BBC Sky at Night - UK (2021-08)

August 2021 BBC Sky at Night Magazine 33

also because you tend to experience more meteors

as you’re all looking at the sky in different directions.

The Perseids themselves can occasionally put on

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meteors that can light up the sky with a bright

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Some of the brighter ones may leave what is known

as a ‘persistent train’, which is a line of superheated

air and meteor ‘smoke’ that appears to glow for a few

seconds, and in some cases longer, after the shooting

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However you intend to enjoy this month’s Perseids,

remember that you can also help study meteor

showers by carefully recording what you either see

or capture on camera. Such observations on their

own might not seem important, but combined with

other reports can build into something with genuine

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has taught us anything, it’s that often seemingly small

results can have profound implications – something

that can be fun to ponder on as you watch the

Perseids darting overhead on a balmy August night.

> See ‘The Sky Guide’ for more details about when

to observe the Perseids (on page 46) and for tips

about photographing a meteor train (on page 55)

The number of meteors seen is often less than theoretical figures

How many Perseids might you expect to see?

If you read some of the media

coverage of meteor showers

like the Perseids, you might

think that, at their peak, these

events see a near-constant

rain of bright shooting stars

blazing across the sky. Real

meteor showers – while

captivating and absolutely

worth observing – are rarely

like this. One number that’s

often mentioned is the

Zenithal Hourly Rate, or ZHR;

this is a theoretical number of

meteors that would be visible,

on average, over an hour with

the radiant of the shower at

the zenith and the viewing

occurring under perfect sky

conditions. The ZHR isn’t a

good indicator of how many

meteors you can expect to

see every hour, however; that

figure will be lower because of

things like light pollution and

the typically lower radiant

at the observing time. It’s

possible to roughly estimate

how many Perseids you might

spot, on average, near the

peak of the shower; such a

calculation suggests that

while observing at around

3am (BST) on the night of the

peak, a group of observers at

a suburban site – where the

naked-eye limiting magnitude

is, say, +5 – could potentially

see a rate of about 25

Perseids an hour or so.

A composite image can look

impressive, but observing meteor

showers, like the Perseids, is all

about managing your expectations

meteor

smoke

train

meteor

smoke

train

Will Gater is
an astronomy
journalist and
science presenter

A series of images

reveals a ‘persistent

train’ left behind

by a Perseid meteor