NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Timesight at sunset?
From: Doug MacPherson
Date: 2013 Jan 10, 10:25 -1000
From: Doug MacPherson
Date: 2013 Jan 10, 10:25 -1000
Thanks Greg and Marcel!
Sent from my iPhone
Sent from my iPhone
Doug,
Your exercise is of interest. Some of you may remember that my interest is refraction near the horizon. I was able to make during a few years observations of the setting sun. Some of these observations consisted also in timing the last sun ray.
Greg, you analysed Doug's observation and wrote:The online calculator has your sunset observation within 6 NM. Not bad. Your watch could be slow some seconds though. Give it a time check double check.
The reason is possibly not the watch. If I interpret a first analysis of my observations correct then the last ray seems indeed to happen a moment earlier compared to the time of the upper limb touching the horizon. A preliminary result indicates this difference to be about 2 to 3 moa (scattering +/- by about the same amount). At the latitude of my observations (41 N) this corresponds to a timing difference of about 15 s.
Performing the sight reduction again but setting now the instrument reading instead to 0 moa to the value from the preliminary analysis, 2.5 moa, then the intercept does indeed reduce from -5.7 nm to -2.6 nm.
Marcel