted
contortions of my pea brain, I decided that reading #4 was the best
of the bunch. I used my car's GPS to give me a larger-than-life DR
position.

After two and a half hours fumbling with the forms in the Complete
On-Board Celestial Navigator (2003-2007 edition), I had a number: 7'
(Towards) az. 236.

Good thing I wasn't on a boat somewhere and really needed to know.

Given the accuracy of my DR, I expect I can get closer, and maybe my
IE was not too accurate, but heck for a first shot, it was close
enough for me.

Your prize for reading this far? Questions from a newbie.

How do I use the different colored filters? The orange one seems
good for cloudy days. The blue for bright days? Do you use them all
at once?

Is there a slick way to check index error with an artificial horizon?

Thanks.

Paul Flint
Kawasaki, Japan

   

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