Sky-watchers are set to make a lot of wishes this week as the heavens open up with a flurry of shooting stars. The Perseid meteor shower is considered the "Old Faithful" of cosmic sky shows, peaking like clockwork every year on August 12 and 13.
The Perseids grace our skies when Earth plows into a stream of fragments—ranging in size from sand grains to boulders—left behind by a comet. These particles slam into the atmosphere at speeds of 100,000 miles (160,000 kilometers) per hour, causing the meteors to burn up in the upper atmosphere. The momentary streak created across the overhead skies is also known as a "shooting star."
At the same time each year, Earth passes through the dust trail of comet Swift-Tuttle, which swings around the sun every 130 years. This passage produces dozens of visible meteors per hour, some the size of a baseball or larger that can cause exceptionally bright meteors known as bolides or fireballs. During a meteor shower, your chance of glimpsing one of these impressive fireballs ripping through the upper atmosphere increases tremendously because of the higher density of space stones.
This year's fireworks promise to be particularly great for space buffs since the moon will in its new phase this week, which means its glare will not interfere with meteor-watching.
When is the best time to look up?
Current theoretical models of the cometary debris field indicate that the Perseids will peak between 9:30 p.m. EDT Wednesday and 10 a.m. EDT Thursday (for international skywatchers, that's Thursday between 1:30 GMT and 2 p.m. GMT). Observers in North America will be best positioned to observe the most meteors in the overnight hours.
The Perseids are primarily a Northern Hemisphere sky show because of comet Swift-Tuttle's orbit, but skywatchers in the southern hemisphere will still have the chance to observe the shower. It just won't be as brilliant.
Where in the sky will the shooting stars appear? The meteors will appear to radiate out from the shower's namesake constellation Perseus, which rises after local midnight in the northeastern sky. But you can face the northeast starting from local nightfall to catch even the straggler Perseids.
To catch the highest rates of meteors, though, it's best to look up when Perseus rises to its highest point in the sky, in the pre-dawn hours on Wednesday through Friday.
How many shooting stars will be visible?
Typically if sky conditions are dark, you can expect to see between 60 and 100 meteors per hour. The time of night and your proximity to dark skies make a substantial difference in what you can see. In suburban skies, expect rates anywhere from half to a third that many shooting stars per hour.
The International Meteor Organization, the astronomical clearinghouse for observer’s reports, suggests that every night after the peak date will see the number of shooting stars drop by half until about August 25, when the Perseids officially end.
How best to enjoy the meteor show?
The best place to see the Perseids is from a dark site away from city lights, with a clear unobstructed view of the overhead sky. No need for the high-powered views of telescopes or binoculars—unaided eyes are best since they can soak in the entire sky. Meteors can appear in all parts of the sky.
A great test for whether you have a dark enough sky to see all of the meteors in the offing is to see if the Milky Way is visible. However, even if you are stuck in the suburbs, there should be enough shooting stars to make plenty of wishes.
The only equipment needed is a blanket or reclining lawn chair and some hot chocolate.
For more sky events check out our weekly skywatching column.