Astronomy news for the week starting Friday, March 10, 2000.
The next Skylights will appear Sunday, March 19. During this
extended Skylights period, the Moon will pass through first quarter
the night of Sunday, the 12th, just around the time of moonset in
North America, and then wax through its gibbous phase toward full.
With the Sun near the vernal equinox, the third quarter will appear
near the summer solstice in Gemini, making it the highest, and
earliest rising, first quarter of the year. (Observers in the
southern hemisphere will see the reverse, the lowest first
quarter.) Confusing to beginners, "quarter moon" refers to the
same lunar aspect as "half moon." The terms mean different things,
however; "half moon" refers to the lunar appearance (half the lunar
disk in sunlight), while "quarter moon" refers to the quartering of
the orbit. Full Moon, opposite the Sun, is therefore "second
quarter," though the term is never actually used. The Moon begins
our week up and to the left of Saturn, then plows through the stars
of Taurus, the night of Sunday the 12th appearing to the east of
The morning of Wednesday, the 15th, sees little Mercury in
conjunction with its much brighter sister planet, Venus. The two
are now so low in the morning twilight southeastern sky, however,
that only Venus will be readily visible. Even Venus will not be
visible for too much longer as it steadily descends into sunlight.
The day before, the waxing Moon passes perigee, when it is closest
to the Earth.
The evening sky still revels in brightness, great Jupiter shining
in the west, dimmer Saturn up and to the left of it, and Orion and
its companions swinging to the west of the celestial meridian (the
sky's north-south line). Between the evening and morning, Pluto,
lying far above the ecliptic among the stars of southern Ophiuchus,
begins its western retrograde motion, though not many will watch,
as the littlest of planets is 800 times fainter than the human eye
can see without a telescope. Only about the size of the collected
western states, and 30 times farther from the Sun than Earth, Pluto
sends very little light back to us. So little sunlight heats it
that the temperature at best is a chilly -387 degrees F (40
centigrade degrees above absolute zero). It is so cold that some
of its very thin atmosphere falls to the ground as a snow made of
frozen nitrogen, carbon monoxide, and methane. Very similar to
Neptune's large Moon Triton, which orbits Neptune backwards and is
almost certainly a captured body, Pluto is caught by Neptune as
well, orbiting the Sun twice for every three of Neptune's years.