For those who enjoy observing the night sky, summer is a great time of year to look for meteors blazing through the atmosphere, also known as shooting stars. Because of the favorable weather, more of us get the chance to go outside at night to look up. The Perseid meteor shower takes place each year from mid-July through late August, peaking in mid-August. With up to 100 observable meteors per hour, this particular meteor shower is easily among the most spectacular of the year. Additionally, the peak of this year’s shower coincides with a new moon, when the sky is much darker, so the 2018 Perseids will be especially exciting for stargazers.
What is a meteor shower, and where do the meteors come from?
As we discussed on the ISC blog in January, meteors originate from rocky objects in space that heat up as they enter Earth’s atmosphere. On any normal night throughout the year, one can expect to see only a handful of these shooting stars each hour. Every summer, however, our planet passes through a dense trail of debris left behind by the comet 109P/Swift-Tuttle during its visit to the inner solar system; as the giant ball of ice and dust heats up when it approaches the Sun, it sheds a tail of gas and dust particles into space behind it. Because the comet orbits the Sun along its own path, this debris distributes itself evenly around the whole orbit like a ring of dust. When the Earth passes through it, the stream of rocks left behind can send a meteor or two into our atmosphere every minute.
When these bits of space junk, (which are typically no larger in size than a pea) cross paths with Earth’s orbit, they can shoot across the night sky at speeds of nearly 40 miles per second – that’s almost 200 times the speed of sound! As they penetrate the upper atmosphere at high speed, the grains spontaneously heat up the air around them through friction, and the resulting flash of light is visible from the ground as shooting stars.
While the meteors seen throughout the year come from any random direction, those during a meteor shower all radiate from one point in the sky called the radiant. This happens because the grains shed by the comet all travel in a stream around the Sun. Like most other meteor showers, the Perseids get their name from their radiant, which can be found in the the constellation Perseus (more on that in a bit!).
Where and when to view the Perseids
To see as many meteors as possible, it is best to view the shower when it’s really dark outside, away from city light pollution. Besides light, weather is also a factor; in addition to blocking the sky, clouds and humidity can scatter and reflect light from the ground and make it even more difficult to see meteors, especially in urban areas. This year, the Perseids peak the evening after the new moon on August 11, making this the best time to see the shower. Prior to this date, viewing is best ahead of the moonrise before dawn. After the new moon, viewing is best once the moon sets after dusk.
Since the full moon was only a few days ago on the 27th, it is currently hard to see the meteor shower under complete darkness. Until the moon’s third quarter on August 4, viewing will be best during the first half of the night, with dark conditions that extend later with each night. This year’s Perseids will come to a close with another full moon on August 26, and during the final week of the shower, meteors are best viewed in the early morning hours.
To see the meteors, look toward the radiant as a guide, which is in the constellation Perseus. Not an expert stargazer? Don’t worry, a handful of stargazing apps are available for mobile phones that make it easier to find constellations. Most shooting stars will appear to travel outward from Perseus, but you might see the occasional streak left by a non-Perseid meteor from time to time going in any direction.
To see as many shooting stars as possible, avoid looking at bright lights beforehand – doing so can cause the pupils in your eyes to contract, making it harder for you to see at night. Under dark enough conditions, one can observe a flash or two every minute. But even for those who do not have time to escape the city, the brightest meteors should still be visible. Every so often, the brightest of the bright will leave a long, impressive streak that lights up the sky, so be sure to set aside at least a couple hours to make the most of this exciting astronomical phenomenon!