NavList:
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 6, 18:23 +0300
From: Marcel Tschudin
Date: 2012 May 6, 18:23 +0300
Alex,
These few observations were at night. The (full) moon just gradually faded out when approaching the horizon. Like a lamp when you slowly turn the dimmer. My observations could however be related to pollution. I'm still interested to know better under which conditions a moon set (or rise) is actually visible. Yes the visibility of the horizon at night is a problem; one possibly could not recognise that an object sets behind a thin cloud layer slightly above the horizon. There happen to be very often some clouds. From the time the moon completely dimmed away its altitude was calculated to be above the horizon. Also, in case of setting behind something one would notice that part of the shape would be hidden. This was different. You just have a blotch of light which gradually disappears.
Marcel
These few observations were at night. The (full) moon just gradually faded out when approaching the horizon. Like a lamp when you slowly turn the dimmer. My observations could however be related to pollution. I'm still interested to know better under which conditions a moon set (or rise) is actually visible. Yes the visibility of the horizon at night is a problem; one possibly could not recognise that an object sets behind a thin cloud layer slightly above the horizon. There happen to be very often some clouds. From the time the moon completely dimmed away its altitude was calculated to be above the horizon. Also, in case of setting behind something one would notice that part of the shape would be hidden. This was different. You just have a blotch of light which gradually disappears.
Marcel
On Sun, May 6, 2012 at 5:06 PM, Alexandre E Eremenko <eremenko@math.purdue.edu> wrote:
Marcel,You probably mean in daytime... How about night?
In some NavList contributions during February 2010 on "Seeing Moon rising
an setting ?" I questioned whether it would generally be possible to see
the moon actually setting (or rising). The extinction of the atmosphere
close to the horizon was at least during my (few) observations too strong.
I understand that horizon will be invisible, but the moment of disapearance of the Moon at night should be clearly detectable, ?
Alex.