Astronomy news for the week starting Friday, March 19, 1999.

The Moon will be in its waxing crescent phase the early part of the week as it grows through first quarter on Wednesday the 24th, that night rising just slightly gibbous. It, Venus, and Saturn play tag with each other, the outcome quite predictable. As the two planets draw closer, the Moon will pass just below the planetary pair the night of Friday, the 19th, the three making a glorious triangle in western twilight. Venus and Saturn then make their closest pass to each other, with brilliant Venus standing three degrees to the north of much more distant Saturn on Saturday the 20th. They will be closest during mid-afternoon in North America, but there will be little difference by the time they are visible, that night the Moon well up and to the left of the planets. The Moon also plays tag with Aldebaran, occulting (passing over) it on Monday the 22nd, the event visible in Europe and the Middle East.

Jupiter is too deep into twilight to be seen, setting only half an hour after the Sun, and Mercury is completely out of the action, as it passes inferior conjunction with the Sun (between us and the Sun) on Friday, the 19th. At such inferior conjunctions, Mercury and Venus almost always pass above or below the Sun. This year is special however, as on November 15 inferior conjunction occurs just as Mercury is crossing the ecliptic path, allowing us to witness a "transit" of Mercury and to watch it actually crawl slowly across the solar disk (for safety, observed by projection with the telescope only!). Transits of Mercury take place in May and November in 7 and 14 year cycles. Transits of Venus are much rarer, the last taking place in 1882, the next not until 2004, the twentieth century devoid of them.

The week's biggest event is the passage of the Sun across the vernal equinox in Pisces at 7:46 PM Central Time on Saturday, March 20 (the event celebrated by the conjunction of Venus and Saturn!), or 01 hours 46 minutes Greenwich Time, Sunday, March 21, marking the beginning of astronomical spring in the northern hemisphere and of astronomical autumn in the southern. At that moment, the Sun crosses the celestial equator and passes into the northern celestial hemisphere. The Earth's axis will be perpendicular to the direction to the Sun, the Sun will rise due east and set due west, will pass overhead at the Earth's equator, and the days and nights will be of approximately equal length. In fact, the day will be a few minutes longer than the night because the Sun is a disk rather than a point and because refraction by the Earth's atmosphere at sunrise and sunset raises the Sun about half a degree above its actual position.
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