Perseids Meteor Shower: August’s Nighttime Fireballs

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Submitted by Malcolm Warren, Bayside Astronomy Program Manager

Every year, through the period of late July to late August, one of the cosmos most spectacular light shows dances its way across the night sky. The Perseids meteor shower is well known to the public as one of the most beautiful meteor showers to observe during the year, and for good reason. The name of the meteor shower, the Perseids, comes from the fact that the meteors appear to come from a point in the constellation of Perseus. This idea of an origin point is known as the meteor shower’s radiant, and is common in many meteor showers. Most meteor showers share this aspect of being named after the constellation the radiant appears to be in. To observe the shower, all you need is a chair, a reasonably dark sky, and patience, as most meteors can be seen whizzing by with the unaided eye.

On average, during its peak, the Perseids will display at least 60 meteors per hour, but can sometimes reach nearly two hundred per hour. The peak is usually around August 12th, and in 2019 the peak lands right on that day, peaking the night of August 12th and into the early morning hours of August 13th. The expected hourly rate in 2019 is between 60-80 meteors per hour, or around one every minute. However, this rate may be significantly hindered by the full Moon which occurs on August 15th, only a few days after the peak. Due to the Moon getting more illuminated each night before and during the peak, a near fully illuminated Moon will be up for much of the night on August 12th, and the brightness of the Moon could drown out many of the fainter meteors. This also means on days slightly off peak, where the number of meteors is still higher than average, the Moon could reduce the number seen. However, even with the Moon, occasional bright meteors should still be visible through the night of August 13th and early morning of the 14th.

On the day of the peak, although you don’t need to be watching during the peak, the best time to see the most meteors are during the pre-dawn hours of the morning. The reason for this also has to do with the reason the showers happen at the same time and appear to come from the same constellation each year. The Perseids, just like most meteor showers, are caused when the Earth passes through a small cloud of dust and debris from the tail of a comet. This cloud of dust also sits on the orbit of the comet, so when the Earth crosses this orbit the meteor shower will occur once more. In the case of the Perseids, the debris is from the tail of the comet Swift-Tuttle.

Swift-Tuttle the comet made its last near pass by Earth in 1992, which explains why in 1993 the Perseids were particularly intense, with an estimated 200-500 meteors per hour. The debris ranges in size, but generally speaking the meteors can be between the size of a small pebble and grain of sand. The reason particles so small can be so bright is due to the immense speed they travel through the air, with speeds ranging from 10-7 km/sec. Passing through the debris of a comet’s tail also explains why the best times to see the meteors are during the pre-dawn hours, as that is when the side of the Earth an observer is on is heading almost straight into the cloud of dust, due to the Earth’s movement around the Sun. 

Since the constellation of Perseus is best seen in the northern hemisphere, so too are the Perseids best seen in the northern hemisphere. As a result of the shower taking place in August this means that in Canada, the best times to see the showers are 4:30-5:30 am, when it is still dark enough to see the meteors before the Sun rises, but close enough to dawn that the Earth is facing its orbit head on, allowing for the greatest number of meteors to be seen.