Photos of the Week.. The Moon (its nighttime side
illuminated with Earthlight) just barely misses a grazing
occultation of Nu Virginis on July 14, 2002, the star seen just to
the left of the upper horn of the bright crescent. The pictures,
taken 5 minutes apart, clearly show the easterly lunar motion. The
irregular outline of the bright crescent (the sunrise line on the
Moon) is caused by high areas catching the first rays of sunlight
contrasted with low basins still in shadow. (The glow to the right
of the crescent is a photographic effects caused by the Moon's
brilliance).
Astronomy news for the short week starting Friday, December 13,
2002.
The Moon, having just passed its third quarter, waxes in its gibbous phase as
it heads toward full on Thursday,
the 19th, around noon in North America. As a result, the not-
quite-full Moon will rise just before sunset the night of Wednesday
the 18th, and the just-past-full Moon will rise just after sunset
the night of Thursday the 19th. The somewhat mysterious word
"gibbous" comes from middle English meaning "humped," rather like
a camel, as the two circular outlines of the Moon, the real edge
(or limb) and the terminator (the day-night division) have
different convex curvatures. Four hours before its full phase, the
Moon passes Saturn
, the planet falling a bit to the west (and somewhat south) of
the Moon the night of Wednesday the 18th, and somewhat to the east
of the Moon the following night.
Since the full Moon is in opposition to the Sun at about the same time
it passes the ringed planet, it holds that Saturn should be near
opposition too, which it is, passing that position on Tuesday the
17th. At that time, it will rise at sunset, set at sunrise, cross the meridian to the
south at midnight, be in the middle of its retrograde motion, and be at its best visibility for the
year. Moreover, it is about as far north as it can get.
With a telescope we get a fine view of the south side of the
famed rings,
which are complex belts of fine ice-coated rocky debris in orbit
about the planet. Moreover still, Saturn is near its perihelion
point, and is about as close to the Earth as it can get, rendering
it especially large and bright. A view with even a small telescope
quickly shows Saturn's largest moon, Titan
. Slightly larger than
Mercury, Titan is the only satellite with a thick atmosphere.
When you are through with Saturn, you do not have long to wait to
see brilliant
Jupiter, which climbs above the eastern horizon shortly before
9 PM. Wait a few more hours now, until roughly 3:30 AM, and find
much-brighter Venus
lofting itself upward, the planet rising almost as early as possible
for this particular apparition.
With astronomical winter nearly on us, the fall constellations are
moving westward. There is still time, though, to admire the bright
southern star Fomalhaut in the
constellation Piscis Austrinus, the
Southern Fish, the star low in the south around 6 PM for mid-
northern latitudes. Immediately to the east you will find the dim
and rather large modern constellation Sculptor, the "Sculptor's Studio." Its major claims to
fame are its peculiar Alpha star, the Sculptor Dwarf
Galaxy (which lies 300,000 light years away), and its
possession of the South Galactic Pole, the direction that lies
perpendicular to the plane of the Galaxy and of the Milky Way
(the North Galactic Pole falling in Coma Berenices).
