The big three

BEST TIME TO SEE: 8–16 August, peak night 12/13 August

Everything’s falling into place for a potentially spectacular display of Perseid meteors this month. Generally, low-rate activity occurs between 17 July and 24 August with the exception of the peak period 8-16 August, a sharp peak typically seen around 11–13 August. The peak timing varies year on year. In 2021 it’s predicted for 20:00-23:00 BST (19:0022:00 UT) on 12 August. Rates naturally increase after local (non-daylight saving time) midnight, so the period from 01:00-03:30 BST on the 13th is optimal.

The Perseid shower is a solid performer, reaching a peak zenithal hourly rate (ZHR) of 100-plus meteors per hour. This is what you’d see under perfect viewing conditions with the meteor radiant overhead and the ability to see the whole sky. However, the actual visual hourly rate is often lower.

Two variable factors affect shower visibility; the weather and the Moon. There’s little you can do about the weather except move location if things look really bad. The Moon either interferes or it doesn’t. On 12 August, the 4.5-day old, 20%-lit waxing crescent Moon sets at 22:35 BST (21:35 UT) and won’t interfere.

Meteor showers occur when Earth passes through dust distributed around a comet’s orbit. Entering our atmosphere on parallel paths, perspective causes meteor trails to appear to emanate from the same sky location – the shower radiant. Over the activity period, the radiant’s position drifts against the background stars. Peak activity represents us passing through the densest part of the stream.

A garden lounger is a great viewing platform. Look for meteors at an altitude around 60˚ in any direction. While longest trails are seen 40–140˚ from the radiant, towards the radiant expect short trails. A

look in the opposite direction to the radiant will reveal trails that appear short and converge to a point called the anti-radiant.

Perseid displays often exhibit bright events, many of which show what appears to be an after image of the trail, which is a weakly glowing column of ionised gas. This ‘meteor train’ fades from view as the energy in the ionised atoms is given up. High altitude winds may also affect the train, distorting its shape.

See the ‘Perseid Perfection’ feature on page 28 for more on this year’s shower

View the best of the Perseids on the night of the 12/13 August between 23:15–03:20 BST (22:15–02:20 UT)

Make sure your eyes are properly dark adapted from around 22:30 UT (21:30 BST) on 12 August