Feb 01

February 2006

Whats Up in the Sky February, 2006

The excitement of discovering new planets

There has been much in the news lately about the discovery of new planets, both in our own solar system and orbiting other stars. Since Saturday is the birthday of Clyde Tombaugh, the discoverer of Pluto, I thought it would be fun to recap the history of planetary discoveries.

The five brightest planets, Mercury, Venus, Mars, Jupiter, and Saturn, were known to ancient people because, unlike the fixed stars that make up the constellations, these objects changed their positions over days and weeks, “wandering” through a narrow band of the sky known as the zodiac. (The word “planet” comes from the Greek for “wanderer”.) Of course, the true nature of these objects was not known until the dawn of the scientific revolution when guys such as Copernicus and Galileo argued that they were objects like the earth, orbiting the sun.

Then, in 1781, William Herschel, an astronomer known at the time to be a skilled comet hunter, discovered Uranus by accident while searching for comets. During the next several decades, discrepancies in its orbit were observed. These could be explained by the gravitational tug of another planet nearby. Through calculations based on gravitational theory, the location of this object was predicted. Based on these predictions, astronomers observed and identified Neptune in 1846.

In February, 1930, Clyde Tombaugh, comparing photographs made the previous month at the Lowell observatory in Arizona, found an object that was soon identified as the planet Pluto.

Things remained unchanged until recently, when several other Pluto-like objects were discovered. The debate over whether we have a tenth planet continues.

Since 1995, about 160 planets have been discovered orbiting other stars. Most of these are giants, but recently an Earth-sized exoplanet has been discovered.

Our view of the planets has certainly changed dramatically from godlike objects to natural results of star-forming activity, common among the stuff we observe up in the sky.

Here are February’s viewing highlights:

Planets this month: See three planets at dusk — Mercury low in the west, Mars high in the south, below the Pleiades, Saturn rising in the southwest; Venus shines brilliantly in predawn sky, Jupiter, second in brightness

February 1: One hour before sunrise, Venus-Jupiter-Saturn span 157 degrees, from east to west
February 5: First-quarter Moon (1:29 a.m.)
February 5: Moon, just past first quarter, makes beautiful grouping with Mars and the Pleiades high in south
February 9: Waxing gibbous Moon passes between the stars Castor and Pollux and Saturn
February 12: Full Moon – most distant of year
February 14: Venus and Jupiter bright in morning twilight.
February 21: Third-quarter Moon
February 23: Crescent moon between Venus and Jupiter before sunrise.
February 23: Mercury at greatest separation from sun; look near western horizon around 7:00 p.m.
February 27: New Moon – closest moon of the year

Peter Burkey – SAAA President