Feb 01

February 2007

Whats Up in the Sky February, 2007

Sirus, The Dog Star

I normally do not joke around when people ask me about the stars, especially when they ask about the star Sirius.

Sirius, also known as the Scorching One or the Dog Star, is prominent in the southern sky at this time of year. Just look to the lower left of Orion and you can’t miss it shining brighter than any other star. It is so bright that some have even observed it in the daytime through a small telescope.

At 8.6 light years, Sirius is the 5th nearest star known. Among naked-eye stars, only Alpha Centauri is closer. It has more than double the suns mass and diameter and, if it were as near as the sun, it would shine over 26 times brighter.

Being the most brilliant of the fixed stars throughout history, Sirius has been an object of wonder to all ancient peoples. Similarities in the Greek, Roman, Arabic, and Egyptian names suggest a common origin from an earlier language, possibly Sanskrit.

The ancient Egyptian calendar was based on Sirius annual first appearance in the predawn sky, announcing the coming rise of the Nile.

References to the star can be found in the writings of Homer, Plutarch, and Virgil as well as in Hindu, Persian, Babylonian, and Chinese records. It is no wonder then that many myths and legends surround the star, some of which are not so old.

In the early 1800’s, observations of Sirius indicated it had an unseen companion orbiting every 50 years or so. Lost in the glare of its parent star, the companion, Sirius B, eluded observation until 1862 when it was discovered near its predicted location by Alvan G. Clark. The 18.5 inch refracting telescope he used is still in service at the Dearborn Observatory of Northwestern University.

Despite some ancient astronaut legends surrounding the African Dogon tribe’s unusual knowledge of this invisible companion, it is an intriguing object to modern astronomers. Sirius B is a white dwarf (the first to be discovered), a star with a mass about equal to that of the sun but a diameter some 40 or 50 times smaller. Thus it is incredibly dense, a cubic inch of its matter weighing over 2 tons! It also attracts material from Sirius which builds up and causes the white dwarf to heat up and eventually collapse. This triggers a new chain of nuclear reactions ending with the star exploding in what is known as a Type I supernova. Such an event, occurring so close and releasing massive amounts of radiation could have dire consequences for us. However, this probably wont happen for a million years.

So enjoy this beautiful beacon of light up in the sky, before it gets serious.

This month in history:

Feb. 1: Shuttle Columbia breaks apart during reentry killing all 7 astronauts – 2003
Feb. 4: Pluto discoverer Clyde Tombaugh born – 1906
Feb. 5: Alan Shepard hits golf balls on Moon – 1971 *
Feb. 15: Galileo Galilei born – 1564
Feb. 18: Pluto discovered – 1930
Feb. 19: Nicholas Copernicus born – 1473
Feb. 20: John Glenn is first American to orbit Earth – 1962
Feb. 24: Detection of first pulsar (by Jocelyn Bell in 1967) is announced – 1968

Here are this month’s viewing highlights:

Planets this month: Venus, in SW at dusk, climbs higher in the sky as month progresses. Mercury may be visible near Venus as month begins. Jupiter is visible before sunrise in SE. Saturn rises in the east at dusk and is visible all night.
Feb. 2: Full Moon
Feb. 10: Last-quarter Moon.
Feb. 11-12: View crescent Moon, Antares, and Jupiter close together in SSE one hour before dawn.
Feb. 17: New Moon.
Feb. 19: Venus close to crescent Moon in WSW 40 minutes after sunset.
Feb. 24: First quarter Moon.

Peter Burkey – SAAA President