SKYLIGHTS
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.
