Alexander Lunar Sunset Ray

Observer: Tony Donnangelo 
Date/time of observation: 2004/10/05 03:52 U.T.
Site location: Tuscarora State Forest, PA, USA 
Site coordinates: N. 40.51° W. 77.63°
Site elevation:  427 meters (1402 feet)
Site classification: State forest wilderness area 
Instrument: 14.5” Starmaster Dob.
Magnifications: 107x, 152x, 203x
Moon's age: 20d 13:20, Illuminated: 61.9%
Librations: 6.5°, PA 189°, N/S -6.41°, E/W -1.07°
Object: Alexander (greatly eroded walled plain)                                                                                                                                 
Lunar ray coordinates: 12.0°E, 40.0°N

This observation was very rewarding for me. See Dave Mitsky’s initial report. He and I made a dark site trip when he saw a triple ray in this crater. The triple ray was still in progress when we ended our observing session. It was not predicted to occur this month. I believe I saw the remnant of this triple ray at a time after Dave’s final observation. It would be very interesting to see it in its entirety.

I was setup before sunset. Unfortunately, it was completely cloudy until 03:00 U.T. (11:00 p.m. local time), when clearing commenced and the moon became visible within the tree line. Light dew started forming at nightfall and became very heavy by 06:30 U.T. I began observing the moon as it cleared the trees at 03:50 U.T. Seeing was very turbulent, but transparency was good.

A very thin ray was occurring in Alexander. It most probably could be seen, with the likelihood of multiple rays, at an earlier hour. The ray extended from an almost complete break in the western wall to about two-thirds across the crater. It had two segmented shadows from raised areas on the floor.

Part of the eastern wall was in the terminator. The western exterior side was illuminated, and the floor was completely shadowed except for the ray. There were a few bright areas east of the ray and well within the terminator. One bright spot was in line with the ray, one to the south, and three to the north, some might be summits of craters A and B. Craters A and B were in shadow and not discernable.

Crater Calippus, southwest of Alexander, was well out of the terminator. It had a very bright white area on its crest. Its floor was completely shadowed except for an illuminated raised area. The shape of this area gave the peculiar appearance of a bikini bathing suit bottom. This perception became even more apparent as time lapsed. It remained observable throughout the remainder of my session.

By 04:55 U.T., the ray began to shorten and narrow. Approximately one-half of Alexander was now within the terminator. Over the next hour, it continued to shorten and narrow considerably. By 05:55 U.T., the ray was thread thin and shortened from the west toward the east. Within another thirty-five minutes, it was extremely dim and almost completely gone.