NavList:

Just to see "how low you can go", I did a run of morning sun sights as close to the horizon as possible. The sight tube come into its own for this purpose, with the sun disc being as small as possible to get the upper limb on the thin sliver of mirror. Any magnification at all and the disc is just too big. I wanted to get as close to a longitude LOP as possible, near 90 azimuth. (Hc is calculated by USNO site) The altitudes are too low for the almanac refraction tables so the USNO refraction figures are used. Refraction changes very fast.

March 15
ZD +7 Pacific daylight time
WE zero
IC -0.24
Mirror AH
All upper limb so -30 min. correction applied.

7-18-45
Ref -4.0
Hs 4*11.6
Ho 1*31.4
Hc 1*33.1
a= 1.7 away
azimuth 93.6

7-19-48
Ref -2.9
Hs 4*35.0
Ho 1*44.2
Hc 1.46.0
a= 1.8 away
azimuth 93.7

7-20-56
Ref -1.8
Hs 5.01.8
Ho 1*58.7
Hc 1*59.8
a= 1.1 away
azimuth 93.9

I though the results were very good under the circumstances. Even using the no-maginification sight tube only a sliver of the disc was visible in the mirror. This was only possible using a first-surface mirror since the ghost images of a regular mirror would make low angle viewing impossible. The sights were taken with the morror on a 36" high table and kneeling about 15-20 feet away from the mirror.
Regards, Randy
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