The Perseids: Why is There a Meteor Shower?

Bright Fireball Credit: Adrian West


Every year from late July to mid-August, the Earth encounters a trail of debris left behind from the tail of a comet named Swift-Tuttle. This isn’t the only trail of debris the Earth encounters throughout the year, but it might be one of the most notorious as it is responsible for the annual Perseid meteor shower, one of the best and well-known yearly meteor showers.

Comet Swift-Tuttle is a very long way away from us right now, but when it last visited this part of the Solar system, it left behind a stream of debris made up of particles of dust and rock from the comet’s tail.

Earth encounters this debris field for a few weeks, reaching the densest part on the 11th to 13th August.

The tiny specs of dust and rock collide with the Earth’s atmosphere, entering at speeds ranging from 11 km/sec (25,000 mph), to 72 km/sec (160,000 mph). They are instantly vaporised, emitting bright streaks of light. These tiny particles are referred to as meteors or for the more romantic, shooting stars.

Perseid meteor shower
Perseid meteor shower

The reason the meteor shower is called the Perseid, is because the point of the sky or radiant where the meteors appear to originate from is in the constellation of Perseus, hence Perseid.

When the Perseid meteor shower reaches its peak, up to 100 meteors an hour can be seen under ideal dark sky conditions, but in 2011 this will be greatly reduced due to a full Moon at this time. Many of the fainter meteors (shooting stars) will be lost to the glare of the Moon, but do not despair as some Perseids are bright fireballs made from larger pieces of debris, that can be golf ball size or larger.

These amazingly bright meteors can last for a few seconds and can be the brightest thing in the sky. They are very dramatic and beautiful, and seeing one can be the highlight of your Perseid observing experience.

So while expectations may be low for the Perseids this year, keep an eye out for the bright ones and the fireballs. You will not be disappointed, even if you only see one!

Join in on twitter with a worldwide event with Universe Today and just follow along using the hashtag #meteorwatch ask questions, post images, enjoy and share your Perseid Meteor Shower experience.

Tonight the Planets and Perseids Put on a Show For Free

Celestial Navigation
Looking northeast around midnight on August 12th-13th. The red dot is the Perseid radiant. Although Perseid meteors can appear in any part of the sky, all of their tails will point back to the radiant. Credit: NASA

Just a reminder: It’s time to head up on the roof, to the backyard, the pasture, the mountaintop — wherever you have to go to get away from city lights and watch the Perseid meteor shower. But this year, there’s the added show of a planetary conjuction right at sunset. Venus, Saturn, Mars, tiny Mercury and the crescent Moon pop out of the western twilight in tight conjunction. But then stay tuned to the sky for the Perseids. If you haven’t been out to see them yet, Thursday, August 12 and Friday August 13 should be the peak, and already some locations have been reporting 70-80 meteors an hour. No telescope is required to enjoy these two naked-eye events. See below for a sky map and tips on how to share your experience.


Want to share the event via Twitter? Follow the hashtag #Meteorwatch and see the Meteorwatch website for all you need to know about watching the Perseids.

Meteorwatch even has a map of incoming meteors being reported on Twitter. Very cool!

There will also be live coverage on AstronomyFM

If you would like to contribute to science, the British Astronomical Society has a report form where you can submit how many meteors you are seeing.

The International Meteor Organization also has an online report form.

And Oana Sandu from the BAA has a list of tips for watching the meteor shower.

On Thursday, Aug. 12, from 3-4 p.m. EDT, astronomer Bill Cooke from NASA’s Marshall Space Flight Center will answer questions in a live chat about the Perseids and the best ways to view it. To view and join the chat, go to this link on Aug. 12 a few minutes before 3 p.m. EDT. A chat window will be active at the bottom of the page. Log in, then Bill will start answering your questions at 3:00 EDT. And then…stay up all night with NASA! Later that night — Aug. 12 — from 11:00 p.m. to 5 a.m. EDT, Bill will take your questions via Web chat. You can also “listen” to the Perseids on that page.

And for more detailed info about this year’s Perseid Meteorshower, check out our own article by astronomer Tammy Plotner!