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 2016
Though not exceptional this year, the Perseids should none-the-less provide a very good performance for North American observers.
While maximum activity for the Perseids is expected between 9:00 and 11:30 a.m. (Eastern Time) on August 12, recent years’ observations suggest that maximum could occur anytime between 4 a.m. and 6 p.m. In eastern Canada, the latter hours of the night of August 11 to 12 will be closest to maximum.
The Moon will be at first quarter on the 10th, and will set shortly after midnight during the night of August 11 to 12: this will set the stage for excellent observing conditions during the second half of the night until dawn, just as the shower’s radiant, the area in Perseus from where the meteors appear to emanate, climbs higher in the sky.
Taking the time to travel away from light pollution, to the darkest observing site possible, will render the most from these ideal conditions. Under a moderately dark sky, about 25 meteors per hour should be visible — more than 50 per hour at a site completely devoid of light pollution.
The “normal” peak could also be preceded by an initial, short-lived increase in activity: Some specialists predict that Earth will venture near the dust stream liberated by comet Swift-Tuttle during its 1732 passage close to the sun. However, considering the predicted time of this initial peak (between 8 p.m. and midnight on August 11), observers in Europe are most favourably situated to view it.
Should the weather not cooperate during the August 11-12 timeframe, keep in mind that the Perseids are also visible a few nights before, and after, the period of peak activity — but one should expect to see significantly fewer meteors. In fact, you can spot Perseids as early as mid-July, until the third week of August, while the meteor shower remains active.
Let’s hope for clear skies… and get your wish lists ready!