During the months of September and most
of October, the summer sky gradually changes to show off the stars
of autumn. The most prominent planet in the autumn
evening sky is
the giant
Jupiter. It is easily located in the southern part of
the sky, just as the sky gets dark. This year it sits in the middle of Capricornis,
the "Goat."
. On Sept. 20 and Oct. 26, you will see Jupiter next to
a nearly-full moon.Through a telescope you should be able to find Jupiter's
four
Galilean Satellites. These moons were shown
by Galileo to revolve around Jupiter, and it helped him to prove the heliocentric
(sun-centered) universe.
In mid September 2008, an interesting event will occur in the western sky
just before sunrise.
Venus, the
Moon, and the bright star
Regulus will form a triangle just above the horizon. (see picture
above). This will happen in the constellation
Leo the Lion. As the
month progresses,
Venus will catch up with
Saturn, with faint
Mercury nearby. If you follow Venus into October, you will see her move
into the constellation
Virgo, leaving Saturn far behind. Now you know
why the Greeks called them
planets (or "wanderers).
CONSTELLATIONS: The summer triangle (made by connected the bright
stars
Vega, Deneb, and
Altair) is still visible but
it is slowly falling into the western sky. Now dominating the northeastern
sky is a quartet of constellations rich in Greek mythology:
Cassiopeia
(the Queen),
Andromeda (the Princess),
Pegasus
(the winged horse), and
Perseus (the hero who killed Medusa).
In Pegasus you easily find the asterism called "The Great Square,"
which also includes the face of Andromeda. Not to be outdone, the Princess
hosts a fuzzy patch near her left knee. When viewed through a telescope,
it is the huge galaxy also called
Andromeda. Perseus is easier to
see around midnight. In his right leg is the star
Algol, which
varies in magnitude, indicating that it is entering the last stages of
its life.
2. What's New in the Solar System?
The biggest controversy in astronomy came out of a meeting of the
International Astronomical Union in 2006 where they decided to update the
definition of the word "planet." A planet must be round, orbit near the plane
of the Solar System directly around the Sun, and it must "have cleared its
neighborhood." In 2008, they adopted a new classification called the
plutoid. This refers to Pluto-like dwarf planets
beyond Neptune. This includes
Makemake, a plutoid between the orbits
of Pluto and Eris.
Watch the news! This new definition is going to have result in more
changes in the Solar System.
Ceres is a dwarf planet found in the
asteroid belt. What is it doing there?
Planets have also been discovered
beyond our Solar System. Recently a very large extrasolar planet (called
TrES 4) was found revolving around a star in the
constellation Hercules. It is about 70% larger than Jupiter, and very close
to its host star - just 4.5 million miles away, a tenth of an AU! That means
its period of revolution is just 3.5 days. It probably is a gaseous planet,
so the powerful gravitational forces must cause it to have a tail, like a
comet.
The picture you see here is just an artists conception, of course.
