Skylights featured five times on Earth Science
Picture of the Day: 1
Photo of the Week. Memories of summer beneath a wide
Astronomy news for the week starting Friday, December 16, 2005.
We are in a somewhat odd situation, as during our week there are no
"phases of the moment." Full Moon took place last Thursday,
December 15, while third quarter will not be passed until Friday
the 23rd, leaving the whole week for the waning gibbous Moon, for which we see less and
less of the lunar daytime side and more and more of the lunar
night. Because of the five degree tilt of the Moon's orbit
relative to that of the Earth's, on the night of Friday the 16th,
the Moon will be about as far to the north as it can get, and thus
for North America about as high as possible when it transits the
meridian near midnight. Watch the night of Sunday the 18th as the
Moon prepares to pass a few degrees to the north of Saturn,
closest approach taking place the morning of Monday the 19th.
Rising now around 8 PM (along with Sirius in Canis Major), the ringed planet has moved well into the
evening. About half an hour later, still-bright Mars crosses the meridian to the south.
By 3:30 AM, Mars is setting, while at the same time Jupiter
is rising, this close match lasting through the end of the
year. The giant planet, shining brightly in the southeast at dawn,
is impossible to miss. In the evening, Venus is
still with us, though fairly low in the southwest and now setting
earlier, just after 7 PM. It enters its retrograde motion (to the
west relative to the stars) the night of Thursday the 22nd. Mercury
rises in the morning sky just as dawn breaks, while at the
other end of the Solar
System, Pluto quite invisibly passes conjunction with the Sun as the week begins.
The big event involves our own planet Earth.
Near noon on Wednesday the 21st,
at 12:35 PM Central Time (1:35 PM Eastern, 11:35 AM MST,
10:35 PST), the Sun crosses the Winter
Solstice in Sagittarius, and
astronomical winter begins in the northern hemisphere, summer in
the southern. On that date the northern end of the Earth's
rotation axis is tilted as far away from the Sun as possible, the
Sun is as far to the south as possible, is overhead at the Tropic of Capricorn (23.4 degrees
south latitude), and is as high at the south pole as it can get.
While the north pole of the sky is marked by Polaris, the "North Star" in Ursa Minor, the southern pole is more
or less blank, indicated by faint Sigma Octantis, in modern Octans, the Octant. This is a poor
time of year for the recognizable part of Ursa Minor, the Little
Dipper. Hard to find if there is any ambient light at all, the
figure now in early evening dips down toward the northern horizon,
while Cassiopeia and Perseus take the overhead stage.