Good news, and bad, about this week's meteor shower
Thursday, August 10, 2017, 11:37 - The peak of the Perseid meteor shower is brightening our night skies this weekend, but this year, there's some good news and there's some bad news.
What and when?
First off, the Perseid meteor shower, or simply 'the Perseids', is one of the best meteor showers of the year.
Not only does it deliver up to 100 meteors per hour, at least under ideal conditions, but it has the highest number of bright fireball meteors of any meteor shower of the year. A fireball meteor is one that flashes at least as bright as the planet Venus is in our night sky (or enough to be visible despite typical levels of light pollution).
The Perseids are caused when Earth passes through a stream of icy, rocky debris left behind by a comet known as 109P/Swift–Tuttle. The meteoroids in this stream - which range in size from specks of dust up to pebble-sized pieces - were left behind as the comet flew through the inner solar system, and its outer layers were blown off by the Sun.
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We see meteors flash in the night sky when the meteoroids from the debris stream hit the top of Earth's atmosphere, travelling at incredible speeds - over 200,000 km/h (124,274 mph). When they plunge into the atmosphere, they compress the air in their path, heating that air to the point where it glows. This heat quickly vapourizes the ice and smaller particles of dust and rock, so each meteor flash tends to be very brief. Larger pieces of debris compress more air, producing a bright flash and more heat, but they are more resilient, resulting in bright fireball meteors that can last significantly longer than a normal meteor. Some of these larger pieces may even survive their entry into the atmosphere, as they are slowed by their interaction with the air so that their meteor flash does dark, and they simply fall to Earth as tiny meteorites.
From start to finish, the Perseids run from around July 23 to August 20, each year, but the stream of debris has a more concentrated core, which produces a "peak" to the meteor shower, either on the night of August 11-12 or August 12-13. This year, in 2017, the peak is timed so that we should get a good view on both nights.
The good news
The good news about this year's Perseid meteor shower is that astronomers from NASA's Meteoroid Environment Office are forecasting that it will be better than usual!
As shown in the simulation below, the meteoroid stream from Comet Swift-Tuttle is not completely uniform, so there are times when we pass through more diffuse sections, and other times when we pass through parts where the comet debris is more concentrated. So, while the shower is fairly consistent, there is still some variation from year to year, and some years turn out to be exceptional.
Last year, astronomers said that the 2016 Perseids were going to be one of the best showings in years, due to Earth passing through a particularly dense part of Comet Swift-Tuttle's debris stream. Their forecast was right, and at the shower's peak, some skywatchers saw over 200 meteors per hour!
This year is not expected to be quite as good as it was last year, but we're still supposed to be passing through a somewhat denser part of the stream than usual. Those watching the meteor shower from under clear, dark skies could see up to 150 meteors per hour!
FAST PERSEID FACT: The 2017 Perseids may be better than usual, but don't believe anything you see on the internet about this year's meteor shower being the "brightest in human history". The source of this nonsense claim is unknown, but there's no truth to it. It may be that we've debunked that tired "Mars will be as big as the Moon" meme enough that the internet needed something new to go viral.
The bad news
While this year's Perseid meteor shower is expected to give a stronger showing than usual, there's one thing working against us - the Moon.
The night of the Full Moon was August 7-8, so on the nights of August 11-12 and August 12-13, it will still be roughly three-quarters full. Rising at around 11 p.m. on Friday night, and around midnight on Saturday night, the Moon will present a source of light pollution in the sky, that will washed out many of the fainter meteors.
Remember, any competing source of light - city lights, street lamps, car headlights, cellphone screens, the Moon, etc - will prevent our eyes from completely adjusting to the darkness, and thus prevent us from seeing all the meteors that will be flashing overhead.
The news may not be all bad, though. Along with an increase in fainter meteors, chances are we will see an increase in bright fireball meteors as well (or at least that's the hope!). So, while the Moon may prevent us from seeing all of the increased activity for this year, we may still see more fireballs, which are a spectacular part of the Perseids, every year.
Tips on viewing
The weather is going to play a large role in this event, of course, as clear or cloudy skies will determine who will actually get to see the meteor shower. See above for the current cloud forecast for Friday night through Sunday morning.
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If skies are clear in your area, you can find the meteor shower "radiant" - the point in the night sky where the meteors appear to originate from - by looking in the north or northeastern sky, throughout the night.
The Perseids radiant, to the northeast at midnight on August 12-13, 2017. Credit: Stellarium/Scott Sutherland
Even so, it's best not to focus just to the north, because the meteoroids from the debris stream can hit the atmosphere at any point in the sky overhead. Instead, bring along a blanket or a lawn chair, so you can sit or lie down, and look straight up in to the night sky. Taking in as much of the sky as possible will give a much better chance at seeing as many meteors as possible. Also, keep bright sources of light (the Moon included) out of your direct field of view.
The best place to see the Perseid meteor shower from is outside of your local city, town or village, away from sources of light pollution.
For most areas of the U.S., this likely involves a simple trip to the rural areas around your community, where there is no direct impact from urban lights.
Regardless of where you live, many national parks offer a great place to view these events, even if you have to stick to the parking lot at night.
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