The Perseids 2007 - Information Guide

There is already a discussion going on in this thread , however, we are concentrating on the actual event information here. Feel free to use this information to share with your club members etc.

The Perseids, probably the most watched and studied of the regular annual showers, never fails to disappoint ground-based observers. Each year, activity from the region of sky occupied by the constellation of Perseus begins to rise from July 17th, peaks on the nights of August 11th and 12th, and begins to wane back to normal background rates by around August 23rd.

Background
The source of any meteor shower is cosmic dust - that hard to find material floating so loosely in the vacuum of space. Much of it is left behind by travelling asteroids and comets. Some of these pass through the plane of Earth's orbit. Thus, when Earth collides with one of these dust trails, these particles bombard the upper atmosphere at speeds ranging from 70,000 to 140,000 miles per hour. Earth's atmosphere is a protective blanket, which not only protects life underneath from harmful radiation such as ultraviolet, gamma rays, and infra red, but also from physical objects. These objects, while colliding into the atmosphere at such great speeds, stand little chance of surviving the trip, and burn up quickly and harmlessly in a brief, fiery display, known as a meteor. Only the largest will survive fiery entry and hit ground level, becoming known as a meteorite.

The meteors we see during the timeframe described above seem to appear, or radiate, from the constellation of Perseus, hence how they get their name “Perseids”. These meteors were once part of the comet Swift Tuttle (official designation "109/P"). The comet was discovered in 1862 by Lewis Swift and Horace Parnell Tuttle. Previous observations, but no identifications, go back to 69BC. Even though the comet takes 133 years to make one orbit around the Sun, it is large and generous enough to leave behind a thick trail of debris. Some dust trails overlap and move through space, so this year, we might pass through a trail left behind the comets 17th century pass, for example. It last passed Earth in 1992. Don't worry - there is plenty to go round!



Where to look
Perseus was the Greek hero that slain the evil Medusa, thus protecting his mother Danae from the unwanted attentions of King Polydectes as part of a bet. His form against the nightsky can be seen caught between Cassiopeia above (the ‘W’ shaped constellation), and Taurus the Bull underneath. It can be seen at its highest point at midnight in November, but during the latter half of summer will be seen rising in the northeast around 10pm local Irish time, getting higher as the night progresses. The brightest stars of Perseus make up a shape resembling the bone of a T-bone steak. It’s brightest star, Mirfak, can be spotted at the top of the ‘T’ intersection, while its second brightest star, Algol, known as the “Winkling Demon”, is the brightest star at the base. If in doubt, many sources on the internet will show you via an online star atlas where to find Perseus. As a quick find, standing outside around 10pm in August, look northeast, and you will see the ‘W’ of Cassiopeia in front of you. Following not far behind coming up from the horizon is Perseus.




Observations
Meteor observing is easy. All you really need is a comfortable chair, warm clothes, and a flask of your favourite hot beverage! Some people however, like to record their observations, either for personal posterity, or even to aid observations and studies around the world. Either way, you do not need any astronomical equipment – just your dark-adapted eyes.
This year, the Perseids favour or North American-continent friends. The maximum expected peak will be at around 6am Irish Time (5am GMT) on the morning of Monday August 13th. That only means that MAXIMUM expected rates will occur around that time. However, the high rate of activity can happen about 24 hours either side of that time, so both Sunday and Monday nights should still offer even around 30 meteors per hour for Irish observers at good observing sites. The peak average is about 60 to 70 meteors per hour from a good dark sky site. Naturally the more light pollution at your location will mean that the fainter meteors will be missed. And if it’s cloudy… well, lets not think about that! Bursts of anything up to 120 meteors an hour have been recorded in previous storms.

If you do see any, Tullamore Astronomical Society would like to hear of your observations. Send anything to tullamoreastronomy@yahoo.co.uk.

Clear Skies,

Seanie Morris.