Photo of the Week. The famed
Barringer Crater ("Meteor Crater") near Winslow Arizona (USA)
is an impact site three-quarters of a mile across and 600 feet
deep, made 50,000 years ago by a house-sized nickel-iron asteroid.
As big as it is, it pales beside others like Manicouagan. (See it at
full resolution.)
Astronomy news for the week starting Friday, September 8, 2006.
The sky is quiet this week as summer draws toward its end. The
Moon is now running through the back half of its journey around the
Earth. Spending the week in the waning gibbous phase, it passes through third
quarter at week's end on Thursday the 14th. With the Sun
approaching the autumnal equinox
in Virgo, the third
quarter, 270 degrees around the orbit from new, will be high
along the ecliptic
approaching the summer solstice in
Gemini/Taurus. Watch for it making a fine appearance above Orion, which even though it is still
summer is giving us a glimpse of the coming winter. The Moon
begins the week near perigee,
where it is closest to the
Earth.
As the
seasons change (though autumn does not formally begin until
September 22), it hardly seems possible that summer is actually
three or so days longer than winter (and spring longer than fall).
The origin for this "inequality of the seasons" (known since
ancient times) is the eccentricity of the Earth's orbit. We are
closest to the Sun in
early winter, which causes the Earth to move faster in orbit and
thereby to hustle through the colder months. Southern hemisphere
residents see the opposite effect.
Jupiter (in Libra) still
dominates evening, though not by much. Look for the giant planet
in the southwest in late twilight. By 9:30 or so, it is gone,
leaving the evening sky planetless except for the three faint outer
ones: Uranus
(in Aquarius), Neptune
(in Capricornus), and Pluto
(near the Ophiuchus-Serpens-Sagittarius boundary). News has it
that the planetary
research community is not at all happy with the International Astronomical Union's
decision to send Pluto to the minors, so for now let's keep it as
a real planet. The morning sky is still graced by Venus, but again not
by much, since the bright "morning star" does not rise until mid-
twilight, around 5:30 AM.
Saturn, however, now rises around 4 AM, well before dawn's
onset. Moving eastward, the ringed planet is now passing from Cancer into Leo.
The early evening sky still contains one the grandest of
constellations, Scorpius, which
dips very low to the southern horizon. Look for Antares -- Alpha Scorpii -- rather
well to the left of Jupiter. Above Scorpius is a stack of large
constellations that begins with Ophiuchus, then goes through Hercules and Draco,
finally ending at Polaris.
