Observe the Perseid Meteor Shower

Perseid meteor shower map
The Perseid meteor shower appears to stream from the direction of the constellation Perseus each year. It peaks around August 11. Carolyn Collins Petersen

The Perseid meteor shower is one of the best-known showers in the year. It's one of the great astronomy events of Northern Hemisphere summer and Southern Hemisphere winter. It begins in late July and extends halfway through August, peaking around August 11 or 12th. When conditions are good, you might be able to see dozens of meteors per hour. It all really depends on the weather and what part of the meteor stream Earth moves through each year.

Also, the viewing is best when there's no interference from the Moon, although you can still see the brighter meteors as they flash through the sky. 

What Causes the Perseids?

The Perseid meteor shower is really material left behind by Comet Swift-Tuttle. It passes through our part of the solar system every 133 years. As it travels, this icy dirtball leaves behind tiny grains of ice, dust, rock, and other debris, similar to a messy tourist scattering debris from an automobile. As Earth makes its trip around the Sun, it passes through this debris field with some spectacular results, which we know as the Perseids.

As Earth moves through the stream — which can stretch across 14 million to 120 million kilometers of interplanetary space —  its gravity interacts with the particles and spreads the stream out. As the comet passes by, it releases new bursts of particles, constantly refreshing the supply of material that will eventually collide with Earth's atmosphere.

The stream changes constantly, and this affects future Perseid meteor shower events. Sometimes Earth passes through rather thick areas of the stream, and that results in a heavy meteor shower. Other times, it traverses a thin part of the stream, and we don't see quite so many meteors. 

Although there are many meteor showers annually, such as the Leonids, Lyrids, and Geminids, to name a few, the Perseid shower is the most reliable, and can be very spectacular if conditions are right.

How it looks depends on several factors — ranging from whether the Moon is nearby (and bright enough to wash out the view) — to what part of the stream Earth encounters. The stream is not uniformly thick with particles, so some years the supply of materials might be less than others. In any given year, observers see anywhere from 50 to 150 meteors an hour on average, increasing at times to around 400 to 1,000 per hour. 

The Perseid meteor shower, like other meteor showers, is named after the constellation from which it appears to radiate: Perseus (named after a Greek mythological hero) which is located near Cassiopeia, the Queen. This is also called the "radiant", since that is the direction the meteors seem to travel from as they streak across the sky.

How Do I View the Perseid Meteor Shower?

Meteor showers are easier to view than many other astronomical objects or events. All you need is a fairly dark location and a blanket or lawn chair. Always make sure you have a jacket handy, even if you live in a warm weather climate. Viewing late at night and early in the morning can expose you to some chilly temperatures. It may be useful to have a star chart to help you locate Perseus, and other constellations while you’re watching, but it’s not a necessity.

The shower is active from mid-July each year when Earth enters the outer edges of the Swift-Tuttle stream. The best viewing time varies but is often between 2:00 and 4:00 a.m. around the 12th of August. The actual peak time ranges from the 9th to the 14th and then tapers off after that. For August 2017, the best viewing time is after midnight early in the morning of August 12th. There will be some interference from the Moon, which will be just past full. But, you should still be able to see the brightest ones. Also, start watching a few nights before and continue a few nights after; Perseids happen for nearly three weeks.

Find a good, safe viewing area where you can get a clear view of the sky. Arrive early to set up, and give yourself time to adjust your eyes to the darkness. Then, just sit (or lie) back, relax, and enjoy the show.

Most of the meteors will appear to radiate from the constellation Perseus, and streak across the sky. As you gaze, make note of the colors of the meteors as they streak through the sky. If you see bolides (larger streaks), note how long they take to traverse the sky and notice their colors, too. The Perseids can be a very rewarding observing experience for anybody — from younger children to experienced stargazers. 

Edited and expanded by Carolyn Collins Petersen.