Skylights featured on Astronomy Picture of the Day

Scout Report Selection Webivore Selection SpaceCareers Selection

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

Orion and Trees

Photo of the Week.. In memory of the past winter, Orion and his hunting dog Canis Major stalk the skies beyond leafless trees.

Astronomy news for short week starting Friday, April 4, 2003.

Skylights now resumes its normal schedule. The Moon passes through its first quarter this week, the night of Wednesday the 9th just about the time of sunset in North America, giving us a splendid view of this phase set on the meridian to the south. In the third century BC, the great ancient Greek astronomer Aristarchus tried to determine the distance of the Sun relative to the Moon by measuring the exact angle between them when the Moon came just to first quarter. It would be a right angle if the Sun were infinitely far away, less if it were not. From his estimate of 87 degrees, he said the Sun was 20 times the lunar distance. Though the true value is 400, Aristarchus' method was ingenious, and the result was correct in that he found the Sun notably farther than the Moon. The actual value (which was still off some) was not known until the 17th century.

As the Moon heads toward first quarter in eastern Gemini, it passes northeast of Saturn the night of Monday the 7th, and then after the quarter it swings four degrees north of Jupiter the night Thursday, the 10th. Both these outer planets, which share so much in their physical natures, are now in direct motion to the east against the background stars. Saturn, in eastern Taurus, now sets around midnight, while Jupiter, in eastern Cancer (one of the dimmer constellations of the Zodiac), is high to the sky to the south as twilight ends.

The morning sky sees Venus getting ever closer to the horizon, as the planet now rises shortly after twilight begins. Nevertheless, it is glorious in the morning southeastern sky. Rather far to the west of Venus rides reddish Mars just to the northeast of the "Little Milk Dipper" in Sagittarius.

Within the set of "modern" constellations, invented between 1600 and 1800, are a variety of navigational tools: Sextans (the Sextant), Octans (the Octant), and Quadrans (the Quadrant). Octans surrounds the South Celestial Pole, while Quadrans, no longer recognized as a formal constellation, lies near the Big Dipper (and is the "source" of the Quadrantid meteor shower, which hits on January 4th). Sextans, still viable, lies just to the south of Leo the Lion. Simply go south of Regulus (the Alpha Star in Leo) to find a triangle of faint stars, Alpha and Beta Sextantis lying on a line almost exactly parallel to the celestial equator.

Valid HTML 4.0!