The Perseids are coming!

July and August meteor alert! Rain showers are typical this time of year but there is a different type of Cosmic shower on view less than one hundred miles above the Earth. As always, the best time to watch summer meteors will begin in late July and run through about mid-August. The Perseids is the name of a prolific meteor shower associated with the comet Swift-Tuttle and every year in August, the Earth passes through a cloud of rock and dust fragments left behind by the comet.  

Comet Swift-Tuttle (formally designated as 109P/Swift-Tuttle) is a comet that was independently discovered by Lewis Swift on July 16, 1862 and by Horace Parnell Tuttle on July 19, 1862. It’s solid nucleus is about 27 kilometers (16.8 miles) across, considerably larger than the 10-km K-T impactor object hypothesized to have wiped out the dinosaurs. The last time it came near the Sun was in 1992 on its 130 year voyage around the Sun. Most of the dust in the cloud today is around a thousand years old. However, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1862. The rate of meteors originating from this filament is much higher than for the older part of the stream.

The Perseids are so-called because the point they appear to come from, called the radiant, lies in the constellation Perseus and have been observed for about 2000 years, with the earliest information on this meteor shower coming from the Chinese in 69 BC and AD 188. Some people refer to the Perseids as the "tears of St. Lawrence", since August 10 is the date of that saint's martyrdom. The shower is visible from July 23rd, with the peak in activity being between August 12th and 14^th. And when we say August 12 or 13, we mean the morning hours after midnight.

But you don’t need to know Perseus to watch the shower. The meteors appear in all parts of the sky. The Perseids are considered by many people to be the year’s best shower, and often peak at 50 or more meteors per hour. 2010 is a great year for the Perseids. This year, the slender waxing crescent moon will set at early evening, leaving a dark sky for this year’s Perseid show. The Perseids tend to strengthen in number as late night deepens into midnight, and typically produce the most meteors in the early hours before dawn

What equipment do you need to observe the meteor shower?

The good news is none! Just use your eyes. It will help your observation if you give your eyes some time (say 15 minutes), to become adapted to the darkness. Going by this weather an umbrella might be handy too

Potential threat to Earth?

Comet Swift-Tuttle has been described as "the single most dangerous object known to humanity”. The comet is on an orbit which puts it close to the Earth and the Moon and given the size of the nucleus of Swift-Tuttle, this is of some concern. Subsequent observations have led to recalculation of its orbit, which indicates the comet's orbit is very stable, and that there is absolutely no threat over the next two thousand years. Astronomers believe that in the 2126 pass it will likely be a great naked-eye comet like Hale-Bopp. Although close encounter with Earth in the year 4479 may result in an impact at a velocity of 60 km/sec, leading to an estimated impact energy of 27 times that of the K-T impactor.

GAC Observing Session 

An informal gathering may take place weather permitting outside the city, possibly near Spiddal on or around the time of peak activity. Keep an eye out on our Forum for further updates, members will be updated via text message.

GAC member and Solar imaging expert Dave Gradwell has sent this excellent image of a large Prominence extending out from the Sun taken recently from his back garden in Portuma. Earth to scale.

A Prominence is a large, bright feature extending outward from the Sun's surface, often in a loop shape. Prominences are anchored to the Sun's surface in the photosphere, and extend outwards into the Sun's corona.

While the corona consists of extremely hot ionized gases, known as plasma, prominences contain much cooler plasma. A typical prominence extends over many thousands of kilometers and the mass contained within a prominence is typically on the order of 100 billion tonnes of material.

For more spectacular images from Dave go to www.davegradwell.com