SKYLIGHTS
Astronomy news for the week starting Friday, May 26, 2000.
The next Skylights will appear on Sunday, June 4. We begin this
extended week with the Moon just passing its third quarter, on
Friday, May 26. The remainder of the week sees the Moon in its
waning crescent phase, and a week later, on Friday, June 2, it will
pass new.
One of the great events of planetary alignment takes place this
week, on Wednesday, May 31, when Jupiter passes Saturn, and the two
are in their classic "Grand Conjunction." Jupiter takes 11.86
years to go around the Sun, while more distant and slower Saturn
takes 29.42 years, very close to half again as long (which is
probably no simple coincidence). Once Jupiter passes Saturn,
because of Saturn's motion, Jupiter takes 19.9 years to catch it
again, acting like a faster runner lapping a slower one on a giant
outdoor track. The last Grand Conjunction occurred some twenty
years ago, on July 30, 1981, when the two were beautifully placed
in the evening sky. This one, unfortunately, is the reverse, as
the two planets are not very well placed in morning twilight. You
will have to wait until 2020 to see another. Nevertheless, have a
look, making sure you have a good dawn horizon. The event, of
course, means nothing physically, only that two planets are in the
same direction as seen from Earth. They are at very different
distances from us, Jupiter 6 astronomical units away, Saturn 10 AU,
70 percent farther. The conjunction has no effect on anything.
The thin crescent Moon will be to the west of them the morning of
their conjunction and to the east of them the morning of Thursday,
June 1.
In the evening, Mercury is putting on a bit of a show, such as it
is for the tiny planet (though it is working as hard as it can).
It reaches greatest elongation next week and can be seen as a
rather bright "star" low in the northwest not far above the horizon
in evening twilight. The Moon passes the little planet the night
of Saturday, June 3, and will be below it (and very hard to see)
that evening, but well up and to the left of the planet the night
of Sunday, June 4.
Compared to Pluto's, Mercury's show is spectacular. The most
distant planet, visible only in substantial telescopes, will
nevertheless be at its best, reaching opposition to the Sun on
Thursday, June 1, within the confines of the constellation
Ophiuchus, which is now climbing the eastern sky around real
midnight (1 AM daylight time). Though this smallest of planets has
been known since Clyde Tombaugh discovered it in 1930, we have only
known anything of its nature in the last few years. Pluto is both
the "last planet" and the largest body of the Kuiper Belt, a disk
filled with small icy bodies that extends far beyond the planetary
system. The Belt is the origin of the short-period comets, those
that orbit in under 200 years. Pluto, a distinctly evolved body,
is apparently an accumulation of them.
