Page 54 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

FILTERS

THESE LITTLE ACCESSORIES CAN HELP YOU CUT
DOWN ON MOON GLARE AND EASE THE WOE
OF OBSERVING FROM LIGHT-POLLUTED AREAS

You can think of these small your viewing conditions, the
FOR THE MOON telescope accessories as object you’re looking at and
AND PLANETS sunglasses for your scope. what details you actually want
They work in a similar way, to see. There are different
too. Imagine a day with the fi lters for the different types
Sun shining in a clear blue sky. of objects up there: the Sun,
As you put on your shades the Moon, planets, stars,
the resulting scene becomes nebulae and galaxies.
dimmed as the lenses stop Some of you might have used
some of the light from getting fi lters in photography before,
COLOUR into your eyes. This ‘stopping’ and so may have some idea of
These are also known as is actually a fi ltering what to expect. However, it’s
planetary fi lters and are used out of some of the sunlight and worth taking a little time to
to bring out subtle details on this effect enables you to look understand what’s happening
the planets, such as Jupiter’s at things more clearly. to the light when it travels
clouds or the plains of Mars.
A basic set consists of blue, through each fi lter, and what
red, yellow and green fi lters. LESS IS MORE is the best use of a fi lter for a
Cost: Around £30 Filters for telescopes do exactly particular object.
the same thing: they take away, Some fi lters can appear to
or fi lter out, some aspect of be nothing more than innocent-
light heading down into your looking round bits of coloured Filters help cut out light
telescope, so you’re better glass from a church window. from bright objects
able to view starry objects. It’s However, there’s a difference. such as the Moon
quite strange to think that by
removing light you can
NEUTRAL DENSITY see better, especially when it Never look at
This is a good fi lter to begin comes to space views. We’re the Sun without SOLAR FILTERS
with, as it cuts down the light always told to make sure we get proper protection Viewing the Sun is completely
from the Moon. The fi lter different from looking at any
PETE LAWRENCE, GREEN-WITCH.COM X 3, TELESCOPE PLANET.CO.UK X 4, NASA, NASA/ESA
stops you being dazzled as much star light as possible to other astronomical object,
and enables you to see more the eye, but at times less really because of the dangerous
detail on the lunar surface. does mean more. And that’s strength of its light and heat. At
Cost: Around £12 the point of telescope fi lters:
no time do you want any of this
to remove unwanted light and intense light in your telescope,
thus bring out or emphasise the so solar fi lters are much larger
object – be it a nebula or a lunar than the others, fi tting over the
crater – that you want to see. entire main telescope aperture
and only allowing 0.01 per cent
The sheer variety of
of the light through.
telescope fi lters that are
Of all the fi lters, these need
ANTI-FRINGING available is incredible, and this the most care and attention.
If you have an achromatic can be quite bewildering for They should be stored
refractor, you may notice beginners. Some are coloured, safely and checked
blueish haloes around bright some block certain types of regularly to make sure
stars in the fi eld of view. This light, some are very cheap there are no scratches
fi lter sorts that out, while at just a few pounds, while or holes in them.
also helping to make planets They cost around £15
appear a little more crisp. others are expensive, costing for solar fi lm and
Cost: Around £45 hundreds of pounds. The fi lter around £75 for glass.
you should buy depends upon
54 skyatnightmagazine.com 2012