SKYLIGHTS
Astronomy news for the week starting Friday, January 19, 2001.
This week holds the new Moon, passed the morning of Wednesday, the
24th. Six hours later, it passes apogee, when it is farthest from
the Earth. Before that date you can see the earthlit waning
crescent in the morning hours to the east before sunrise, and
afterward the reversed waxing crescent in the west after sunset.
The Moon will be technically visible in western twilight the night
of Thursday, the 25th, nearly in conjunction with (and below) the
planet Mercury, but both will be quite difficult to see. By the
night of Friday, the 26th, however, the slim lunar crescent (now
well up and to the left of Mercury) will be quite visible.
Mercury's visibility will improve until early next week, when it
reaches greatest eastern elongation from the Sun.
Earlier in the week, on Monday the 22nd, Mercury passes close
conjunction with Uranus, a quite-invisible event. At the end of
the week (on Thursday the 25th), Uranus's near-twin, more-distant
Neptune, finally passes conjunction with the Sun to become a
morning object. Uranus will follow in early February. Though
Mercury will be, as usual, hard to find, Venus will not, as it
continues to blaze away in the southwestern evening sky.
In a highly unusual coincidence, both Jupiter and Saturn cease
their westerly retrograde motions not only the same day (Thursday
the 25th), but within about an hour of each other. It would be
difficult to figure how often this happens without running actual
orbital calculations, but it must be once in hundreds, if not
thousands, of years. Odder still, Jupiter ceases retrograde first
even though it is the more-easterly planet (ordinarily, the more-
westerly ones finish first), a result of Jupiter's being closer to
us than Saturn (4.4 as opposed to 8.6 astronomical units, the AU
the average distance between the Earth and the Sun). Both planets
will thereafter begin to move in their normal easterly direction
against the background stars (for now, of Taurus), Jupiter pulling
away from the ringed planet as it heads for the next constellation
of the zodiac, Cancer.
Taurus (Jupiter and Saturn's temporary home) is at its best in the
early evening around 8 PM. Look for the vee-shaped Bull's head
made by the Hyades cluster, the Seven Sisters (Pleiades) up and to
the right. Aldebaran, the Bull's orange eye, is only situated in
front of the Hyades and is not actually a part of it. Taurus is
one of the few constellations that link to another, the northern
horn (which extends northeast of Aldebaran) tied to bright Auriga,
the Charioteer, which with bright Capella, stands above Orion. The
other linking constellations are northern autumn's Andromeda with
Pegasus and summer's Ophiuchus with Serpens.
