SKYLIGHTS

Astronomy news for the week starting Friday, December 8, 2000.

The Moon begins the week by waxing toward full, the phase reached early in the morning of Monday the 11th (in the Americas). The night of Sunday the 10th, it will therefore rise just short of full just before sunset. It then spends the rest of the week waning toward next week's third quarter.

A day and a half after the Moon passes full, it passes perigee, when it is closest to the Earth. At perigee, the Moon is 5.5 percent closer than average and 11 percent closer than when it is at apogee, and therefore respectively appears 5.5 and 11 percent larger. The effect is too small to be readily visible to the eye. (That the rising or setting full Moon appears larger than normal is but an illusion). Since the apparent area of the lunar surface depends on the square of the angular size, the Moon appears almost 25 percent brighter at perigee than at apogee, making this full Moon the second brightest of the year (exceeded only by last January's). The Moon's high winter altitude at midnight will enhance the effect. The coincidence of the full phase, perigee, and the coming perihelion of the Earth next month (when the Earth comes closest to the Sun) will raise especially high tides at the coasts.

Since both Saturn and Jupiter are now past opposition with the Sun, the Moon will pass them both before it reaches its full phase. The night of Friday the 8th finds the Moon, Saturn, and Jupiter stretching out in a nice line in the east after sundown. The night of Saturday the 9th, the nearly full Moon will be between the two planets and just below the line that connects them, all this celestial activity taking place among the stars of Taurus, which the bright lunar light will make difficult to see.

Planetary conjunctions can produce dramatic beauty, as witnessed by the current closeness of Jupiter and Saturn. A conjunction on Monday the 11th is an extreme reverse example, in which the brightest planet, Venus, passes three degrees to the south of the dimmest of the major planets (discounting Pluto), Neptune. Don't bother calling the neighbors out to watch.

Though winter approaches, there is still time to say goodby to the constellations of summer. Look to the northwest to find the northern stars of the Summer Triangle, bright Vega in Lyra, and Deneb at the top of the Northern Cross, which in the early evening is standing nearly vertically. Along with them, farewell to their companions, Aquila, Delphinus, Sagitta, even dim Vulpecula. If on the other hand you wish to anticipate spring (skipping winter altogether), wait until the morning hours, when winter's Orion has passed the meridian, and appreciate spring's Leo, which will be nicely rising in the east.