PHILOLAUS LUNAR SUNRISE RAY Observer: Tony Donnangelo Date/time of observation: 2003/06/10 01:15 U.T. Site location: Hummelstown RD 3, PA, USA (40.27° N., 76.75° W.) Site elevation: 362 feet (110 meters) Site classification: Suburban Instrument: Takahashi FS-102 Magnification: 91x, 137x, 273x The evening was almost totally cloudy. At 01:00 U.T., with civil twilight about to end, there was a hole in the clouds. I quickly set my scope up. I observed crater Philolaus for about a minute, when clouds obscured the moon again. Over the next hour, I had approximately two minutes of visibility, and then ended my observing session. I usually wouldn’t attempt observing under those conditions; however, the weather has been horrendous this spring, with very little opportunity to observe. I wanted to make an attempt to see this recently reported ray. Visibility was decent and steady for the few minutes that were available. Crater Philolaus was prominently illuminated, with the northern exterior wall abutting the terminator. The rim was totally illuminated, except for a section along the western wall. The floor of the crater was in total shadow. I’m skeptical of the previously reported observation in Philolaus as being a lunar light ray. According to Virtual Moon Atlas, the crater has two symmetrical and separated mountains. The illuminated area inside the crater appeared to be the crest along the length of the southern range. The light beam was broken and ragged with a width that varied greatly along its length, as mountain peaks or a crater wall might appear. The light beam curved northward on the western end, which would follow the contour of the interior mountain. On the most western end, the illumination was broader and oval shaped. This would be consistent with a feature in that area.

As a follow-up to my original observation of Philolaus, I took this image last night, 05/12/03 UD at 00:29 UT. I used an 8"SCT, f/10 with a Logitech AstroCam CCD camera. I have marked the suspect area in the copy image. I'm not convinced that this is a sunrise ray. I suspect that it is the illumination of a part of the crater rim wall, south side, where there appears to be a "cleft" or "groove". This feature has a shadow that makes the crater appear wider than it really is and appears to "mimic"a sunrise ray. Either way, this is an interesting feature for further study. If there is any other observer who can shed some light on this, pardon my pseudo-pun, I would welcome the feedback. I'm also reaserching the Consolidated Lunar Atlas to confirm or deny my hypothesis. I'll keep you posted.(This is an image from the Consolidated Lunar Atlas, Photo # C4079. I have marked Philolaus crater in red. You can see something within the crater which looks like a sunrise ray. However I'm still not convinced that it is a sunrise ray.) Regards, Daniel del Valle Clear and Steady Skies, Daniel del Valle Location: 18.26N, 67.09W Aguadilla, Puerto Rico

From: David Ryle

06/10/2003 2-3UT & 4UT
Wichita Falls, Tx 33.824N 98.544W
Seeing fair 5of10, transparency low 3of10, 80deg.F, SW wind 15MPH
8"f/6 reflector at x260

A curious look at Philolaus for the predicted sunrise ray left me with more questions than answers. The first impressions were of a bright shaft of light traversing the floor of the crater which is positioned at an oblique angle. Upon careful observations I could make out a definate ridge in the foreground (south) of the crater rim. This ridge seems duplicit in that there is more than one ridge which gives the visual equivalent of a wider crater wall to the south than what is actully there. A difficult visual task to discern even under good conditions. The widened ridge is easily seen in the Lunar Orbiter gallery shot iv_164_h2 from the Luner Orbiter Photographic Atlas of the Moon.