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Re: Seeing Moon rising an setting ?
From: Jeremy C
Date: 2010 Feb 19, 12:32 EST
From: Jeremy C
Date: 2010 Feb 19, 12:32 EST
Well moon rise is difficult to observe in general. Often it is during
the day which makes for difficult observations due to haze and relatively low
contrast of the moon near the horizon. At night is easier to see, but even
looking for it, I often don't see the moon until it is a degree or more above
the horizon, again depending on the actual atmospheric conditions. The
same holds true trying to observe a star or planet. I was gunning for an
amplitude of a planet and had a heck of a time as the body (even a very bright
Venus) disappeared from view as it passed below a degree above the
horizon.
For my amplitude observation this summer, I had pre-calculated both time
and azimuth and had my Alidade set up. Moonrise was about the time of
nautical twilight so the haze of night had not yet set in, yet the sky was dark
allowing for maximum contrast. The air was also clear as I
mentioned. I was looking through the telescope the moment the upper limb
broke the horizon (when the moon was on the celestial horizon). I also
made an observation when the center of the body was on the visible horizon which
can also yield an amplitude.
The previous time I was not looking for it, but the moon was just off the
port bow and my lookout and I at first thought it was a ship's running
light. After it rose a bit more, I was more sure of what I was looking at,
and wished that I had recognized it sooner to get an amplitude. This was
again a very clear night, but this time it was on the midnight watch, so about 1
AM.
I can't say that I make a huge effort to observe the moon at rising, but I
often try to watch it set while I'm on watch with little success. I
certainly would take this as hard and fast evidence as I have not tried to be
scientific about it.
Jeremy
In a message dated 2/19/2010 4:30:21 A.M. Eastern Standard Time,
marcel.e.tschudin@gmail.com writes:
Thank you, Jeremy, for mentioning your experience. From what you say
it seems indeed not to be possible to see the moon at the horizon
under "normal" atmospheric conditions except under an exceptionally
clear sky. You wrote "seeing the actual limb on the horizon at sea is
quite a bit more rare than observing the sun rise or set" and "I have
seen the moon rise twice in the last three years". In order to get a
better feeling on how rare: Resulted the two observations just by
"accidental" noticing that an amplitude observation would be possible
or did you over the three years regularly look out whether it would be
possible to take such an observation?
Marcel