Celestial Exercise for Part 8: First Sight Reduction
23 June 2021 · 40 min · 4K views · Bay of Biscay
What this video covers
Celestial navigation requires a systematic five-step process to reduce a sun sight into a position line.1:21 Using a sextant, the navigator measures the sun’s altitude and applies corrections for index error and dip to determine the observed altitude (Ho).1:34 The process involves calculating the sun’s declination and Greenwich Hour Angle (GHA) from the Nautical Almanac for the exact time of observation.10:38 By selecting an assumed longitude that results in a full-degree Local Hour Angle (LHA), the navigator uses the H.O.21:08 249 Sight Reduction Tables to find the calculated altitude (Hc) and azimuth (Zn).23:22 Comparing the observed altitude to the calculated altitude yields the intercept, which represents the distance in nautical miles from the assumed position toward or away from the sun.32:54 When the observed altitude is lower than the calculated altitude, the vessel is positioned further away from the sun’s geographic position.31:57
Boats in this video
More from Leon Schulz, Reginasailing
From Leon Schulz, Reginasailing — see the channel’s boat, crew, and every analysed video.
The Sailing Directory Newsletter
One email with the fleet's best finds — the moments, boats, and stories worth your watch time. Enter your own address to get your own copy.