Perseus and the Perseids

August is the absolute best month for observing the starry sky, thanks to the warm summer weather and fewer mosquitoes.

A major event that occurs every year during this balmy season is the famous meteor shower called the Perseids. From late July through about the third week of August, our spacechip Earth, in its trajectory around the Sun, passes through the stream of debris left by comet 109P/Swift-Tuttle over thousands of years.

Discovered iin 1862 by American astronomers Lewis Swift and Horace Parnell Tuttle, this comet has an orbital period of 133 years and was last near our Sun in 1992. Present generations will sadly never get to see it. With each visit, however, the comet sheds massive amounts of fragments (dust, rocks and other icy particles) no more than a few millimetres in diameter. These debris plunge into our atmosphere at a scorching speed of 60 km per second—more than 200,000 km per hour—where they heat up and illuminate the air around them, creating the streaks of light that we see. Every year, an estimated 100,000 tonnes of these dust specks, from all meteor showers combined, burn up in Earth’s atmosphere.

The Perseids will peak the night of August 12-13, more precisely between 10 p.m. on August 12 and 11 a.m. on August 13. For best viewing, find a dark location free from light pollution (ideally away from the city) and look to the northeast towards the constellation Perseus. While the showers will once again grace our skies this year, moonlight will unfortunately spoil the show. The Moon will be full on August 15 and the resulting glare will outshine the dimmer meteors.

How do you find Perseus? It’s easy, if you know a bit about mythology. Perseus, the son of Danae and Zeus, is the hero who killed the Gorgon Medusa, whose gaze literally turned people to stone. On his return from slaying the Gorgon, Perseus saved Andromeda (recognize the constellation name?), who had been sacrificed to a sea monster in atonement for the boastful words of her mother, Cassiopeia (another constellation). Long story short, Perseus ends up marrying Andromeda. If you can make out Cassiopeia in the sky, then you’ve found Perseus! As the sky darkens, look to the northeast for the prominent W-shaped constellation Cassiopeia, then look below the “W” and you’ll see the constellation Perseus. That’s the direction from which the Perseids will seem to originate, although the meteors can appear anywhere in the sky.

Mercury rewards early risers...

Mercury will be visible every morning between August 4 and 29, just before the Sun comes up. The planet reaches greatest elongation this month, appearing far enough from the Sun as to not be lost in its brightness. So, if you have a clear view of the horizon, you should be able to spot the tiny planet low in the east-northeast, 45 minutes before sunrise. The best visibility occurs from August 10 to 20.

…but the sky offers a good showing to early sleepers!

Use the Moon as your celestial guide: It will hang just above Jupiter on the evening of August 9, around 9 p.m., helping you to locate the giant planet. At the same time two days later, it’s Saturn’s turn to stand left of the Moon. Grab a small telescope and check out Jupiter’s cloud bands and Galilean moons and Saturn’s clearly visible rings while the two planets are still high enough to be seen in the early evening sky... the show will have you oohing and aahing!

Venus and Mars, on the other hand, are unobservable since they’ll be in the same direction as the Sun this month.

Clear skies!