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Skylights featured three times on Earth Science Picture of the Day: 1 , 2 , 3 , 4 .


Photo of the Week.. The Moon rides above the shadow of the Earth (projected into the atmosphere), the two setting in the west.

Astronomy news for the week starting Friday, June 18, 2004.

The Moon climbs the western evening sky this week as it waxes in its crescent phase, its nighttime side glowing with earthlight. As it moves each night farther to the east, it takes on three planets. The night of Friday the 18th, a very thin crescent will be visible in rather bright twilight just to the right of Saturn, which is becoming increasingly invisible. The following night, on Saturday the 19th, the Moon will be nicely positioned just below a line that connects the star Pollux in Gemini (to the right of the Moon) and Mars (to the left of the Moon).

By Tuesday the 22nd, the growing crescent will have entered western Leo, and on the night of Wednesday the 23rd, it will make an excellent sight just above bright Jupiter, which is about the only "ancient" planet we have left to admire, all the others pretty much gone. Venus famously passed inferior conjunction with the Sun last June 8, when it made a spectacular transit across the solar disk, and on Friday the 18th, Mercury does the opposite and goes through its superior conjunction, when it is on the other side of the Sun. Venus is now preparing its morning appearance in eastern dawn, while Mercury will in another month lay weak claim to the low western evening sky.

But now it is us, the Earth, that makes the news, as its rotation axis points to its maximum degree toward the Sun and astronomical summer begins in the northern hemisphere (winter in the southern). On the Saturday, June 20, at 7:57 PM Central Daylight Time (8:57 EDT, 6:57 MST, 5:57 PST, 3:57 Alaska-Hawaii), the Sun will cross the Summer Solstice in Gemini, as it reaches its greatest northerly extent of 23.4 degrees north of the celestial equator. At that moment the Sun will be overhead somewhere on the Tropic of Cancer (23.4 degrees north of the equator), will be as high at the Earth's North Pole as possible, and will be circumpolar at the Arctic Circle (66.6 degrees north latitude), bringing 24 hours of daylight to as much of the Earth's surface as possible, and will just barely not rise at the Antarctic Circle (66.6 degrees south). (Actually, because of refraction by the Earth's atmosphere, which raises the Sun upward, and the half-degree diameter of the Sun, the limits are a bit south of both the Circles.)

It's time for Arcturus, the zeroth magnitude star that is the brightest of the northern hemisphere, one that can be seen quite well from the southern hemisphere as well. Now on the meridian around 9 PM Daylight Time, it anchors the large constellation of Bootes, the Herdsman, which spreads northward toward the Big Dipper. To the west of Arcturus is Tau Boo (just beyond brighter Muphrid), which hosts a Jupiter-like planet, while farther to the west is Coma Berenices, a nearby cluster of stars that with a couple others makes its own constellation of the same name.
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