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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Calibrating Your Sextant Without Horizon or Collimator
From: Paul Hirose
Date: 2024 Sep 4, 16:46 -0700
From: Paul Hirose
Date: 2024 Sep 4, 16:46 -0700
Lunar distance is not sensitive to time if you use a star at a right angle to the Moon's motion. In other words, stars which would be terrible choices for lunar distance time determination are good for sextant testing. Accurate position is not vital. A 0.1′ change in lunar distance occurs when the observer is displaced perpendicular to the line of sight by 1 / 34 000 of the Moon's range. By mental estimate that's about 12 km. For an example precomputation of a sextant calibration lunar, my Lunar 4.4 program says at 2024-09-21 22:00 UT1, 51N 0E, the Moon is 24° high and Schedar 67°. Sun is 34° below horizon. Position angle, Moon to Schedar, is 13° with respect to the zenith, so the sextant position will be comfortable (inclined to the left 13°). The Moon is gibbous (54° phase angle) and the program recommends the far limb. Refracted distance with standard sea level conditions is 45°44.6' to far limb. The lunar distance rate is only +0.04' per minute time. -- Paul Hirose sofajpl.com
