SKYLIGHTS
Astronomy news for the week starting Friday, December 1, 2000.
The Moon, beginning the week as a thick evening crescent, passes
its first quarter the night of Sunday, December 3, around the time
of moonset in the Americas, and then begins its gibbous growth
toward full. The vocabulary of astronomy is often perverse, as at
first "quarter," we see "half" the sunlit face of the Moon, the
other half in darkness. As a result, "half" and "quarter" seem to
mean the same thing. "Half," however, refers to the visibility of
the lunar disk, whereas "quarter" refers to the quartering of the
orbit, of the phase cycle of 29.5 days. From the whole cycle comes
our "month," from the quartering, at least in part, the
"week."
The week also begins with the Moon passing a couple degrees south
of the planet Uranus, now in Capricornus, and the first of the
"discovered" planets, found by William Herschel in 1781. Twice as
far from us as Saturn (which now is well up in the east at the end
of twilight, just up and to the right of bright Jupiter), and only
half Saturn's size, Uranus is only barely visible to the naked eye.
Currently a bit to the west of Uranus, and half again as far away,
30 times Earth's distance from the Sun, lies Neptune, which
requires a small amateur telescope to see. Discovered around 1846
as a result of its gravitational pull on Uranus, Neptune takes 165
years to orbit and will not complete a full turn since discovery
for another decade. Finally, at the end of the planetary system is
dim Pluto. Only about the size of the western US, Pluto averages
40 times Earth's distance from the Sun (though now it is just
beyond Neptune). With a highly tilted orbit that now places the
planet in the constellation Ophiuchus, Pluto passes conjunction
with the Sun on Monday, the 4th. The Sun, in its inexorable
apparent journey around the ecliptic will pick off Neptune and
Uranus early next year.
Pluto may be the end of the planetary system, but hardly the Solar
System. Around and beyond Pluto lie hundreds of discovered small
bodies of the "Kuiper Belt" of comets. The planets seem to have
assembled from small bodies, which in turn were created from the
accumulation of the dust that surrounded the early Sun. Pluto a
transition object, seems to have tried to match its bigger brothers
but could not quite make it as a result of the lack of raw
material.
Around 7:15 PM, the "equinoctial colure," the north-south-circle
that connects the equinoxes and the poles, rides the celestial
meridian. Looking to the south from North America, the colure is
bracketed by two lonely stars. To the west of the meridian find
first magnitude Fomalhaut in Picsis Austrinus, the Southern Fish,
while to the east lies second magnitude Deneb Kaitos, which marks
the tail of Cetus the Whale, within a "wet" section of sky that
includes Delphinus, Capricornus, Aquarius, and Pisces.
