NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Night moon sights
From: Frank Reed CT
Date: 2004 Jan 30, 13:25 EST
From: Frank Reed CT
Date: 2004 Jan 30, 13:25 EST
ffive wrote:
"For some reason I'm not sure of even on a clear night (no visible cloud) the
glittering reflections seem to begin a little way short of the horizon. "
Yes, I agree. Let's see... I think the principle is fairly simple. The reflection of the Moon's light is necessarily coming from a point down inside the trough of each wave (that's the only way to get "angle of incidence = angle of reflection"). So at a certain distance away from the observer, the crest of the wave in front will block the reflected ray from the trough behind it. The shimmering light beneath the Moon should stop well in advance of the true horizon --which is just what we observe. For an idealized waveform, you could even work this out mathematically and write down a "dip short" for the Moon's "shimmer" horizon. Given height of eye, observed Moon altitude, and wavelength of the surface waves, the true horizon would be found at some calculable number of minutes of arc above the "shimmer" horizon. In practice, this solution based on an idealization would almost certainly not be useful.
Hmmm. Then again, with modern ray-tracing and realistic modelling of the 'chaotic' surface of the ocean... perhaps there is some useful calculational result.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"For some reason I'm not sure of even on a clear night (no visible cloud) the
glittering reflections seem to begin a little way short of the horizon. "
Yes, I agree. Let's see... I think the principle is fairly simple. The reflection of the Moon's light is necessarily coming from a point down inside the trough of each wave (that's the only way to get "angle of incidence = angle of reflection"). So at a certain distance away from the observer, the crest of the wave in front will block the reflected ray from the trough behind it. The shimmering light beneath the Moon should stop well in advance of the true horizon --which is just what we observe. For an idealized waveform, you could even work this out mathematically and write down a "dip short" for the Moon's "shimmer" horizon. Given height of eye, observed Moon altitude, and wavelength of the surface waves, the true horizon would be found at some calculable number of minutes of arc above the "shimmer" horizon. In practice, this solution based on an idealization would almost certainly not be useful.
Hmmm. Then again, with modern ray-tracing and realistic modelling of the 'chaotic' surface of the ocean... perhaps there is some useful calculational result.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
