I also just got in from a brief look at the moon with the 7 inch Starmaster.
It's wet and foggy out there, and skies have mostly clouded over at
Stanford after a brief clear spell around 4 or 5 pm.
However, seeing was actually very steady when I first looked through
the scope around 6:50 pm. The moon was varying in brightness as thin
and thick spots in the clouds would pass by. During the brighter
moments, I had a very interesting view of the Ptolemaeus shading
effect that Jim Van Nuland mentioned a week ago (see his post below).
I could definitely see the several subtle brushes of light extending
from east to west across the crater. It reminded me of a beautiful
set of light rays I also caught gradually widening across Plato on a
particular night last June
(http://observers.org/reports/2003.06.07.3.html). The Ptolemaeus
shading effect should be going on right now so take a look if you
have a scope set up and your skies are better than mine are near Palo
Alto..
Jim, I would be interested in your predictions of when to look for
the Ptolemaeus brushes again in 2004. Could you also predict when
the illumination be the same again to reproduce three parallel rays
of light across Plato observed around 9:45 PDT on June 7th, 2003???
I should definitely learn how to do these calculations so I can run
other predictions. I would not have set up tonight and seen this
effect if I hadn't read Jim's earlier prediction.
David Kingsley
At 3:22 PM -0800 12/23/03, Jim Van Nuland wrote:
>On the evening of Dec.30, an unusual shadow may be visible in the
>large lunar crater Ptolemaeus.
>
> 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 comes Dec.30 2003, from about 7 to 8 pm, PST. The
>Sun is 22 degrees down, and the moon 55 up. All we need is a clear
>sky. Start somewhat earlier if you are not confident of which crater is
>Ptolemaeus. See Rukl chart 44. It's the first big crater on the
>terminator, coming from the north.
>
>CALCULATIONS:
> I find times for which the lunar co-longitude of the sun is 272.3
>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 <http://www.seds.org/billa/ice/ice.html> 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!
>
>Clear Skies!
>--
>Jim Van Nuland, San Jose (California) Astronomical Association
-- David Kingsley, Ph.D. Professor of Developmental Biology HHMI and Stanford University School of Medicine Beckman Center B300, 279 Campus Drive Stanford, CA 94305-5329 (650) 725-5954 (office), (650 725-7739 (fax)