Skylights featured five times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
, 5
Photo of the Week. Marshmallow clouds drift beneath
a pale sky.
Astronomy news for the week starting Friday, December 30, 2005.
'Tis the year's end, and a Happy New Year to all, as this Saturday
night the clock rolls over to 2006. The year ends, and Skylights'
week begins, with the new Moon on Friday, December 30, giving us a
reverse "blue moon" effect (wherein there are two full moons in a
month), December 2005 having two NEW Moons. The rest of the week
is spent with the Moon in its waxing
crescent phase. In celebration of the new year you can get
your first look at the Moon the night of Sunday, January 1, when it
will appear low in the southwest in twilight to the left of Venus,
the brilliant planet now setting ever earlier in twilight and
rapidly disappearing from view. Early in the lunar cycle the
nighttime side of the Moon will be bathed in Earthlight. On Monday the 2nd and Tuesday
the 3rd, the Moon will respectively (and invisibly) pass to the
south of Neptune and Uranus.
As
Venus vanishes, the early night sky is taken over by Mars
(still in Aries), which transits
the meridian to the south just before 8 PM, and
Saturn (yet in Cancer), which
rises about an hour earlier. Though Mars has faded some from its
earlier glory, it still shines at the minus first magnitude, and is
brighter than all but the two brightest stars, Sirius and Canopus. Saturn (at magnitude zero
brighter than all but the top three stars, number three Alpha Centauri) then transits the
meridian at 2 AM, followed nearly an hour later by the simultaneous
setting of
Mars and the rising of
Jupiter, whose glowing brightness no star can match. Now in
western Libra, Jupiter falls well
to the east of Virgo's Spica.
Far fainter, the asteroid Vesta (the fourth discovered), will pass
through opposition with the Sun on
Thursday the 5th. At faint sixth magnitude in central Gemini, it is just barely visible
to the naked eye (given excellent vision in a dark location),
making it unique among such bodies (the asteroids a collection of
planetary debris mostly between Mars and Jupiter).
Meteor showers come from the debris of comets, not asteroids. Keep
your eye out for one of the major showers of the year, the Quadrantids, which peak
the morning of January 3, and that come out of the defunct
constellation Quadrans, which
lies near the Big Dipper.
On New Year's Day, the Moon will pass through perigee,
where it is closest to the Earth. Just three days later, at about
9 AM CST on Wednesday the 4th, the Earth then passes through perihelion
, where it is closest to the Sun, 147 million kilometers (91.4
million miles), 1.7 percent closer than average. Since perihelion
takes place in the heart of northern winter, solar distance clearly
plays no significant role in the
seasons, which are caused by the 23.4 degree tilt of the
Earth's rotational axis relative to its orbital axis. Since ocean
tides depend on the inverse cube of the distances between the Earth
and the Moon and Sun, they will be especially high (and low) at
this new Moon. Tides slow the Earth's rotation, and to synchronize
clocks with precisely-kept "atomic time," a "leap second"
will be added at midnight as the Old Year passes to the New (giving
61 seconds to the last minute).
Orion and his cohort of bright constellations are now making a
serious impact on the nightly sky, Sirius in Canis Major rising as twilight ends. Watch for them as
they cross the sky during the wintery nights. Meanwhile in the
northeast, the Big Dipper is rising. The Little Dipper, however, is at its low point beneath the
ever-constant pole.
