The Perseids: Why is There a Meteor Shower?


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.

11 Replies to “The Perseids: Why is There a Meteor Shower?”

  1. I was wondering how come meteor showers pose no threats to the ISS or any satellites. I mean obviously particles are not going to rocket into it like fireballs, but the Earth is flying through space pretty fast. So if we cross paths with a chunk of comet (say the size of a baseball or golf-ball), couldn’t it potentially do some serious damage upon impacting orbiting spacecraft?

    1. It is a well-known risk to the ISS and other satellites, though in Low Earth Orbit you’re much more at risk of impacting something man-made than a natural micrometeoroid. There are hundreds of thousands of pieces of debris we’ve left up there over 50 years of space exploration, from bolts and washers to paint flecks. I’ve seen estimates of about a 1-in-100 chance of a debris event causing complete evacuation in any 6-month period. Over the lifetime of the station, it’s 1 in 5. It has already taken a few hits, too – the S1 radiator was damaged by a debris or micrometeoroid impact in 2008, though without major loss of function.

      The ISS is built to withstand the tiny sand grain-size debris, and given sufficient warning time can maneuver out of the way of something hazardous. Sometimes there isn’t enough warning time to take evasive action. The ISS was nearly evacuated in June due to a near-miss with a chunk of space debris that had pretty good odds of of hitting the station. The crew had only 15 hours warning, which wasn’t enough time to calculate a maneuver, so they had to suit up, get into the Soyuz escape capsules, and wait it out.

      It’s a risk, and one the astronauts are well aware of before they go to the ISS.

      1. Great explanation of the the risks involved MS.

        I was curious if any fireballs or meteors might be visible from the ISS (Cupola view, natch)? Meteors from the ISS have been observed before:

        (see also links and pics at bottom of that page)

        Maybe, despite the moonlight, a few brighter Perseids could be seen to burn up *below* the ISS. I hope someone up there might have some free time for a viewing session.

    2. Oh my word never thought of that! No doubt the guys and girls who go up there are made aware that they may come under attack from flying rocks? Great question interested to kinow the answer also!

  2. odds of being at the right spot at the right time are pretty small but not negligible. They have been hit up there before and not just the ISS.. but sooner or later it’s bound to happen,, Pray not.

      1. Thanks… yk
        Subject: [universetoday] Re: The Perseids: Why is There a Meteor Shower?

  3. If meteor showers are caused by the Earth moving into the path of dust and debris, does that mean they are only visible until midnight?

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