The Free Press, Mankato, MN


August 15, 2011

Starline: Vega visible in August

— Watch the sky in August as the sun sets. As it gets dark the first star you will probably see is Vega, a very bright star visible high overhead. As a result of the long-term motion of the Earth’s rotation axis, called precession, Vega, instead of Polaris, was the pole star in 12,000 B.C. and Vega will be the pole star again in 14,000 A.D. Early in August, by 11:00 p.m., when it is thoroughly dark, Vega will be almost at the zenith, the point directly overhead. The next star you might notice as the sky gets darker is the bright red star Arcturus high in the west. The light from Arcturus was used to open the 1933 Chicago World’s Fair using a photoelectric switch. This was considered appropriate because the light from Arcturus takes about 40 years to travel to the Earth and it had been 40 years since the last Chicago World’s Fair.


          Unfortunately the best meteor shower of the year, the Perseids, will be partly hidden by the light of a full moon this August. The Perseids peak late Friday, August 12 and the moon is full August 13. That will make it difficult to see faint meteors.  The Perseid meteors are produced when dust from Comet Swift-Tuttle is pulled into the Earth’s atmosphere and burns up. The Perseids produce as many as 60 meteors per hour and even if faint meteors aren’t visible there still could be a good show. Meteors will be visible all over the sky but they will radiate from the constellation Perseus which rises in the northeast about midnight. Since the full moon sets around midnight this is a good time to start observing meteors.

          If you are up at midnight looking towards the east for Perseid meteors also look for Jupiter rising just a little north of east.  Jupiter is very bright so bright moonlight can’t hide it. Astronomers learned a lot about Jupiter from the NASA Galileo space probe which reached Jupiter in 1995. This August NASA is scheduled to launch a probe named Juno to Jupiter. It will take five years to get to Jupiter and will study Jupiter close-up for a year. In the end Juno will plunge into Jupiter’s atmosphere and be destroyed to avoid any possible contamination of Jupiter’s moons. Understanding Jupiter’s structure has become even more important since hundreds of Jupiter-like planets have been discovered around other stars.

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