Page 36 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

PROS & CONS SIMPLE

REFRACTORS
Pros
• They are robust – a
knock won’t do any harm.
• They need very little TELESCOPES
maintenance apart from
a dust once in a while.
Cons
• Many cheap models ALL ABOUT REFLECTORS AND REFRACTORS
are poorly made in terms
of their lenses, eyepieces
and mountings.
• Lenses suffer from Here’s a question for you: what is the only essential doing a little bit of homework fi rst, it’s unlikely
‘chromatic aberration’, thing you need if you want to call yourself an you’ll end up with the best scope for you.
where stars have a faint astronomer? Is it a good knowledge of fi nding So what do you do if you want a telescope?
halo of colour around your way around the night sky? No. Is it a broad One of the best ideas is to visit, if not join, your
them. Some more costly knowledge of the objects you can fi nd in space, local astronomical society. Many members will
refractors correct this by like black holes and nebulae? No. The answer is a be very keen amateurs who’ll not only show you
using a secondary lens.
• Larger refractors (100mm telescope! Just a simple telescope. a variety of scopes during one of their observing
and up) are quite heavy. It seems that is the perception of the subject, but evenings, but if you do buy one, will be able to help
of course that’s not true. I have known many people you work out how the thing actually works.
REFLECTORS who have decided astronomy is for them, and Another place you can go to see a range of
Pros before doing anything that I’m about to describe scopes is a recognised telescope dealer. Nearly all
• Size for size, these are below, out they go to buy a telescope that’s entirely of these suppliers have staff who know what they’re
cheaper than refractors.
Dobsonians – large inappropriate. Predictably, it just sits around not talking about and will be able to offer advice.
refl ectors on simple doing much before it’s sold on eBay. It’s worth pointing out that the reverse is also
mounts – are particularly true: if the shop selling telescopes also sells kettles
good value for money. THE RIGHT SCOPE FOR YOU and soft furnishings, then it’s very likely the sales
• Larger refl ectors are still ‘Inappropriate’ in this case means a scope that is team are not themselves dedicated to astronomy,
relatively light in weight.
the wrong size, shape or weight to make it useful to and they probably won’t be able to answer any
Cons the owner. You may want a light, small scope that’s questions you might have.
• Big knocks will send the easy to plonk on the garden table and impress Anyway, after all that, what exactly does a
mirror out of alignment, party guests with fi ne views of the Moon. Or you telescope do? Basically, it captures more light
and it will then need may want something more sturdy that can track than your eye – just think about the much larger
careful recalibration. the stars as they move across the night sky, so you diameter of a telescope tube compared to the pupil
• Tend to suffer from can photograph that distant galaxy ‘Slight Fuzz of your eye. By ‘playing’ correctly with this large
‘coma’, which makes stars
around the edge of the 7HX-67F’. But the two are quite different beasts, amount of light, the fainter objects of the Universe
view look triangular. and if you go out and make a purchase without can be revealed to us, and objects that are too small

HOW DOES A

TELESCOPE WORK? Starlight

Eyepiece
There are two basic Focal length
designs: one uses lenses, Focus
Primary
the other uses mirrors Lens mirror

PAUL WHITFIELD X2, PAUL WOOTTON REFRACTOR UPSIDE-DOWN IMAGE CORRECT IMAGE As well as magnifying

This type of telescope grabs all of its light
with a lens at one end of a tube. The light is
then focused down to the other end, where
distant objects, telescopes
an eyepiece magnifi es the image and
throws it into your eye.
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