7 December 2019 | New Scientist | 51The back pages
ALL^ CANADA^ PHOTOS/ALAMYSTOCK^ PHOTOStargazing at home online
Projects will be posted online each week at
newscientist.com/maker Email: [email protected]Abigail Beall is a science writer
in Leeds, UK. This series is
based on her book The Art of
Urban Astronomy @abbybeall
What you need
A dark winter night
at high latitude
For next week
Binoculars may be helpful
Next in the series
1 Mercury transits the sun
2 How to watch the Leonid
meteor shower
3 Venus and Jupiter
in conjunction
4 Mercury at its greatest
elongation
5 How to see the
Northern Lights
6 Find the Andromeda
galaxy
The most distant
object visible to the
naked eye
7 How to see Santa (the
ISS) on Christmas Eve
THE best chance to see Earth’s
aurorae is during the long winter
nights at high latitudes, which is
why they are also known as the
polar, northern or southern lights.
It is almost winter in the northern
hemisphere, although it is
summer in the southern
hemisphere, of course – but read
on to find the best places to spot
the aurorae when winter arrives.
The aurorae are generated
by the solar wind – a stream of
charged particles travelling from
the outer layer of the sun, or
corona, and slamming into Earth’s
magnetic field. This acts like a
shield around the planet that
deflects most of the particles.
But at its weakest points around
the poles, some can penetrate
into the upper atmosphere, where
they collide with and excite gas
molecules. As these molecules
de-excite, they release the photons
of light that make the aurorae.
The type of excited molecule,
along with the altitude of the
collisions, determine the colour
of the aurorae. The most common
colours are pale yellow and green
from oxygen molecules around
120 to 180 kilometres up. Less
frequent are red aurorae,
generated from oxygen around
200 km above the ground, while
red-purple aurorae come from
nitrogen below 100 km.
Most of us will have to travel
closer to the poles to catch a
glimpse of the aurorae, with
Iceland, northern Scandinavia,
Yukon in Canada and Alaska
popular locations in the northern
hemisphere. For the southernA dark winter night is best for seeing the northern and southern
lights, says Abigail Beall, as long as you head for a high latitudeStargazing at home 2 Week 5
See the spectacular aurorae
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Falkland Islands are good, along
with southern New Zealand,
and Tasmania and Victoria
in Australia.
The best aurorae happen when
solar activity is high. This is hard
to predict, although websites
and organisations that monitor
the sun can give a forecast for
the coming day, or even week.
The US National Oceanic and
Atmospheric Administration
website, for example, provides
observations for the past three
days along with 30-minute
predictions of the sun’s activity.
This is measured using the
planetary K index, or K-p, on ascale from 0 to 9. The greater the
K-p value, the higher the activity.
If it is a clear, dark night and the
sun looks like it will be active, get
yourself to a dark spot as far from
any light pollution as possible.
Then you need to wait and let
your eyes adjust. But don’t expect
aurorae in the stunning, bright
colours shown in photos. Seen
with the naked eye, the aurorae are
much subtler, and can be tricky to
spot the first time you try. If you
are in an area popular for aurora
watchers, consider going on a tour
with a guide who can show you
exactly what to look for and help
you capture those all-important
photographs. ❚