SKYLIGHTS
Astronomy news for the week starting Friday, May 18, 2001.
Our Moon passes through its new phase this week on Tuesday, the
22nd. Watch as the waning morning crescent, seen in eastern dawn,
thins early in the week and then appears on the other side of the
Sun to the west the evening of Thursday, the 24th. The morning of
Saturday the 19th, the Moon will appear a few degrees to the south
of brilliant Venus.
Saturn is now gone, lost to evening twilight, and Jupiter, just a
little behind, is quite difficult to find, as it now sets just a
bit over an hour after the Sun. The evening sky does present us
with a fine apparition of Mercury, however. Only a day before the
Moon passes new (on Monday the 21st), the little planet, the one
closest to the Sun, passes its greatest eastern elongation, when it
is 22 degrees to the east of the Sun and maximally visible. For
those in North America, the Moon will provide a fine guide, as the
lunar crescent will be just a few degrees to the right of the
planet the night of Thursday, the 24th. Look in bright twilight
and follow the Moon as it sets and the sky darkens to see Mercury
emerge from the fading glow. The planet remains mysterious. Of
the nine planets, only Pluto is smaller. Not quite 40 percent the
size of Earth, Mercury has the largest iron core relative to its
size of any of them. Dangerously close to the Sun, it has been
visited by but one spacecraft (Mariner 10 passing it 3 times in
1974 and 1975), and only about half has been imaged. So close in
angle to the Sun that it is visible only in the daytime or in
twilight, surface features are nearly impossible to see from
Earth.
Once Mercury sets, the evening sky awaits the rising of Mars, which
climbs above the southwestern horizon around 10:30 PM Daylight
Time. Now moving retrograde in far western Sagittarius, the red
planet, fourth from the Sun, and the last of the "terrestrial
planets" (those constructed like Earth), will be rising in evening
twilight by the end of the month.
In the early evening, for those in mid-northern latitudes, look out
perpendicular to the plane of our Galaxy. The Milky Way is about
as absent as it can get, and lies around the horizon where it is
invisible. Our view is unobstructed by the dust in the Galactic
plane, allowing us to see outward as far as our instruments will
carry us, to distant galaxies billions of light years away. From
the southern hemisphere, however, the Milky Circle is high and
spectacular as it passes through Centaurus and Crux, the Southern
Cross.
