Page 82 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

OBSERVING

THE SUN

WHEN THE SHORT SUMMER NIGHTS AND LONG
SUNNY DAYS COME AROUND, THERE’S NO
NEED TO FRET ABOUT WHAT TO SEE – THE
DAYTIME HAS ITS OWN HIGHLIGHT

Stars are fascinating things: at However, the Sun’s close around the edges than it is in
the simplest level they make the proximity makes it brighter and the middle, an effect known as
patterns of the constellations. hotter than any other star in limb-darkening. You’ll also be
Some brighter examples the sky. Never look at the Sun able to see sunspots – providing
give hints of colour, like red using just your eyes, unfi ltered there are any around. Project
Betelgeuse in Orion. The trouble binoculars or telescopes – you the Sun over a few days and you
is, every night-time example risk permanent damage to your might see the sunspots move
is so incredibly far away. eyesight. There are a number of and change shape because the
Fortunately, the Sun is one star options to view the Sun safely. Sun rotates quite slowly.
that’s right on our doorstep and If you have a refracting
it’s available for everyone to look telescope, try the projection FILTERING OPTIONS
at, understand and, depending method. Line the telescope up If you want to move on from
on how you’re looking at it, gasp with the Sun (remembering projecting, you can buy fi lters
in amazement. not to look at the Sun through that fi t over the big, front lens of expensive glass white-light
The Sun, our source of the telescope) and then hold your telescope. These objective fi lters give a more natural
natural light and warmth, and up a piece of card close to the lens fi lters allow you to look orange-yellow look to the Sun’s
the star that made life possible eyepiece so that an image of the directly through the telescope at disc (see ‘Sights on the Sun’,
on our planet, is just next door Sun falls onto it. the Sun. Because it’s quite risky on page 84).
in astronomical terms. On When projecting the Sun, to point your scope at the Sun, Then there are the costly
average, it’s only 150 million you’ll be able to see that its these fi lters must fi t properly hydrogen-alpha (H-alpha) and
kilometres away. disc appears slightly darker and must not be damaged in calcium-K (CaK) fi lters and
any way. Before you go out to dedicated telescopes. These
observe the Sun, be sure to seek fi lter all the light and heat
expert advice from a reputable coming from the Sun except in
astronomy shop. wavelengths of hydrogen-alpha
PETE LAWRENCE X 2, THINKSTOCK, COLIN CUTHBERT/SCIENCE PHOTO LIBRARY
Solar fi lters block out what or calcium.
you don’t want to reach your At the H-alpha wavelengths,
eye: the Sun’s infrared heat, its you’ll get orange views of
ultraviolet radiation and 99.9 the features in part of the
per cent of its light. What you Sun’s atmosphere called the
get is a greatly dimmed, safe chromosphere, where dramatic
image of the Sun. You’ll be able solar fl ares and outbursts called
to see sunspots and those dark prominences take place.
solar edges through the scope Looking through a CaK fi lter
and, depending on what kind of allows you to see magnetic
fi lter you buy, the Sun will be storms that occur lower in the
displayed in a different colour. chromosphere, all in a fetching
The cheaper ‘white-light’ fi lters purple. So although these are
are made of mylar (aluminium two expensive options, they
A hydrogen-alpha fi lter will enable you to safely see amazing sights plastic sheet), which gives the certainly produce the ‘wow’
like solar fl ares bursting from the Sun’s surface Sun a blue tinge, while more factor when looking at the Sun.
82 skyatnightmagazine.com 2012