Page 60 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

KNOW YOUR

FIELD OF VIEW

DIFFERENT EQUIPMENT WILL SHOW YOU DIFFERENT PORTIONS
OF THE SKY, BUT WHAT’S BEST FOR YOUR CHOSEN TARGET?

When you’re out stargazing, the fi eld of
view is the amount of sky that you can THE NAKED EYE
see at any one time. It varies depending Your eyes are excellent for expansive views of the
on what equipment you’re using – here constellations, asterisms, meteor showers, the Milky Way and
we show you how the appearance of the big bright comets. Of course, you can see other objects, but it’s
the general majesty of the heavens that you get with such an
constellation of Cassiopeia changes
amazing, near-180° left-to-right fi eld of view. It makes the naked
when you look through different eye an enjoyable means of looking at the night sky. The main
types of instrument. image here shows what the constellation of Cassiopeia looks
like to the naked eye.
It’s said that the eye has a magnifi cation of 1x and the faintest
stars you can see are mag. +6.0. Some people have claimed
to be able to see stars as dim as mag. +7.0; even if you can,
you’ll still miss nearly all of the wondrous deep-sky objects
and any hint of their structure. For these objects you need a
pair of binoculars or a telescope.

JERRY LODRIGUSS/SCIENCE PHOTO LIBRARY, ROBERT GENDLER/SCIENCE PHOTO LIBRARY, WILL GATER, PETE LAWRENCE

BINOCULARS 9º
Using a standard pair of
10x50 binoculars you instantly
increase your magnifi cation to 10x,
meaning things look 10 times bigger. The Double Cluster looks
Also, instead of the standard 5-7mm great through binoculars
width of your pupils, you have the
binocular’s 50mm-diameter lenses to collect starlight. This
allows you to see faint stars deep into mag. +10.0 territory.
Depending on the make, 10x50 binoculars have a fi eld of
view between 5º and 9º. This gives you lovely wide views to
sweep across the sky in search of objects like nebulae, galaxies
and star clusters, which look great through binoculars.
Just outside Cassiopeia there’s something well worth
viewing with binoculars, the Double Cluster in the constellation
of Perseus. With the naked eye, you can just make it out as a
faint smudge. Binoculars, though, reveal it as a true marvel:
hundreds of stars in two distinct clusters spanning an area
about 1º across. It’s a stunning sight that easily fi ts into the
fi eld of view of a pair of 10x50 binoculars.

60 skyatnightmagazine.com 2012