Photo of the Week. The head of Draco, up and to the
left of center, stares down at Vega and Lyra, which lie to the far
right. See them at full resolution.
Astronomy news for the week starting Friday, Sepember 18, 2009.
Skylights now resumes its normal weekly schedule. Thanks for your
patience.
The Moon's phases are for the moment fitting the week. As we
begin, Friday, September 18, marks the new Moon, while
on next Friday, the 25th, the Moon passes its first quarter. In between it waxes through its crescent phase, the first twilight glimpse to
be had the evening of Saturday the 19th. It's no wonder how the
week, with the quartering of the Moon plus the seven moving bodies
of the sky (Sun, Moon, Mercury through Saturn), came to be. The
month of course comes from the 29.5-day period of the phases.
Quartering it gives a bit over a week, the fit we have at the
moment rather fleeting. Watch the evening of Wednesday the 23rd as
the Moon approaches Antares of Scorpius.
The week features various other passages. First, Mercury invisibly goes
through inferior conjunction with the
Sun (more or less between it and us) on Sunday the 20th. Much
better, on the morning of the same day, Venus passes a mere half a degree -- the angular diameter of
the full Moon -- north of Leo's Regulus, the brightness contrast
quite huge, Venus 125 times brighter than the star.
The big passage of course is that of the Sun over the Autumnal Equinox in Virgo on Tuesday the 22nd
at 4:19 PM Central Daylight Time
(5:19 EDT, 2:19 PDT), when formal astronomical autumn begins in the
northern hemisphere (spring in the southern). On that day, the Sun
will rise due east, set due west, be up for 12 hrs and be down for
12, rendering days and nights equal, hence, "equinox." It will
also set at the north
pole and rise at the south pole, giving
the intrepid southern polar scientists a break. All that said,
refraction in the Earth's atmosphere and the finite diameter of the
Sun delays the north-pole setting and advances the south pole rise
for a bit and makes our day a bit longer than night.
Jupiter, now transiting the meridian to the south around 10 PM
Daylight Time, is glorious as it
retrogrades still in northeastern Capricornus. You then do not have that long to wait
until the rising of Mars just before
local midnight (1 AM Daylight), the red planet gliding through the
stars of central Gemini. By
3AM Jupiter is down, but then some two hours later up comes Venus to
dominate the sky, the brilliant planet now in Leo, and we are back
to the conjunction with Regulus on Sunday the 20th.
As the Big Dipper sets in the
northwest, Cassiopeia, opposite,
rises in the northeast. Look for her "W" shape, or her "Chair,"
depending on how you look at it. The celestial Queen is known for
her lovely Milky Way, some clusters, and a few very odd stars
that are some of the most luminous in the Galaxy. To the east lies
the hero Perseus, which harbors the
"Demon Star," Algol, and the
superlative double cluster.
