Every year in mid-August, the Perseid meteor shower has its peak. Meteors -- colloquially known as “shooting stars” -- are caused by pieces of cosmic debris entering Earth’s atmosphere at high velocity, leaving a trail of glowing gases. Most of the particles that cause meteors are smaller than a grain of sand and usually disintegrate in the atmosphere, only rarely reaching the Earth’s surface as a meteorite. The Perseid shower takes place as the Earth moves through the stream of debris left behind by Comet Swift-Tuttle. Despite the Perseids being best visible in the northern hemisphere, due to the path of Comet Swift-Tuttle's orbit, the shower was also spotted from the exceptionally dark skies over ESO’s Paranal Observatory in Chile. In order not to miss any meteors in the display, ESO Photo Ambassador Stéphane Guisard set up three cameras to take continuous time-lapse pictures on the platform of the Very Large Telescope (VLT) during the nights of August 12-14, 2010. This handpicked photograph, from the night of August 13-14, was one of Guisard’s 8000 individual exposures and shows one of the brightest meteors captured. The scene is lit by the reddened light of the setting Moon outside the left of the frame. [Stéphane Guisard, European Southern Observatory, photo]
On the night of Saturday, August 11 and well into the next day, Earth will be at the peak of its annual passage through the bulk of the debris shed by a comet known as Swift-Tuttle. Much of the debris is composed of dust-sized grains, but when these fragments come plunging into our atmosphere they can create a dazzling meteor display. Not only are the meteors fascinating to watch, they also leave short-lived streams of ionized gas in their wake. As hams have known for years, these meteor trails are excellent reflectors of radio waves. The Swift-Tuttle meteor showers are known as the Perseids because they appear to come from a point in the sky that lies within the constellation Perseus.
This year’s Perseid meteor shower occurs when the Moon is at a waning crescent phase, which means bright moonlight won’t diminish the number of visible meteors. According to Spacedex.com., the lack of bright moonlight means that the fainter meteors should not be concealed from view: "It is advisable to observe the meteor shower during the predawn hours on the mornings of August 11, 12 and 13. With up to 60-100 meteors per hour predicted, observers may catch plenty of bright meteors streaking along in the light of the Moon." As an added treat, the Moon will be sweeping past Venus and Jupiter in the eastern predawn sky.
While the meteors are certainly bright, they are typically not much larger than a grain of sand; however, as they travel at immense speeds, these tiny particles put on an impressive show. Due to the way the comet’s orbit is tilted, dust from the Swift-Tuttle falls on Earth’s northern hemisphere. Unfortunately, this leads to extremely low visibility for those in Australia, New Zealand and portions of South America.
Amateur Radio and the Perseids
If you own a 6 or 2 meter SSB/CW transceiver, you can get in on the action, bouncing your signals off Perseid meteor trails and making quick meteor scatter contacts over hundreds of miles, and possibly even as much as 1200 miles. Meteor scatter operation is particularly easy on 6 meters where 100 W and an omnidirectional antenna will do the job. On 2 meters, a directional antenna (such as a multielement Yagi) usually yields better results.
Some meteor scatter operators prefer to use SSB, making rapid exchanges of signal reports and grid squares. In recent years, digital meteor scatter has been increasing in popularity. With the free sound-card-based WSJT software suite by Joe Taylor, K1JT, it is possible to make digital meteor scatter contacts almost any time of the day or night, not just during annual showers. Most WSJT scatter operators use a mode known as FSK441 and center their activities on calling frequencies at 50.260 and 144.140 MHz. They also announce their availability by using Web sites just as N0UK's Ping Jockey Central.
Watching the Perseids
To get the most enjoyment while watching for Perseids, find a dark spot with an open sky view, bundle up thoroughly in blankets or a sleeping bag and lie back in a reclining chair. Spacedex.com recommends that once you have settled down at your observation spot, look approximately half way up the sky toward the northeast: "This way you can have the Perseids’ radiant within your field of view. Looking directly up at the sky or into the radiant is not recommended since this is just the point in which they appear to come from. You are more likely to see a trail when looking slightly away from this point." Just gaze into the stars and be patient. Any light pollution will cut down on the numbers, as will the radiant’s lower altitude earlier in the night. But the brightest few meteors shine right through light pollution, and the few that happen when the radiant is low are especially long, skimming the upper atmosphere and flying far across the sky.
Not all the meteors in the sky are Perseids. In addition to occasional random, sporadic meteors, the weaker Delta Aquarid shower is also active during Perseid season. The Delta Aquarids are slower, often yellower and track away from a radiant point in eastern Aquarius. Weaker still are the Kappa Cygnids, identifiable by their flight direction away from Cygnus in an altogether different part of the sky.
- ARRL
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