Gary Mitchell of the San Jose Astronomical Association pointed out an unusual sunrise in the lunar crater Ptolemaeus. We have succeeded in observing it three times since. Member David Kingsley suggested that I write you for possible inclusion on your web site.

All dates are local (pacific time zone, UTC-8 or -7) evenings.

The story began at Houge Park on Apr.19 2002, during a public star party. Gary Mitchell drew attention to a very subtle shading, which he described as "brush strokes", in Ptolemaeus.

The crater floor was in near-darkness, a soft streaky gray, extending east/west. Over the next 20 minutes, the effect grew more obvious, then slowly the "strokes" lost their softness and became streaks of light.

Subsequently, I tried to observe "Sunrise at Ptolemaeus" on June 17, but was interrupted. I returned to see the end of the phenomenon.

At Redwood Middle School Dec.11, 2002, we again saw the brush strokes. It's gradual enough that we were able to point it out to several of the students, who were able to watch as the illumination was gradually changing over about 30 minutes, from first hints until the light streaks gave us an illuminated crater.

Another opportunity came on Dec.30 2003. The shadow was seen, but 20 to 30 minutes before my predicted time. I was myself clouded out; the timing was by another observer, and we may have "called" it differently.

I find times for which the lunar co-longitude of the sun is 272.2 degrees. The crater's longitude is 2 degrees, so the sun is barely above the horizon. The calculation of co-longitude includes libration, so the latter does not need to be included manually. Then a planetarium program is used to learn the elevations of the Sun and Moon. I use the USNO Interactive Computer Ephemeris (ICE), an old PC-DOS public-domain program. See on Bill Arnett's software site.

The effect happens near 1Q moon each month, but the Sun must be well down, and the Moon well up, so most events are not observable at a given place. I have not attempted the corresponding shadow at 3Q, that is, sunset in the crater. For 3Q, the observer must also be well up!