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

With "Leonid fever" at an end, at least for this year (there is still a possibility of activity next year), we look again at the more-quiet sky and at the Moon, which at the beginning of the week waxes toward full. As it goes, it passes four degrees south of Jupiter the evening of Saturday the 20th, and three degrees south of Saturn the night of Sunday the 21st. Full phase will be reached just about midnight the night of Monday the 22nd with the Moon close to the meridian to the south and set against the stars of Taurus, the Moon to the south of the Pleiades -- the "Seven Sisters" -- star cluster.

As the full Moon rises, look for the "Moon illusion," which makes the Moon look much larger on the horizon than when it is high in the sky. It is strictly an optical illusion, as the Moon has the same angular diameter at midnight, a half a degree, as it does at its rising or setting. (Constellations also look larger as they rise). In fact the Moon is angularly quite small (as anyone who has tried to take a picture of it will attest). As it passes the Pleiades, note that it could easily fit within the cluster's confines, the cluster double the angular lunar size (binoculars will help).

By the end of the week the Moon will be well within its waning gibbous phase as it rises progressively later after midnight. Less than one day after full, the Moon passes perigee, its closest point to the Earth. The coincidence will raise particularly high tides at ocean beaches throughout the world.

On Tuesday the 23rd, the Sun enters the confines of the constell ation Scorpius from Libra for the briefest of stays. Though Scorpius is famed as one of the great classical constellations of the zodiac, the Sun inhabits it for less time than any other, passing through it in a mere week. The most southerly point of the ecliptic (the winter solstice) is in Sagittarius, but Scorpius dips considerably farther to the south, and only a piece of its modern boundaries come up to meet the solar path. From Scorpius the Sun will cross over the modern boundaries of the non-zodiacal constellation Ophiuchus, in which it tarries much longer.

Directly north of the full Moon, find the brilliant autumn constellation Perseus, whose main figure consists of branching streams of stars. With the Moon out of the way later in the week, we can appreciate the density of stars at Perseus's center, the collection yet another naked-eye cluster.
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