Skylights featured on Astronomy Picture of the Day

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Skylights featured on Earth Science Picture of the Day: 1 , 2 , 3 , 4 , 5 , 6 , 7

Mars in Taurus

Photo of the Week. Mars (just below center) passes through central Taurus in late August, 2007. Compare the color with Aldebaran down and to the right. Aldebaran lies in front of the vee-shaped Hyades cluster; the Pleiades shine near the upper right-hand corner.

Astronomy news for the two-week period starting Friday, September 21, 2007.

Skylights will next appear on October 5, 2007.

The Moon begins our fortnight in the waxing gibbous phase, passing full on Wednesday, September 26. It then wanes through gibbous to its third quarter, which is reached almost at the end of our period, on Wednesday, October 3. As it treads its way through the Zodiac, it passes south of Neptune on Sunday the 23rd and north of Uranus two days later (both passages quite invisible to the eye). The Moon then glides 5 degrees north of Mars during the day (for North America) on Tuesday the 2nd. The night of October 1st, the Moon will thus shine to the northwest of Mars, while the following night it will have moved to the northeast of the red planet.

Two grand events take place on the same day. The first is the passage of the Sun across the autumnal equinox in Virgo at 4:51 AM Central Daylight Time on Saturday the 23rd, when astronomical autumn begins in the northern hemisphere. (Add an hour for eastern time, subtract one for Mountain, two for PDT.) Barring the effects of atmospheric refraction and the half-degree solar diameter, the Sun will rise due east, set due west, be up for 12 hours, and down for 12 hours. It will then also pass overhead at the Earth's equator, formally set at the north pole, and rise at the south pole.

Thirteen hours later, Venus reaches its greatest brilliancy for this current morning appearance. Rising now around 3:30 AM and glorious in the eastern morning sky as twilight begins, the planet is 20 times brighter than the brightest star, Sirius, which gleams in the southeast well off to the right of Venus. Through the telescope, Venus -- still more or less between us and the Sun -- appears as a large thin crescent. Rising an hour or so before Venus (less during the latter part of our period), you can then spot Saturn to the south of the Sickle of Leo and to the east of Regulus.

The early evening sky remains graced by Jupiter. Above Antares, the giant planet now sets around 10 PM. In between Jupiter and Venus is Mars, which rises in eastern Taurus about an hour after Jupiter goes down. A dedicated observer with binoculars might even spot little Mercury in western evening twilight. The planet reaches greatest eastern elongation on Saturday the 29th, though with the ecliptic fairly flat against the horizon, the view will be poor. It passes a mere tenth of a degree to the north of the star Spica on Saturday the 22nd.

Some constellations and informal asterisms just jump out at you. Good examples abound, and include the Big Dipper, Orion, Taurus, and many others that were known to the ancients. Others, those invented in more modern times, can be hard to find, some so much that one wonders what was in the minds of the inventors. Try for example to locate Telescopium (the Telescope) far south of Sagittarius and Corona Australis. Even harder to find is Microscopium (the Microscope), whose dim stars sprawl south of Capricornus. A little later in the evening then look for Sculptor (the Sculptor's Studio) immediately to the east of Fomalhaut, the bright southern star that announces the beginning of fall.
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