The Perseids (August's Annual Meteor Shower)

August is upon us and that means it's time once again for the Perseid meteor shower.

Animation Credit: NASA MSFC

The Perseids are without a doubt one of the most popular meteor showers of the year for stargazers, largely due to the fact that the shower occurs in August. The peak date for the Perseids is Thursday, August 12, 2010. As the new moon for August is on the 10th this year, it should prove to be a very exciting shower. This is one of the longest meteor showers of the year, beginning July 17 and lasting until August 24. Even if your weather is unfavorable for meteor viewing on the peak date, there are plenty of chances to catch these "shooting stars" before the shower ends.

The full moon this year falls on the last day of the shower, August 24. Although a full moon will diminish meteor viewing to a slight degree, the full moon of August will be the most distant moon of the year. This distance makes the August moon the smallest of the year. Very definitely a plus for night sky watchers!

The best viewing for the Perseid meteor shower is as far from city light pollution as possible. Look to the northeast after midnight in the Northern Hemisphere. The best viewing will come in the hours closest to the dawn. The Perseids are named as such because they appear to come from the constellation Perseus, which at this time of year is just a bit to the east of the constellation Cassiopeia.

The meteors seen during the Perseid shower are actually debris left by the comet Swift-Tuttle as it continues on its 130-year orbital path around the Sun. Although the meteors appear to be fairly large to the naked eye, the debris causing them is generally about the same size as a grain of sand; however, a few may be similar in size to a marble or a pea. This stream of debris is known as the Perseid cloud and the majority of the dust within this cloud is approximately one thousand years old. There is also within this cloud a fairly new filament of dust left by Swift-Tuttle in 1862. Meteors originate from this filament at a much higher rate than from the rest of the debris stream.

Activity from the Perseid meteor shower was first recorded in the Chinese annals, which state that in the year 36 AD "more than 100 meteors flew thither in the morning". This August shower is also known as the "tears of St. Lawrence", since there is an abundance of meteors at the time of the festival in Italy for St. Lawrence on August 10.

The peak of the shower on August 12 should show, under optimal conditions, somewhere around 60 meteors per hour. The first hourly count, also called the ZHR (Zenithal Hourly Rate), was provided in 1839 by E. Heis from Münster, Germany. Lambert Adolphe Jacques Quételet of Brussels, Belgium, is credited with the actual discovery of the shower. In 1835, Quételet reported the activity that appeared to be emanating outward from the constellation Perseus.

So, grab a lawn chair or a blanket, find a nice, dark location and relax and enjoy the show! Binoculars can be helpful in locating faint meteors and tails but the best viewing is done with just your eyes. These meteors move extremely fast, traveling at speeds of up to 133,200 mph (60 kps) and many could be missed while using any visual aids.