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 2022
The weather can’t be predicted months or weeks in advance, but from a strictly astronomical point of view, the Perseids will take place under very good circumstances in 2023. When the shower reaches its peak activity, sometime between 10 p.m. on August 12 and 5 p.m. on August 13 (Eastern Time), the Moon will be just a thin waning crescent and won’t spoil the view until the very last hour or two before dawn. The night closest to that expected “classic” maximum will be August 12 to 13, with the previous and next nights being very good alternatives if the weather doesn’t cooperate. Under clear, reasonably dark skies, away from light pollution, one could expect to count over 50 Perseids per hour on the morning of August 13.
Note that the window during which peak activity could occur is fairly wide—almost one full day. Indeed, observations from the last few years show there is some variability in the moment Earth comes closest to the dust stream from comet Swift-Tuttle. Secondary maxima have also been observed, sometimes up to one and a half days after Earth crosses the nominal centre of the meteor stream. This year, some numerical models forecast that Earth could cross a filament of comet dust released by comet Swift-Tuttle in 68 BCE, more than two millenia ago. That encounter is projected to occur between 9 and 10:45 p.m. on August 13, but the intensity and duration of the resulting spike of activity is impossible to predict—so keep your eyes open!
The Perseids are active from the end of July through the third week of August, though at much lower rates. Also, as the radiant of the shower climbs higher in the sky during the later hours of the night, the number of meteors steadily increases on a given night, until daybreak puts an end to your observing session. Don’t forget your wish list!
The outlook for 2024 is a mixed bag: around maximum, the first quarter Moon will interfere with the meteors during the evening hours; however, after the Moon sets (around 11:00 p.m.), the Perseids will benefit from dark skies until dawn.