BBC Sky at Night - UK (2021-08)

Emily Winterburn is is author of The

Quiet Revolution of Caroline Herschel:

The Lost Heroine of Astronomy

How to spot

NOCTILUCENT CLOUDS

Five top tips for spotting NLC displays

1. Look for NLCs in the
   northern sky, 90–120 minutes
   after sunset, between the end
   of May and start of August.
   They sometimes appear at
   the same time before sunrise.


2. Ensure you’re facing the
   right direction, by looking
   towards the bright star
   Capella (Alpha (_) Aurigae) in
   the constellation of Auriga.
   3. If you plan to take
   photographs, use a tripod
   and an exposure time of
   between 2 and 6 seconds.
   4. It’s hard to predict the
   weather but try and choose a
   day with clear skies.
   5. Look out for white or
   electric blue clouds, maybe
   with a herringbone or
   rippling sand-type pattern.

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coined the name we still use today: ‘noctilucent
cloud’. Studying his earlier observations, he concluded
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visible before this; he then organised a programme
of systematic photographs to be taken so further
investigations could be made of what and where
these clouds were.
NLCs are in fact ice crystals and dust found in
the mesosphere (in the upper atmosphere at an
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enough to make them visible during daylight hours.
Recent studies suggest the phenomenon may be
exacerbated by climate change and the increased
concentrations of atmospheric methane. Dust from
events such as volcano eruptions and Space Shuttle
launches can also make them more likely to occur,
showing that Backhouse’s initial thoughts weren’t
quite as wrong as his successors believed.
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instrument to detect NLCs from space. Today,

it is the AIM (Aeronomy of Ice in the Mesosphere)

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most in-depth studies of these clouds. This satellite is

dedicated to the study of NLCs and its work over the

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and where NLCs are most likely to be visible.

Other atmospheres

It would seem that NLCs are not unique to our planet.

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sky. More recent observations by the Curiosity rover

suggest some of these clouds might be made of

frozen carbon dioxide rather than water ice, which

may help scientists determine their altitude. Who

knows, perhaps the next breakthroughs in research

into NLCs will come not from our planet, but from

settlers on Mars?

August 2021 BBC Sky at Night Magazine 73

A 2010 view from the International

Space Station reveals NLCs in

Earth’s atmosphere

NASA’s Curiosity rover spotted these NLCs on

Mars over Mont Mercou, appearing high in the

atmosphere after sunset on 19 March 2021

For the best chance of seeing an NLC

display, locate the bright star Capella in

the constellation of Auriga, the Charioteer