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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Longitude by Sunset
From: Marcel Tschudin
Date: 2012 May 7, 01:54 +0300
From: Marcel Tschudin
Date: 2012 May 7, 01:54 +0300
@ Alex:
No, these observations were not related with clouds, at least not where the moon was. I say this because I observed it with great attention. The moon was first clearly visible. A cloud would have suddenly or unevenly changed its brightness. This was not the case. It just got slowly fainter and fainter.
@ Greg:
If the island is sufficiently far it will only rise a little above the horizon. You still could could find out whether the moon sets behind the island or whether it disappears before reaching this low altitude.
@ h.a.c. van Asten:
I am not sure if I understand what you mean. The parallax is used for converting earth-centered coordinates to topocentric coordinates. When looking at the setting moon one does it as a topocentric observer, yes, where the light of the moon is refracted from the atmosphere. However, if I do not want to measure something the coordinates, parallax and refraction are not relevant. The observed disappearance of the moon was due to atmospheric extinction.
Marcel
No, these observations were not related with clouds, at least not where the moon was. I say this because I observed it with great attention. The moon was first clearly visible. A cloud would have suddenly or unevenly changed its brightness. This was not the case. It just got slowly fainter and fainter.
@ Greg:
If the island is sufficiently far it will only rise a little above the horizon. You still could could find out whether the moon sets behind the island or whether it disappears before reaching this low altitude.
@ h.a.c. van Asten:
I am not sure if I understand what you mean. The parallax is used for converting earth-centered coordinates to topocentric coordinates. When looking at the setting moon one does it as a topocentric observer, yes, where the light of the moon is refracted from the atmosphere. However, if I do not want to measure something the coordinates, parallax and refraction are not relevant. The observed disappearance of the moon was due to atmospheric extinction.
Marcel
On Sun, May 6, 2012 at 7:45 PM, Alexandre E Eremenko <eremenko@math.purdue.edu> wrote:
Marcel,Perhaps there were clouds?
These few observations were at night. The (full) moon just gradually faded
out when approaching the horizon.
I am trying to recollect, but cannot remember any instance
that I've seen a moonset over the sea:-(Me too.
I'm still
interested to know better under which conditions a moon set
Alex.
