One of the best shows in the night sky is here! The peak of the Perseid meteor shower began Wednesday night, and we can still catch this amazing event for the rest of the week.
Right now, as Earth travels along its orbit around the Sun, the planet is passing through a stream of debris left behind by a comet known as 109P/Swift-Tuttle. This comet only passes through the inner solar system once every 133 years or so. However, each year we are treated to a reminder that it's out there, as Earth sweeps up the bits of icy debris it leaves behind on each pass. When these tiny bits of ice and rock plunge into the atmosphere, they produce the streaks of light we call the Perseid meteor shower.
In this 30-second exposure taken with a circular fish-eye lens, a meteor streaks across the sky during the annual Perseid meteor shower on Friday, Aug. 12, 2016, in Spruce Knob, West Virginia. Photo Credit: (NASA/Bill Ingalls)
"If you happen to find yourself outside of the city or perhaps on a beach on Wednesday or Thursday night, look up! Every couple of minutes or so you will see a bright meteor zipping across the sky," Denis Vida, project lead of the Global Meteor Network, said in a Western University press release.
According to the International Meteor Organization (IMO), under ideal clear, dark skies, anywhere from 50-75 meteors per hour occur during the Perseids peak, which occurs around the 12th of August every year. Sometimes, this shower can deliver as many as 100 meteors per hour or more (again, under ideal conditions).
The Perseids radiant — where the meteors appear to originate from — is located in the northern sky, near the constellation Perseus. As such, it never sets below the horizon at this time of year. So, rather than having to wait for the radiant to rise during the night, skywatchers will start to see Perseids as soon as the Sun has completely set.
The location of the Perseids radiant at around midnight on August 11-12. Credit: Stellarium/Scott Sutherland
"The best show will be just before sunrise on either August 12th or August 13th," Vida said. "But if you are planning to observe in the evening hours on August 11th or 12th, start after 10pm and look either east or north-west. If you can locate the Big Dipper in the sky, look in its direction and you are bound to see some Perseids."
In their detailed 2021 meteor shower calendar (pdf), the IMO also mentioned the possibility of Earth crossing through a "filament" — a concentrated swath of meteoroids embedded within the comet's normal debris stream. If we did encounter this filament, it likely provided an added boost to the number of meteors seen in the predawn sky on Thursday.
Whatever night you get out to watch, the best time to see the Perseids during the night is usually in the hours between midnight and dawn. That is when the sky tends to be the darkest. Also, the meteor shower radiant is high in the sky at that time, which means that we are looking more or less straight into the path of the meteoroid stream.
This graph shows the average Perseid meteor activity from 2014-2020. Credits: Graph and background image courtesy NASA
This year, as long as the skies are clear, viewing will be better than we've seen for the past few years. This is due to the Moon.
With the shower peaking only a few days after the New Moon, there will only be a thin crescent Moon in the sky that night, which will set just a few hours after nightfall. This will leave behind a nice dark night sky, which will make it easier for us to see the show!
Read on for tips on how to get the most out of watching a meteor shower.
WILL WE SEE IT?
The timing may be perfect to put Earth in the middle of Comet Swift-Tuttle's debris stream, but will the skies cooperate to let us see the spectacular results?
Here is the current cloud forecast for Thursday night into Friday morning, across Canada and the northern United States.
Based on this, northern New Brunswick, eastern Ontario, the Prairies and British Columbia will have the best view. Clouds may spoil the show in southern regions of Ontario and Quebec, but check your local forecast to see if there will be patches through which to watch the meteor shower. Also, we have satellite cloud cover maps to double-check before you head outdoors.
If you wait until Friday night or early Saturday morning to watch, there should still be a decent number of meteors zipping through the sky. Here are the expected cloud conditions across the country for that night.
HOW MANY METEORS WILL WE SEE?
There is a complete guide on how to get the most out of watching a meteor shower farther down in this article. However, this question — "How many meteors will we see?" — deserves an early answer.
The number of meteors expected for any particular shower, as seen in astronomy guides, is known as the Zenith Hourly Rate (ZHR). Basically, it is the maximum number of meteors that could be seen under absolutely ideal conditions — perfectly dark sky, zero cloud cover, the meteor shower radiant directly overhead (at the 'zenith'), and if the viewer could spot every meteor that flashed by overhead, no matter how fast or faint it was.
This Perseid meteor was captured on August 11, 2019, from Lockeport, Nova Scotia. Credit: Barry Burgess/UGC
Unfortunately, these conditions are nearly impossible to satisfy in reality. So, assuming they are under reasonably clear skies and as far as they can get from city light pollution, the best-case estimate for any particular viewer is that they will see roughly half the ZHR value.
In the case of the Perseids, according to Bill Cooke of NASA's Meteoroid Environments Office, that's around 40 meteors per hour.
"That's about one every couple of minutes — not bad," says Cooke.
If you can't get away from the city for the event, the glare of urban lights will 'wash out' any dimmer meteors. Cooke says that if you're in the suburbs and can clearly pick out constellations like the Big Dipper, expect to see a meteor every 6-7 minutes. If you're right in the city core, you may only see 1 or 2 every hour.
Follow Cooke's advice: "Want to see Perseids? Then head out into the dark — it's worth it!"
Read on for more details on how to watch.
WATCH FROM ANYWHERE
If your skies are cloudy or you miss out on the opportunity to get outside for this event, don't worry! You can see the meteor shower from various online sources!
There's two fairly unusual and fascinating ways to witness a meteor shower, day or night, using Meteor Radar! Meteor Scan hosts a live, auto-updating view of colourful radar 'pings' that depict when meteors strike the top of the atmosphere. Live Meteors on YouTube streams nightly, allowing us to see and hear these same kind of radar echoes.
Also, each morning, the public can view fireball images and animations recorded by NASA's All Sky Fireball Network from the night before. Use the links along the left side of the page, to view the collection of fireball movies recorded each night (going back three weeks!), or watch the liveviews each night to see the action as it happens.
The SpaceWeather website also has a collection of Perseid fireball images, submitted by astrophotographers around the world.
WHAT'S GOING ON HERE?
Meteor showers happen when Earth encounters a stream of ice, dust, and rock left behind from a comet (or sometimes a special kind of asteroid). As Earth sweeps through the stream, the bits of debris plunge into the planet's atmosphere, travelling anywhere from 54,000 to 255,000 kilometres per hour. At that speed, these meteoroids compress the air molecules in their path, squeezing them together until they glow white-hot.
The bigger the piece of debris, the brighter and longer-lasting the meteor will be.
Watch below: Dozens of Perseid fireballs captured by NASA in 2020
The Perseids occur every year between July 17 and August 26, as Earth passes through the stream of debris from Comet Swift-Tuttle. 109P/Swift-Tuttle was last seen in the inner solar system in 1992. Right now, it's far out in the solar system, near the orbit of Neptune, and still headed even farther out. It will return in late 2125.
The Perseids are one of the strongest meteor showers of the entire year, and this alone makes it worth watching. However, there are two other ways this meteor shower distinguishes itself.
First, it has the most fireball meteors of any annual shower.
In the Royal Astronomical Society of Canada's Observer's Handbook 2021, Philip McClausland writes "Fireballs are exceptionally bright meteors that are spectacular enough to light up a wide area and attract public attention."
Watch below: An all-sky camera captures a brilliant Perseid fireball
The second is the ability of some Perseid meteors to leave behind a phenomenon known as a persistent train.
Meteors typically flash for a second and are gone. Fireballs can last up to around 10 seconds. Every once in a while, though, a very fast meteor will leave behind a glowing trail that is visible for a short time after the meteor flash has gone out. These are persistent trains. They can last for a few seconds, or a few minutes, and some have been reported to last for more than an hour.
Spotting persistent trains is apparently fairly common, depending on the meteor shower. Capturing them on camera, though, has been far less common.
Still, scientists have narrowed their cause to three likely reasons:
The first is the same reason for the initial meteor flash. Atoms in the meteoroid's path are compressed and heated until they glow. Basically, each of these atoms consists of a nucleus surrounded by a number of electrons. When the atoms are heated by their interaction with the meteoroid, one or more of those electrons absorb energy, and they emit a flash of light to dump that excess energy. For extremely bright fireballs, this can continue after the passage of the meteoroid, producing an 'afterglow' that lasts for a few seconds.
The second is due to some of the electrons receiving so much energy that they break free to zip around on their own, leaving behind a positively-charged atom (an 'ion'). When these ions 'recombine' with an electron, a flash of light is produced. This process can persist for a short time after the meteor flash.
"It only takes a brief moment before the atoms capture an electron and emit light, which is when you can see a glowing trail in the sky," said Vida.
The most persistent of persistent trains, though, appear to be due a third process known as 'chemiluminescence'.
Chemiluminescence is the production of light through a chemical reaction. When metals like iron and nickel vaporize off the surface of a meteoroid, they can chemically react with ozone and oxygen to produce a glow. Since these processes take much longer than the original meteor flash, the train can persist for up to an hour or longer.
Watch below to see a persistent train produced by a December Geminids meteor
Studying persistent trains hasn't been easy.
According to Vida, reproducing them in a controlled environment in the laboratory is "almost impossible." The vacuum chamber we'd need to lower the air pressure enough to match 100 km above the ground, and allow us to fire a tiny projectile at speeds of around 250,000 km/h, would need to be kilometres long. The largest chamber in the world — the Space Power Facility at NASA's Glenn Research Center — is tiny by comparison, only 30 metres wide and 40 metres tall.
Simulating persistent trains in the computer doesn't work out so well, either. In this case, the limitation is just how little we know about exactly what meteoroids are made of, and what their physical structure is like.
More observations, and capturing more persistent trains on camera, is needed to better undestand them.
METEOR? METEOROID? METEORITE?
The bright streaks seen from these showers are called meteors.
They are caused by meteoroids which are pieces of dust, rock, or ice floating through space. They can be leftover remnants of the formation of the solar system, or they can be left behind by the passage of comets or asteroids.
The smallest — ranging in size from microns to millimetres — tend to be called micrometeoroids. Anything larger than a metre in diameter is usually called an asteroid.
A primer on meteoroids, meteors and meteorites. Credits: Scott Sutherland/NASA JPL (Asteroids Ida & Dactyl)/NASA Earth Observatory (Blue Marble)
The larger an object is, and the faster it is going as it enters Earth's atmosphere, the brighter the resulting meteor will be. We call the brightest of these fireballs. A fireball that ends with an extremely bright explosion is known as a bolide. Some, like the asteroid that exploded over Chelyabinsk, Russia, on February 15, 2013, have been called superbolides.
Some fireballs and bolides end with bits of the meteoroid actually reaching the ground intact. When these are found, we call them meteorites.
TIPS FOR WATCHING A METEOR SHOWER
Here is an essential guide on how to get the most out of meteor shower events.
First off, there's no need to have a telescope or binoculars to watch a meteor shower. Those are great if you want to check out other objects in the sky at the same time — such as Jupiter and Saturn, which are up all night these days. When watching a meteor shower, though, telescopes and binoculars actually make it harder to see the event because they restrict your field of view.
Here's the three things needed for watching meteor showers:
Dark skies, and
Even a few hours of cloudy skies can ruin an attempt to see a meteor shower. Since the weather is continually changing, be sure to check for updates on The Weather Network on TV, on our website, or from our app.
Living in cities makes it very difficult to see meteor showers. Those living in suburban areas, with dark back yards shielded from street lights by trees and surrounding houses, may see the brightest meteors. Rural areas offer the best viewing, though, as they are far away from city light pollution.
For most Canadians, simply driving out into the surrounding rural areas is usually good enough to get under dark skies. However, if you live anywhere from Windsor to Quebec City, that will be more difficult. Unfortunately, getting far enough outside of one city to escape its light pollution tends to put you under the light pollution dome of the next city over.
Watch below: What light pollution is doing to city views of the Milky Way
In these areas, there are a few dark sky preserves. A skywatcher's best bet for dark skies is usually to drive north and seek out the various Ontario provincial parks or Quebec provincial parks. Even if you're confined to the parking lot, after hours, these are usually excellent locations to watch (and you don't run the risk of trespassing on someone's property).
Once you have verified you have clear skies, and you have limited your exposure to light pollution, this is where having patience comes in.
For best viewing, give your eyes time to adapt to the dark. Typically, this takes about 30 minutes of avoiding any sources of bright light (includes cellphone screens). Just looking up into the sky during this time works fine, and you may even catch some of the brighter meteors in the process.
Lastly, the graphics presented for meteor showers often give a 'radiant' point on the field of stars, showing from where the meteors appear to originate. Meteors can flash through the sky anywhere above your head, though. So, don't focus on any particular point in the sky. Instead, just look straight up and take in as much of the sky as you can, all at once. Also, since our peripheral vision tends to be better at night, you may be surprised at how many meteors you can catch from the corner of your eye!
Thumbnail image credit: Graham Fielding Photography/Submitted to The Weather Network
Author's note: after a discussion via email with Denis Vida, a post-doctoral researcher in Western University's Meteor Physics Group, the section on Persistent Trains has been updated to clear up a few misconceptions and to add more details on the limitations researchers face when studying the phenomenon.