Geology 105
Introduction to Astronomy

Timothy McDonnell - Instructor


Astronomy Puts the Universe at Your Fingertips!

Astronomy Home


Practice section

Concept of the Week


Autumn Constellations

Taurus the Bull

Taurus the Bull


Pisces the Fish


Aries  the Ram


Andromeda Galaxy

The Andromeda Galaxy (M31) is found around a 1/4 sky below Vega. It can be seen with even weak telescopes.


One of the most beautiful star clusters (the Pleiades) is found near the constellation Taurus, now visible in the last evening sky. Just below it is the planet Mars.

What's New in Astronomy 2009

1. What you can see in the sky...
Sky Sept. 16
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).

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.

Pegasus et al

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?

TrES 4
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.

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