Photo of the Week. Jet contrails dominate a
spectacular dawn sky, reflecting a Sun still below the horizon.
The foreshortening of the more distant trails near the horizon
reveals the atmosphere to be a flat layer close to the ground.
Astronomy news for the week starting Friday, December 15, 2006.
Our Moon fades away in its waning
crescent phase during most of the week, getting closer and
closer to the eastern dawn horizon until Wednesday the 20th, when
it passes new and makes its transition to the evening sky. The
evening of Thursday, December 21st, you might get your first
glimpse of the slim waxing
crescent in southwestern twilight shortly after sunset. On
Monday the 18th, the crescent passes south of Jupiter,
then at almost the same time both Mars and Scorpius's Antares,
but in the afternoon and evening, with the planets out of sight.
Overwhelmed with the light of dawn, Jupiter and Mars are pretty
much out of sight anyway, although a dedicated observer with a
clear eastern horizon might still spot them, Jupiter leading the
way, Mars much fainter. And too bad, since on Monday the 18th,
Mars will pass north of its stellar look-alike and namesake,
Antares (the name meaning "like Ares," the latter the name of the
Greek god of war). Saturn
remains the planet of choice, rising ever-earlier, this week
around 9 PM. Look for it just to the east of Regulus in Leo, the separation slowly increasing, the planet now
in
retrograde motion. At the other extreme of planetary
visibility is
Pluto, which passes conjunction with the Sun on Monday the
18th.
The biggest planetary news is of Earth
. At 6:22 PM on Thursday the 21st (7:22 EST, 5:22 MST, 4:22
PST), the Sun crosses the Winter
Solstice in Sagittarius and
formal
astronomical winter begins in the northern hemisphere (summer
in the southern, the celestial point clearly named by northerners).
On that date, the Sun will lie as far
south (and for northerners as low) as possible (23.4 degrees south
of the celestial equator), and
northern days will be shortest. It then also rises and sets at its
extreme southeasterly and southwesterly points, and will pass
overhead at the Tropic of
Capricorn. Though beginning to move slowly north, days will
continue to get colder as it will take the Sun some time to get
high enough for its heating power to gain the upper hand on the
cooling ground and waters.
As evening twilight draws to a close, look just west of south about
halfway up the sky to find the "Y" of stars that makes the heart of
Aquarius, the Zodiacal Water
Bearer, most of the constellation sprawling to the southeast of it,
though two fairly bright stars (Sadalmelik and Sadalsuud, respectively Alpha and
Beta Aquarii) lie to the west. Down and to the right is Capricornus (the "Water Goat," while
up and to the left is Pisces (the
Fishes), the three marking an ancient "wet quarter."
