Astronomy news for the week starting Friday, July 17, 2009.
We begin the week with the Moon in its waning crescent phase as it
heads towards new on Tuesday, July 21. It will first become easily
visible as a western-sky waxing crescent
the twilit evening of Thursday the 23rd. The day of new Moon also
sees the Moon passing through perigee, where
it is closest to the Earth.
We also begin with the waning crescent within a glorious setting of
planets. The morning of Saturday the 18th, the Moon will make a
beautiful triangle with the Taurus's Pleiades
and Mars
, the Moon down and to the left of the cluster and just up and
to the left of the red planet. Below them both will be brilliant
Venus, and to the right of Venus (and below Mars), the Hyades cluster with Aldebaran (which is not part of
the cluster). Note both the similarity in, and the slight
difference between, the colors of Mars and Aldebaran. By the
following morning, that of Sunday the 19th, the Moon will have
shifted down and to the left, and will appear directly left of
Venus and to the right of Elnath
(Beta Tauri), the star that makes the western horn of the celestial
Bull.
New Moon and perigee combine to produce a magnificent
total eclipse of the Sun on Tuesday the 21st. (If the Moon is
closer to apogee, it is too far away to fully cover the solar disk
and we get an "annular" eclipse.)
Unfortunately, it's not for us. The path of totality, the full
shadow of the Moon, will pass across northern India and southern
China then out into the mid-Pacific Ocean. The partial eclipse
(the Moon taking a bite out of the Sun) covers much of Asia, but
Europe and the Americas will be left out entirely as, for these
lands, new Moon occurs at night.
Back to the morning sky. Mars rises ever earlier, and is now up
(moving between the Pleiades and Hyades, as noted above) by 2 AM or
so Daylight Time. Less than an hour later, up comes Venus, which
is now rising about as early as possible during this orbital round.
Though beginning to rise later, Venus will be visible during most
of the rest of the year. While the morning holds the two planets
that bracket the Earth, the evening is now the domain of the two
giants. Jupiter
unmistakably rises in the southeast in late evening twilight, about
an hour before Saturn sets in
the west.
With the Moon dimmed out, we can take an evening look at the
fainter constellations. About
three-fifths of the way from orange Arcturus (to the south of the
handle of the Big Dipper) to
bright white Vega (nearly overhead
and to the northeast of Arcturus), find the box that makes the
"Keystone" of Hercules, the rest of
the constellation seen to the north and south of it. Directly
south, above reddish Antares (of
Scorpius), is the huge distorted
pentagon that makes Ophiuchus,
the Serpent Bearer, the giant snake depicted by two streams of
stars the run to his left and right. Serpens is the only
constellation that comes in two parts.
