Get out the lounge chairs, blankets and something to help stay awake because one of nature’s annual light shows will be on full display this weekend.
The Perseid meteor shower actually starts in July, but around Aug. 11-12 the frequency of meteors that can be spotted per hour will peak and, hopefully, put on a spectacular show.
The Perseid meteor shower is actually named for the constellation of Perseus – a hero from Greek mythology – because they appear from observers on Earth to emanate from that constellation, but are actually the result of Earth passing through the trail of debris left behind by Comet Swift-Tuttle.
“Swift-Tuttle is kind of like a Halley’s-style comet. It’s called a short-period comet,” said Greg Arkos, professor with Vancouver Island University’s department of physics, engineering and astronomy. “Halley’s comet comes back every 76 years … Swift-Tuttle is a little longer. It’s about twice as long as that, at 130-ish years, and it comes back regularly, as well. So it’s not one of those sun-grazing comets or ones that are on hyperbolic orbits. It’s actually a nicely well-behaved comet. It goes around and then it comes back every once in a while and dumps some more material and goes away.”
Swift-Tuttle’s orbit carries through our Solar System around the sun, but it travels a long way to get there, from as far out as about 7.7 billion kilometres from the sun in a region Neptune and Pluto call home, known as the Kuiper Belt where some comets are believed to have their origins.
According to NASA, Swift-Tuttle is a large comet with a nucleus of about 26 kilometres in diameter. Arkos describes comet composition as being like “dirty snowballs” made up of dust, ice, and frozen gases such as carbon dioxide, methane, ammonia and carbon monoxide. As comets approach the sun during their orbits the radiation heats them and causes them to expel debris and gases, which form the comets’ tails. When Earth’s orbit around the sun passes through the path of a comet’s orbit, the bits of dust in the debris field burn up from the friction from passing through Earth’s atmosphere at thousand of kilometres per hour.
“Generally speaking, they’re largely volatile,” Arkos said. “They’re like this ice and gas mixed with some solids thrown in. That’s why they melt when they start getting closer to the sun ... Luckily, they go by the sun so fast that they don’t spend too long and only a small percentage melts off in any given pass, but eventually they will melt all the way to nothing.”
Observers on Earth see the glowing streaks of dust and fireballs – which the Perseids are known for – created by small rocks when our planet passes through a debris field left behind by one of Swift-Tuttle’s previous orbits.
“Then we run into that at one particular point in the year, which is in August for us ... and just depending on how much stuff is happening to be moving through there, we get a really good show or a less good show … that debris keeps on orbiting around unless it happens to hit us in which case it burns up and it’s gone,” Arkos said.
During the peak of the Persied meteor shower, if there were perfect dark sky conditions, observers would be able to see about 100 meteors per hour, but this year’s peak shower time will be accompanied by the moon in its first quarter, which will brighten the night sky, making it more difficult to see the smaller, less bright meteors, until the moon sets after 11 p.m.
“So if you really want the best conditions you probably want to wait until the moon has set and the constellation of Perseus ... has risen. It’s in the northeast part of the sky and it’s quite low to begin with, and then it will rise,” Arkos said. “So what happens is, over the course of the evening, Perseus gets higher and higher and that’s what you want to see because that’s where the meteors seem to come from.”
The professor suggests finding location where as much sky is visible as possible, preferably looking toward the northeast, and having a comfy lawn chair that can be tilted back, a blanket, hot coffee or other confection to help stay awake, and bug spray or mosquito coils to keep mosquitoes at bay.
“Then just relax and let your eyes dark-adapt, which will take 15 to 20 minutes, so don’t be looking at your phone every two seconds, let your eyes open up and find a darkish corner and just enjoy,” he said.
