The big three

BEST TIME TO SEE: 1–23 August, peak on the night of 12/13 August

August is the month when the Perseid meteor shower reaches peak activity. Fortunately, it’s one of the most prolific showers in the annual calendar and a fairly reliable performer. The enemy of meteor showers is moonlight and this year, although present, the Moon should be reasonably manageable.

The Perseid peak for 2020 is expected to occur between 14:00 BST (13:00 UT) and 17:00 BST (16:00 UT) on 12 August which is, of course, during daylight hours.

This means the best opportunities for spotting Perseid meteors will be on the nights of 11/12 August and 12/13 August.

On the night of 11/12 August the Moon will be just after its last quarter phase, 47%-lit. It rises at 23:50 BST (22:50 UT), reaching a height of 30˚ at the end of astronomical darkness. The following night, the now 37%-lit crescent Moon rises at 00:10 BST on 13 August (23:10 UT on 12 August) and reaches a height of

27˚ as darkness ends.

The best strategy for dealing with the Moon will be to simply block it out. Although it will cast some light across the sky, at half phase or less, this will be significantly reduced compared to a bright gibbous Moon. A building or fence that blocks its light should be sufficient to retain reasonable darkness.

Perseid rates typically climb and fall quite steeply in the hours running up to and from the peak itself. In addition, the orientation of Earth with respect to its motion around the Sun changes through the course of a 24-hour period. Your local position is best placed in the hours after local midnight, when your part of Earth has effectively turned to face incoming meteoroids head on. This raises impact energy, resulting in more and brighter trails. As the predicted peak period is fairly evenly positioned between the morning periods of 12 and 13 August, observing on 11/12 August should provide a decent build up to the peak. Although the evening of 12/13 August should still show the run down from the peak, Earth’s orientation pre-midnight UT will dampen this a little.

The shower is produced when Earth passes through dust debris strewn around the orbit of comet 109P/Swift-Tuttle. While a typical peak Perseid display produces a zenithal hourly rate (ZHR) of around 110 meteors per hour, bright events are common and brighter trails are often accompanied by a weakly glowing column of ionised gas known as a meteor train.

Perseid activity can typically occur between 17 July and 24 August, but outside the peak dates rates will be low. A number of weaker showers overlap the Perseids, providing quite a spectacle for August stargazers.