Photo of the Week. Sunset. The color change from top
to bottom reflects the thickening of the Earth's absorbing
atmosphere, through which the sunlight must pass; the oval shape is the
result of atmospheric refraction that diminishes with angle above
the horizon. Watch the Sun
get lower then lower still, the Sun not dropping straight down but
descending at an angle to the right.
Astronomy news for the week starting Friday, September 9, 2011.
We begin, as always, with our Moon, which, starting off as a fat waxing gibbous, brightens to full the night of Sunday, September 11 (the
phase actually reached the morning of Monday the 12th between
midnight and dawn depending on where you live). The Moon will then
rise the night of the 11th just before sunset and the following
morning will set just after sunrise. It then spends the remainder
of the week as a waning gibbous. This
full Moon, the "Harvest Moon," is special, as with the ecliptic (the plane of the Solar
System) at its flattest against the evening eastern horizon, the
delay in Moonrise from one night to the next is minimized, giving
us lots of early evening moonlight.
The full Moon sort of splits Neptune and Uranus, not that it matters much with
the sky swamped with Moonlight. On Saturday the 10th, the Moon
passes 6 degrees north of the former, then on Tuesday the 13th
glides the same angle to the north of the latter, both events
taking place during daylight, the rather wide angle caused by the
tilt of the lunar orbit.
For a better sight, you can admire the Moon to the northwest of Jupiter the
night of Thursday the 15th. Three days after full, our Moon then
goes through apogee, where it
is farthest from Earth on its modestly elliptical orbit.
Of the five "ancient" planets, those known since antiquity, only
Jupiter and Mars make any
impact on the nighttime sky. The others are too close to the Sun for ready
viewing. Jupiter, rising by 9:30 PM Daylight Time, just after the
closing of twilight, makes the biggest impact on the nightly sky.
Up the rest of the night, the giant planet makes a striking sight
in dawn's light high in the sky just past the meridian, moving slowly easterly against
the stars of southern Aries.
Then around 2 AM, up comes
Mars. Moving eastward faster than Jupiter (as a result of its
closeness), the red planet now resides in eastern Gemini, passing six degrees south
of Pollux the night of Friday the
9th. By the end of the week, it is almost pointed to by Pollux and
Castor, Mars's brightness falling
between the two. At the other end of the visibility scale, Pluto
ceases its tiny westerly
retrograde motion on the morning of Friday the 16th, and begins
creeping eastward against the crowds of Milky Way stars in northwestern Sagittarius just a few degrees
northeast of the Winter
Solstice.
As the sky darkens, Sagittarius crosses the southern meridian, Scorpius and Antares to the west. Hovering above
the Scorpion to the southwest is giant Ophiuchus, the Serpent Bearer, which slowly emerges as
the Moon gets out of the way. Look for his luminary, Rasalhague (Alpha Oph) midway
between Arcturus and Altair.
