Astronomy news for the week starting Friday, December 29, 2000.

Our Moon, Earth's ancient companion, ends the year, the century, and the millennium (technically anyway) as a growing crescent. On the second day of 2001 it will pass its first quarter amidst the dim stars of Pisces just to southeast of the Great Square of Pegasus, thereafter waxing toward full. As it moves against the starry background, it beautifully encounters the sky's brightest planet. Tonight, Friday the 29th, the earthlit crescent Moon will make a close pass to (falling just below) Venus, the modest star Deneb Algedi (Delta Capricorni) roughly between the two. The Moon will pass beneath Saturn next Friday evening, the ringed planet now shining to the east at sundown just above and to the right of brilliant Jupiter. The morning hours host only one planet now, Mars, which continues to brighten among the stars of eastern Virgo as the Earth slowly catches up with it. The red planet will not become an evening object until the beginning of April, when it finally rises before midnight.

Once again the Earth is on stage, as it passes perihelion with the Sun, when it is closest to the Sun on its elliptical orbit, on Thursday, January 4 at a distance of 147,097,500 kilometers (91,402,150 miles). Rather obviously, since the northern hemisphere is now in the dead of winter, the variation in distance from the Sun -- which is not great, only about 3.5 percent -- is not the cause of the seasons (which are produced solely by the tilt of the Earth's axis relative to the vertical to the orbital plane). Aphelion, when the Earth is farthest from the Sun, will take place this year on the United States' national holiday, the Fourth of July, when we will be 152 million kilometers (94.5 million miles) away. All things being equal, the variation in distance to the Sun should cause the Earth's southern hemisphere to have greater seasonal extremes than the northern (Argentina's summer coinciding with perihelion, winter with aphelion), but the effect is quite lost in the inequality of land masses on Earth, most of the moderating oceans being in the south.

The autumn stars, Pegasus, Aries, and the rest, begin their annual flight to the west as the winter stars take over. Orion is now up as the sky darkens. He makes his great transit across the southern meridian around 11 PM, and serves as the centerpiece for a host of bright stars and constellations that encircle him. The stars of Orion, together with those of Canis Major, Taurus, Perseus, and others, are part of a celestial ring of bright, relatively nearby stars called "Gould's Belt" (after B. A. Gould, a prominent nineteenth century astronomer) that tilts slightly relative to the Milky Way, the band of light created by the disk of our Galaxy (the portion of the Milky Way running to the east of Orion faint and difficult to see). Happy New Year to all; may it bring health, peace, and prosperity.
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