Photo of the Week.Planet Earth: Under a brilliant
blue sky, clouds march to the edge of the southern tip of
Greenland, the huge island that holds one of the greatest glaciers
on Earth. Icebergs float in the North Atlantic just offshore. See
full resolution.
Astronomy news for the week starting Friday, October 6, 2006.
The week spans the waning of the gibbous Moon. The full
phase, with the Moon opposite the Sun, is passed on
Friday, October 6 during the evening hours before midnight in North
America.
Last quarter is then passed on Friday the 13th.
This is the season of the "Harvest Moon," which is commonly the
name of the September full Moon, but since this one is closer to
the equinox date, the October full Moon (more commonly called the
"Hunter's Moon") serves just as well. Rising nearly due east, the
Harvest Moon is caused by the eastern evening ecliptic lying rather flat against
the horizon. As a result, the delay in moonrise around the time of
full Moon is the smallest of the year, which gives us plenty of
early evening post-full-moonlight: just right for the harvests of
earlier times.
Jupiter descends even lower into the early evening sky. On
Tuesday, October 10, it passes something of a divide, setting as
astronomical twilight ends (defined as the time when the Sun
reaches 18 degrees below the horizon, and the sky becomes fully
dark). So look early to catch the "big guy," as there is little
time left before it disappears from the evening altogether. With
Mercury making a
dreadfully poor appearance in the evening sky, Venus and
Mars
completely gone to respective morning and evening twilights, that
leaves the planetary sky to morning's Saturn.
Rising around 2:30 AM Daylight Time in western Leo, the ringed planet stands due east as twilight
approaches.
While dominating the planetary sky, Saturn is
still no match for the brightest
stars. Shining at magnitude 0.5, it is quite overwhelmed by
brilliant Sirius (which in the
twilight morning sky glows to the south), and also beaten out
by Rigel in Orion (up and to the right of Sirius), by Capella in Auriga (north of Orion), and even by Procyon in Canis Minor (to the left of Orion).
Back in the evening, look into the western sky for the trio that
makes the Summer Triangle: Deneb in Cygnus (at the top of the Northern Cross), Vega in Lyra (just barely fainter than orange Arcturus, which is escaping to the
west), and Altair in Aquila. As autumn deepens, all are
reminiscent of warmer days past.
