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From: Alexandre Eremenko (no email)
Date: Mon Nov 29 2004 - 01:27:20 EST
Thanks to all who answered about irradiation.
(I rarely look in the "sextant" list; I like
this one much more, for several reasons:-)
On Sun, 28 Nov 2004, Trevor J. Kenchington wrote:
> The better demonstration of irradiation, for members of this list,
> might
> be to measure the semi-diameter of the Sun, under various condition
Actually, this was the main resaon for my questions:
Nov 25 16:00 LT (Sun very low, just before the sunset)
Sextant vertical, Sun SD from the almanac 16.2; 4SD=64.8
Up Low Sum "IC"
31.1 32.5 64.6 -0.2
Nov 25 16:25 LT (Few minutes before sunset)
Sextant vertical:
31.8 32.3 64.1 -0.25
31.9 31.9 63.8 0
31.9 31.9 63.8 0
31.9 32. 63.9 -0.05
Average 4SD: 63.9 (The vertical SD of sun compressed by refraction).
Sextant horizontal (handle down):
33.0 32.9 65.9 0.05
32.8 32.8 65.6 0.
Average 4SD: 65.75 (Irradiation??)
Later, same night: index correction from
stars 0.0 both upright and horizontal and upside down.
An a good lunar the same night.
Nov. 28 LT 15:39
Sextant vertical:
32.1 32.5 64.6 -0.2
32.3 32.1 64.4 0.1
32.5 32.6 65.1 -0.05
Average 4SD: 64.7 (Very close to the truth)
Sextant horizontal:
32.5 32.6 65.1 -0.05
32.8 32.4 65.2 0.2
32.2 32.6 64.8 -0.2
Average 4SD: 65.0 (Irradiation?)
Sextant upside down:
32.7 32.2 64.9 0.25
32.1 32.3 64.4 -0.15
32.6 32.4 64.7 0.1
Average 4SD: 64.7 (Close to the truth again).
Conclusions:
a) It seems that the sextant is quite rigid.
b) In horizontal position I always get somewhat higher
numbers for 4SD than the almanac predicts.
Maybe because of irradiation?
c) In vertical position this seems to be compensated
or partially compensated by refraction.
Alex.
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