Thursday, July 27, 2006

Bracketing the New Moon

Panels left to right: young crescent(1d19h53m), new moon (0.0d), last crescent (28d17h28m)
red mark indicates libration
snippings from Virtual Moon Atlas

Session Name: 20060726.1900
Location: Top of the Lawn (TotL), Central Park, NYC (Google Map of
where I was)
Site Classification: Urban
Date/time: 26 July 2006, 7:00PM ~ 10:30PM
Sunset: 8:17PM
Moonset: 9:25PM
Handheld Binos: Fujinon 7x50, fov 7.5°
Tripod-mounted Binos: Takahashi 22x60, fov - 2.1°
Weather History
Transparency/Seeing (1 worst - 5 best): 2/2
NELM: --
Conditions: Low thick clouds floated above a very hazy sky along the horizon.
Observing party: Charlie and me

Mission accomplished: our first opposing crescents.

Mother Nature could not get the best of us. At 8:25PM from TotL, I spotted the setting young 1d19h53m waxing crescent Moon through seemingly heavy haze and some clouding above the tree line along the western horizon in handheld Fujinon 7x50 bins. I then put the crescent Moon in the tripod-mounted Tak 22x60 bins. Typically, a 3.2% illuminated disk does not present any difficulties. However, in spite of these challenges today, a 150° arc of crescent was teased from the white background sky.

The crescent shape appeared to extend the length for 2:00 ~ 7:00. The greatest width of the illuminated portion appeared around 5:00~ish. The contrast was low and the crescent was faint so I really didn't notice any kind of uneven illumination. I looked for any hint of Mare Australe but didn't get any. I was thinking that the bins were limiting because I couldn't increase the magnification. As the sky darkened and the Moon descended a small gain in brightness was realized. The gain was not substantially large but large enough that a naked eye sighting was possible. This was confirmed by a few other persons besides Charlie and myself.

Not what I had in mind but Charlie mentioned this was our first opposing crescent moons. I would have rather captured yesterday's crescent moon which would have resulted in a 39 hour interval. With today's observation this yields a 62h50m interval.

At 8:40pm the crescent was seen naked eye. I could only make out a quarter of the arc, like 90°. I had this same impression the entire time until it set behind the trees. The crescent Moon sank nicely into a small nook created by overlapping trees.

We shared the view with folks who stopped. Most memorable was the mom and 3 children. I invited them to have a look and offered to lower the tripod. Mom asked them twice but they said it was okay. I handed the mom my 7x50 bins suggesting that she relax her gaze and described where to look. She got the crescent pretty quickly. The kids said they wanted to look so down went the tripod for them. They all were able to see it saying how thin it was. While the bins were low another couple of ladies stooped down to give it a try. It was obvious when they got it as the ooohs and ahhhs were expresed with a lot of excitement.

Once again I got to demonstrate how Charlie and I bracketed the New Moon by observing the last and young crescents. This is more commonly referred to as "opposing crescents". The Tak bins were the Sun, one of the women was Earth, and my trusty mechanical pencil was the Moon. A small sweep of my arm past the bins with narration at three points explained it clearly to all that was willing to listen.

Can't keep what you have unless you give it away.