Photo of the Week. The Ohio River reflects an autumn
sky. (See the water's beauty at full
Astronomy news for the week starting Friday, December 5, 2008.
The week is bookended by lunar "phases of the moment," beginning
with first quarter on Friday, December 5,
which is passed in daylight with the Moon climbing
the eastern afternoon sky. The quarter is then followed by a week
of the waxing gibbous, which ends with the
full Moon on Friday the 12th. With the Sun
approaching the Winter Solstice in
Sagittarius, the full Moon will be
just shy of the Summer Solstice in
Gemini and thus -- for those of
us in mid-northern latitudes -- very high in the nighttime sky.
The only planetary passage is with Uranus on
Saturday the 6th, the Moon going to the north of
William Herschel's planet.
On the same day as the full phase, the Moon will also pass its perigee, where
it is closest to the Earth. Given that we are also approaching
perihelion (where the Earth is closest to the Sun) early in
tides will be especially high (the size of the tide responsive
to the inverse cube of the distances between Earth and Moon or Sun).
This week marks the run-up to the Geminid meteor shower, which comes from the flakings of
Comet Phaeton, once thought to be an asteroid. Though the shower
peaks the night of Saturday the 13th (the morning of the Sunday the
14th), you might see some meteors by the end of the week (the
bright Moon unfortunately making a bit of a mess of
Mars, lost in
western twilight for the past couple months, is finally officially
gone from evening, as it passes conjunction with the Sun on Friday
the 5th. We'll not catch it in the morning skies for some time.
The evening still, of course, belongs to Venus and Jupiter. These
two brightest planets (Venus by far the brighter) have switched
places, Venus now to the east of the giant planet. While we start
the week with both in northeastern Sagittarius, Venus passes across the border into Capricornus on Wednesday the 10th.
Both now glorious in the southwest after sunset, Jupiter does not
set until after 7 PM, well after the end of twilight, Venus not
'till around 7:30. Then Saturn (in Leo) enters the scene, as it makes a
transition to rising before midnight later in the week.
While the shortest day of the year occurs when the Sun passes the
Winter Solstice, which it will do on December 21, this week marks
the time of the earliest sunset, which takes place around Sunday
the 7th. The difference is caused by the slight eccentricity of
the Earth's orbit and the 23.4 degree tilt of its axis, which at
this time of year causes the Sun to get ahead of its average
position, which is used for steady timekeeping.