Out there somewhere in our solar system is a 26 kilometre wide comet, a chunk of dirty ice on a 130 year orbit of the Sun. This giant cosmic snowball was thought to have been born in the Oort Cloud, a vast spherical region of icy objects nearly 6 trillion miles from the Sun, almost a light year. With a total mass of roughly 40 times that of Earth, the Oort Cloud is so far out that the Sun’s gravity is weak but the gravity of nearby stars can have an effect, nudging these remote icy chunks out of position and sending them on a long journey towards the inner solar system. One of these mysterious icy travellers is called Comet Swift-Tuttle, much larger than the object thought to have spoiled the party for the dinosaurs, and the largest known chunk of space stuff to make repeated passes near the Earth. Although you can breath a sigh of relief, as it poses no degree of threat for at least a few thousand years, so we get to see its associated meteor shower without that bothersome mass extinction. Comet Swift-Tuttle, which last made its closest approach to Earth in 1992, is the particular comet in question that we’re interested in for August as it produces the Perseid meteor shower.
As this comet makes its way around the solar system it leaves a trail of dusty material in its wake. Every August as the Earth passes through this debris stream we get to see probably the most reliable and best meteor showers of the year. The fine grains zip through the atmosphere at 130,000 miles per hour, at a rate of up to 90 to 100 an hour. As with anything in astronomy it’s always best to view a meteor shower from a darker location, and hopefully with the bright Moon out of the way.
OK, so here’s where your view of the August 2011 Perseids may be taken down a slight notch as compared to other years. The Moon normally gives cracking views in your binoculars or telescope, but our old friend Lunar is nobody’s friend when it comes to meteor showers as its light can wash out all but the brighter of those spectacular shooting stars. This year we have a full Moon unfortunately on the two nights of the shower’s peak. This peak time is during the pre dawn hours of Friday the 12th and Saturday the 13th of August…so that’ll be the 11th beyond midnight, and the 12th beyond midnight. You have more chance of seeing meteors in the small hours as Earth faces into the shower during this time, resulting in the chance of seeing more and faster meteors. The Perseid meteor shower actually starts from the end of July and goes up until late August, but peaks on the mornings of the 12th and 13th of August. So keep your eyes peeled for Perseids in the weeks either side of the peak too. You’ll see the the Perseids seeming to radiate from, you’ve guessed it…the constellation Perseus. Although you can actually catch them streaking across any part of the sky, they’ll just seem to be coming from the direction of that constellation. Look to the north-east after dark and you’ll see Perseus rising, it then moves higher to the east before dawn. Even though the Moon will be in the sky during the peak, don’t let that dissuade you as it’s still well worth getting outside…don’t miss it.
The great thing about meteor showers is that the only equipment needed is your eyeballs, so everyone can join in. Get some friends and make a night of it, and the best thing about the Perseids is they conveniently come at the best time of the year when it’s nice and warm (hopefully). Meteor watching requires a lot of patience, but if you sit back, relax and put some time in you should be rewarded. There’s actually another night sky attraction to admire while you’re waiting for shooting stars, and that’s the solar system’s heavyweight Jupiter. The gas giant starts rising from the east shortly before midnight on the dates of the meteor shower peak. Check it out naked eye, but if you happen to have some binoculars with you grab a quick peek at the stormy planet blazing brightly at magnitude -2.36, and get a look at those moons. Don’t get too distracted though as you’ll want to keep an eye out for Comet Swift- Tuttle’s fireworks.
Don’t forget to get involved with Meteorwatch on Twitter…tweet your location and how many meteors you observe, and see your results on the Meteormap. Good luck !
Article by John Brady of Astronomy Central