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This evenings star pair observations included Vega Deneb (by sextant) and Alioth Alkaid (by sextant and camera). This time the on-line William's GC calculator was used properly to calculate true star pair distance. The Vega Deneb pair was corrected for refraction using the approximation method of 0.1' per 5* of angular distance. The Alioth Alkaid pair was corrected for refraction using the table provided by Mike Burkes (attached).

Vega Deneb Hc 85*65*
23* 50.1' observed distance by sextant
+0.5' refraction correction (approximation 0.1' per 5*)
23* 50.6' true distance
23* 50.8' true calculated distance by William's on-line calculator
Low 0.2'

Alioth Alkaid Hc 31*37*
10* 27.1' observed distance by sextant
+0.3' refraction correction by table
10* 27.4' true distance
10* 27.6' true calculated distance by William's on-line calculator
Low 0.2'

Alioth Alkaid
10* 28.0' observed distance by camera
+0.3' refraction correction by table
10* 28.3' true distance
10* 27.6' true calculated distance by William's on-line calculator
Hi 0.7'

The camera image was disappointing showing 4' wide stars. Settings were ISO 1600, f 2, 1/8 sec, infinite focus using a fixed prime 50 mm lens. Sextant results were good.

Greg Rudzinski

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