Skylights featured on Astronomy Picture of the Day

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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9 -- Full List Restored!


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.
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