Astronomy news for the week starting Friday, March 2, 2001.

The Moon passes through first quarter on Friday the 2nd, and will spend the week waxing toward full, that phase reached next Friday March 9, a day after it passes perigee, when it is closest to the Earth for this orbital round. For those in the Americas, first quarter will take place around the time twilight darkens the sky, the Moon just to the east of Jupiter. In the third century BC, the great Greek astronomer Aristarchus of Samos tried to estimate the distance to the Sun by observing the angle between the Moon and Sun at the time of its quarters. Only if the Sun is infinitely far away will the angle be exactly 90 degrees. His value of solar distance fell short by a factor of 20 (the Sun so far away that naked-eye measure is not possible), but his idea that the Sun was vastly farther than the Moon was correct, and vividly reveals the knowledge and intellectual vitality of the times.

The Moon is positioned this week between the group of bright evening planets -- Venus (brilliant to the west), Saturn, and Jupiter (the latter two high to the south in Taurus) -- and lonely Mars, which does not rise until nearly 1 AM. Venus makes special news by beginning its retrograde, or westerly, motion against the stars on Thursday the 7th. Since it passed greatest elongation from the Sun last January 16, the Sun has been catching up with it even though both have been moving east. The reversal in Venus's direction means that the Sun will catch it very quickly now. Each evening the planet will be lower in the sky, and it will disappear by the end of the month. But do not despair, as it will as quickly pop up in the morning sky. The planet has been exhibiting an Arctic curiosity. The Sun is still south of the celestial equator, whereas Venus is now well above it. From somewhat above the Arctic Circle, Venus sets after the Sun, as it does at lower latitudes; but it also rises shortly before the Sun, making it both a morning and evening "star."

Mars, by itself, is not left out of the picture, however. On Saturday the 4th, the red planet passes 4 degrees north of its reddish namesake Antares in Scorpius ("Antares" meaning "like Ares," "Ares" the Greek version of the god of war). The two have similar colors, are both in the Zodiac, and while Mars is now about half a magnitude brighter than the star (and brightening as well), they still look quite similar and are easily mistaken for each other.

Scorpius, beautifully placed within the Milky Way, rises roughly as Orion and his pair of hunting dogs (Canis Major and Canis Minor) set, and gives those in the northern hemisphere hope that summer is not all that far off.
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