Saturday, June 16, 2007

June's 21 hour crescent crescent Moon

Session name: 20070615.1810

Appearance of crescent at time of sighting.
(screenshot of detail below)

I arrived early at TotL East to establish azimuth references on the trees along my western horizon with the setting Sun. The tree line rises from 7° ~ 9° in the area I was working with. This helps to determine where to look and I use the same technique with stars when marking a morning horizon for old crescents. During this time until sunset, I observed Sun with my solar paddle and located Venus in the bins and then naked eye. Kentaurian was one of the many persons that stopped by to enjoy the daytime astronomy. He would be key in observing the crescent at the prescribed time.

I had the wrong mental note of Moon's elevation at the predicted sighting by thinking it was to be 10° (an approximate value at sunset). At 20:44 EDT Moon was 7°27' so following Ken's recommendation we moved further east and on the Great Lawn to get a lower horizon. I had no azimuth references at the new location but Ken suggested landmarks including the Beresford Tower. At 20:50 EDT using Fujinon 7x50 binoculars, the thin crescent was easy to see, unintimidated by the haze and avoiding clouds at Alt/Az of 6°39'/300°19'.. Moments later the tripod-mounted Taks were leveled on the crescent, illuminated along an arc from 3:00 ~ 7:30.

At 20:53, I could discern the moon's limb, a "line" from 3:00 ~ 6:00, naked eye without optical aid. Ken confirmed minutes later with his own naked eye sighting. Naked eye was extremely difficult but visible for next 9 minutes.

Prior to spotting it we were talking about using Mercury as a convenient reference point. It sounded like a great idea and having evaluated the sky and recent experience Ken thought Mercury should be visible. We never saw it. Once our attention was on the crescent, I forgot to look out for Mercury which was 1° higher in elevation and a binocular field (7 1/2°) south along our horizon.

The crescent moon set between a dip in the trees at 21:02 EDT. The water tower and protuberances along the trees' profile provided landmark's to aid in seeing the moon set naked eye. At the time of disappearance, the moon was 4°37' in altitude. For 12 - 13 minutes, we watched the crescent slip across the sky as we skipped along our landscape trying to find an everlasting horizon.

Screenshots providing the details

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images: Screenshots of Planetarium for the Palm, assembled with gimp