Astronomy news for the week starting Friday, January 22, 1999.

The Moon passes its first quarter this week on Sunday the 24th just about the time it rises in daylight in the east. As it approaches the quarter the night before, it will pass a couple degrees to the south of Saturn. Two days after the quarter, it passes perigee, when it is closest to the Earth, about six percent nearer than average.

Though Jupiter is still brilliantly seen in the southwest, far above even brighter Venus (visible only in western twilight), the two planets outside Saturn's orbit are quite invisible. Neptune passes conjunction with the Sun today, Friday the 22nd, while Uranus, a bit ahead of it in orbit, will pass conjunction with the Sun early next month.

While the Moon merely makes a close pass to Saturn, it passes OVER, or occults, the bright orange star Aldebaran, an event visible from all of the US and Canada. The first magnitude star, positioned in front of the Hyades star cluster (which makes the head of Taurus the Bull), will disappear in back of the dark leading edge of the Moon the night of Thursday, the 26th (or the morning of Friday the 27th) at a time that depends on location, ranging from 2 AM CST in the southern states through 1:50 AM CST (11:50 PM Pacific Time) on a line from southern California to Maine, to 11:25 PM PST in the northwest. Before that you will be able to see the Moon approach the bright star. Try to hide the Moon behind something to make the star more visible; binoculars will help a great deal. Stars have terribly small angular diameters, so it takes the Moon a very short time to hide the star, and the disappearance will be astonishingly abrupt. The reappearance, which will be more difficult to see because of the bright lunar edge and which will take place around 2:45 AM CST in the center of the US, will not be visible in the east as the Moon will have set. Occultations such as this are important, as the disappearance time can be measured with sophisticated equipment and the star's angular diameter -- hence physical size -- can be found. Many double stars have been discovered this way as well.

If you are up to watch the occultation, look to the other side of the sky for a starlike body that looks much like Aldebaran, the reddish planet Mars, which rises at midnight and is well up in the southeast at moonset.
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