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


Photo of the Week. Cygnus and the Northern Cross stretch from bright Deneb, near center, down and to the left through Sadr (Gamma Cygni), along which runs the summer Milky Way. North is to the right. See full resolution and identifications.

Astronomy news for the week starting Friday, June 17, 2011.

In its perpetual rounding of Earth, and having passed full phase last week (when it survived yet another total eclipse), the Moon spends the early part of our week in the waning gibbous phase, not going through its third quarter until the morning of Thursday, June 23, when from North America you can see the near- perfect quarter to the south at dawn. It then slips into the waning crescent phase. On the evening of Monday the 20th, the Moon swings six degrees north of Neptune (the rather large angle the result of the Moon's orbital tilt taking it north of the ecliptic), while during the night after third quarter it similarly takes on Uranus (both the planet and the Moon near the Vernal Equinox in Pisces). The night of Thursday the 23rd the Moon finishes the week by going through its apogee, where it is farthest from the Earth.

Having passed the meridian well before sunset, Saturn is now firmly into the southwest as the sky darkens, and still to the northwest of Spica in Virgo. Setting ever earlier, the planet is now gone by 1:30 AM Daylight Time. Only half an hour after Saturn's disappearance, though, Jupiter makes its jump over the eastern horizon, the planet now near the Pisces-Aries border. The first in a line of three, Jupiter leads (and is pulling away from) Mars, which now rises close to the Aries-Taurus boundary as dawn begins to light the sky. Venus, moving oppositely to these two relative to the Sun, continues to lose ground, not rising until mid-twilight.

The big event, though, involves Earth, as at 12:16 PM Central Daylight Time on Tuesday the 21st (1:16 EDT, 11:16 AM MDT, 10:16 PDT, etc.), the Sun passes across the Summer Solstice (which is close to the line that formally separates Gemini from Taurus), marking the beginning of northern hemisphere astronomical summer. On that day, the Sun (at its maximum angle of 23.4 degrees north of the celestial equator) rises and sets as far to the north of east and west possible, is up for the maximum number of hours (giving us the year's two shortest nights), is overhead at the Tropic of Cancer (23.4 degrees north latitude), and is as high as possible at noon for anyone to the north of that circle (and as high as possible all day at the north pole). For the next six months after, the Sun will be moving toward the south and Winter Solstice passage next December.

Look for Arcturus, the brightest star of the northern hemisphere, high to the south as the sky darkens. Then plunge far southward to see the stars of northern Centaurus, the classical Centaur, as they glide above the southern horizon. From north of 50 degrees north latitude, they are lost, while from the Tropics you can also see Centaurus's luminary, Alpha Cen, as well as the Southern Cross to the west of it, with bright Beta Cen in between.
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