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Re: Sun SD, Sextant precision, SNO-T
From: Lisa Fiene
Date: 2004 Oct 11, 07:49 +1000
From: Lisa Fiene
Date: 2004 Oct 11, 07:49 +1000
Hi Alexandre, According to the Sun Ephemeris for 2004, the following is indicated: October 10th - 1922.1" (for diameter - just halve for SD) = 16'0175" See: http://sunearth.gsfc.nasa.gov/eclipse/TYPE/sun2.html#su2004 or http://www.cadastral.com/2004oct.htm Hope this helps, Lisa Alexandre Eremenko wrote: > Can anyone tell me more precise value of > the Sun radius on October 10? > (This quantity is called "semidiameter, or SD" in the > almanach. The almanach gives for October 10 > the value of 16.0', but I noticed that it gives > 16.1' beginning from October 12, and the refraction table > implies the average value of 16.15 for October-March. > The "Astronomical Almanach" or maybe some software could probably > give it more precisely (I need one more digit). > > The reason I am asking: This morning I have fixed all > (hopefully!) problems with my inverting scope, and tried > to fing the index correction from Sun observations > (with a fixed scope and more experience than I had last time:-) > The results are the following: > (everything is in angular minutes. "UL" is the sextant reading > when the reflected image touches from above, > -LL is when it touches from below. "4SD" is the sum > of these readings, "-IC" is the difference divided by 2, > the negative of the Index Correction.. > > 1. Rotating the drum in the decreasing direction: > UL 32.5, 32.3, 32.5, 32.4, 32.3, > LL 32.0, 32.1, 32.0, 32.1, 32.0, > 4SD 64.5, 64.4, 64.5, 64.5, 64.3, Almanac: 64.0 > -IC 0.25, 0.1 0.25, 0.15, 0.15 Average: -0.2 > > 2. Rotating the drum in the increasing direction: > LL 32.0, 32.0, 32.0, 32.1, 31.9, > UL 32.2, 32.5, 32.6, 32.5, 32.5, > 4SD 64.2, 64.5, 64.6, 64.6, 64.4 Almanac: 64.0 > -IC 0.1, 0.25, 0.3, 0.2, 0.3 Average: -0.2 > > These results indicate that my index correction is > something between -0.2' and -0.3' (Which is consistent > with my previous Sun observations, but NOT with the star > observation; star observation give consistently 0.0'. > Today will repeat star observations > with my newly fixed inverting scope. > > The problem with the Sun observations above > is that my measurements of > Sun's SD indicate > that it is closer to 16.1' rather than 16.0'. > This explains my question in the beginning. I have to multiply > the almanac value by 4. This increases the almanac rounding > error by the factor of 4. > > (The Russian manual says: if your measurement of 4SD is > within 0.4' from the almanac value, your measurement is OK. > Otherwise it should be repeated. > My measurement is on the boundary:-) > > (My apologies in advance to those list members who consider > all this activity "splitting of a hair":-) > > Alex. > > -- Kind regards Lisa Fiene *************************** CopyCare Pacific Pty Ltd Lizard Tunes ABN 93 101 046 888 PO Box 314 Ourimbah NSW 2258 Australia Phone/Fax: (02) 43 627 583 International: 61-2-43 627 583 E-mail: lisa@copycarepacific.com Web: www.copycare.com/content/local/ccpaceng.asp