Next message: Fred Hebard: "Re: Sun squash- was Green Flash and Longitude"
Gentlemen,
The comments on green flash and longitude reminded me of a project I once
undertook to establish longitude from estimating the percent squash of the
sun due to refraction after rising, or before setting. It all started
during a flight I was making in a single-engine Cessna airplane from
Honolulu to Wake Is. In 1973 we had no navigation equipment except a radio
direction finder which told which way to go, but not when you would get
there. Also it could fail. Thus, I always used an aircraft sextant on such
trips. Around noon I actually crossed the subpoint of the sun. Sextant
read 90 deg. no matter which way I looked. This was handy since I could
immediately put a fix on my chart without using the 249 tables. It
otherwise took a long time to work out a sight while flying with my knees,
not having an autopilot. Later as the sun was beginning to set (this was a
15 hour flight), and I was still a few hundred miles out, I planned to grab
a longitude by observing the sunset. All was fine until it did set... on a
cloud deck! So without a real horizon I couldnąt use the sight. But I
remembered that the sun began to show a squash as it approached the clouds.
So I began to think about correlating the percent squash with the actual
altitude, so I could get around this cloud problem. And I thought it may be
of use to people on land too, who had no accurate horizon.
For the next several months I took hundreds of photos of the sun as it was
rising or setting, noting the time and known geographic position. I
projected each photo on the wall of a room, and measured the height and
width of the disk, thus getting the amount of squash. Working backwards
from the almanac refraction tables, I was able to correlate the percent
squash not with just Hs, but directly with Ho. I even developed correction
curves for temperature and pressure (including altitude). As it turned out,
maximum squash ever observed was only about 17%. I tested this method with
my co-workers who while driving to work in the morning would note the squash
and the time. We would work the sight out, and to our surprise, they were
never more than 3 or 4 miles off. For a long time after that, I would note
sun squash while driving cross country, and work the sight upon return, with
the same apparent accuracy.
I had in mind to publish a book on celestial navigation anyway, and the sun
squash chapter could be łthe hook˛, that is, some information that had never
been published before to give it intrinsic value. There would be an insert
with ellipses of 5, 10, and 15 % printed on sun shade material, that could
be held up to compare with the actual sun. Trouble was, I could not produce
such ellipses of suitable quality for publication. I needed a PC with a
desktop publishing program which had not yet been invented. So, the whole
project languished in a file cabinet all these years. Now the issue is moot
except for the interest some list members may have in knowing about it.
Ken
