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Perseids

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Perseids
Photo: Sophie DesRosiers

They return year after year, and for many of us, they spell holidays and warm summer nights. But who — or what — are they? The Perseid meteors, of course!

Each year around mid-August, Earth passes close to the orbit of periodic comet 109P/Swift-Tuttle, whose wake is peppered with billions of dust particles that give rise to the famous Perseid meteor shower. However, the quality of the celestial show varies dramatically from year to year, mainly as a function of Earth’s distance from the densest parts of the particle stream, but also as a function of the Moon’s presence.

The Perseids in 2017

2017 won’t be a banner year for the Perseids. First, peak activity for the famous meteor shower will occur in the daytime for North American observers. The peak period will fall on August 12, most likely between 3 and 5:30 p.m., although possibly anytime between 10 a.m. and 10 p.m. according to past observations. The nights of August 11-12 and 12-13 will therefore both be equally far from this peak.

But it’s the waning gibbous Moon (the full Moon is on August 7) that will mask the shooting stars the most. It rises before 11 p.m. and will affect observation conditions in the second half of the night, in fact during the hours when the radiant reaches its optimal height and the Perseids put on their best show. Only the very brightest meteors (which are few in number) will be able to pierce that luminous veil. A short “dark period” will occur after the end of astronomical twilight and before moonrise, but the end of the night will be irremediably compromised by the presence of our natural satellite.

Put together, these adverse factors mean that we shouldn’t expect to observe more than a dozen meteors an hour on the two nights closest to the peak.

Since the Perseids are active from the end of July through the third week of August, it will be possible to observe a few shooting stars from that shower under dark, moonless skies — but one has to expect much lower numbers of meteors when observing farther from the period of peak activity. Prepare your wish list, just in case, and keep it handy!

Astronomical conditions will be much more favourable in 2018, so better luck next year!

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