Astronomy news for the week starting Friday, September 20,
2013.
We begin with the Moon just past full,
which took place on Thursday, September 19. During the week, we
thus get to watch the waning gibbous
phase as the Moon heads toward third
quarter the night of Thursday the 26th roughly about the time
of Moonrise in North America. Only a few hours later, the Moon
passes its apogee where it
is farthest from the Earth. The night of Thursday the 26th
(more the morning of the 27th), the
Moon also invades southern Gemini, and will appear nicely to the west of bright Jupiter, with Castor and Pollux farther north.
Moving more or less in opposite directions relative to the Sun, Venus and Saturn are
finally crossing paths, the two setting about the same time about
as twilight ends (8:30 PM Daylight Time). Look the night of
Tuesday the 24th to find them on a line parallel to the twilight
horizon, much fainter Saturn to the right. With Jupiter rising in
the northeast about midnight local time (1 AM Daylight), the
morning planetary show is better. Wait two hours until 3 AM
Daylight to see Mars rising in
eastern Cancer between the bright constellations of Gemini (with
Castor and Pollux) and Leo (with Regulus). At dawn, the two make a
glorious sight Jupiter on top with the star Sirius down and to the right.
The big event, though, belongs to Earth, when on
Sunday the 22nd at 3:44 PM Central Daylight Time (4:44 PM EDT, 2:44
MDT, 1:44 PDT) the Sun crosses the Autumnal Equinox in Virgo and autumn begins in the northern hemisphere
(spring in the southern). On that day the Sun rises due east, sets
due west, and days and nights are equal, ignoring twilight each
about 12 hours long. The Sun also technically sets at the north pole and
rises at the south pole. Go
down there and watch, but bring a good coat.
In early evening, look toward the meridian to the south and upward to find
Altair in Aquila, the star easily recognizable by its two
flanking outliers, Alshain (Beta
Aql) and Tarazed (Gamma). Look
a little bit to the northeast to find Delphinus, the Dolphin, which looks like a hand with a
finger pointing back to the southwest. On August 14, Delphinus was
found to host a modest "nova"
that just barely reached fourth
magnitude and is now not visible to the naked eye. In a nova, a
star in a double
system feeds matter through tidal
action onto a dense stellar remnant, a white dwarf. The new
surface layer eventually explodes, enormously increasing the
brightness of the system, which eventually returns to normal.
