Astronomy news for the week starting Friday, January 21, 2011.
Having passed its full phase on
Wednesday, January 19, the Moon has now
slipped into its waning gibbous
phase, which ends at third quarter on
Wednesday the 26th, after which the Moon enters the beginning
portions of the waning crescent. The
week itself begins with the Moon going through perigee, where
it is closest to the Earth, nearly six percent closer than average,
the effect not visible to the naked eye.
The nights of Sunday the 23rd through Tuesday the 25th (actually
the following mornings) find the Moon plowing through Virgo and past
Saturn, in the middle of the trio of dates moving some 8
degrees south of the ringed planet. The view the night of Monday
the 24th will be especially good, with Saturn, the Moon, and the
star Spica making a nice triangle,
which rises with Saturn up and to the left of the Moon, Spica down
and to the left. At week's end, on the morning of Friday the 28th
the waning crescent passes through the three-star head of Scorpius, northwest of the star Antares.
Jupiter slips ever farther west, the giant planet now in the
southwestern sky as evening falls and setting due west shortly
before 10 PM, so look early. But just over an hour later, up comes
Saturn, which rises about an hour before midnight, then crosses the
meridian to the south in Virgo to the
northwest of Spica about 5 AM, just under an hour before the onset
of dawn. By that time, Venus, rising at 4 AM, is well up and
glorious in late morning skies.
For all the prominence of Venus and Jupiter, however, this is
really fainter Saturn's week, as on the night of Wednesday the 26th
it begins its
retrograde (backward) motion, the result of Earth preparing to
pass between it and the Sun. The planet will then begin to move
westerly against the stars, ever so slowly pulling away from Spica
instead of drawing toward it.
'Tis the season for brilliant far northern constellations, in particular Cassiopeia, whose "W" rides high just
past the meridian as darkness falls. To the east of her, we find
the star streams of Perseus, who in myth rescued her daughter Andromeda from the jaws of Cetus. Farther east rides Auriga, the Charioteer. In the
deep cognate southern hemisphere, Achernar sparkles at the end of the
River Eridanus north of Hydrus, the Water Snake. To the east,
however, lie some of the sky's more obscure constellations, Horologium (the Clock), Caelum (the Engraving Tool), and Reticulum (the Net), whose proper
viewing requires one to be south of the Tropic of Cancer.