Page 61 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

WHAT TO USE

The ‘W’ shape of
the constellation of
Cassiopeia as it appears
LARGE TELESCOPE to the naked eye
Bigger telescopes work with The large aperture of a Dobsonian
higher magnifi cations and narrow scope means that you can see stars and 0.5º
the fi elds of view further still, a result other objects as faint as mag. +14.0.
of their wider aperture. If you were Dobsonians, though, are not built to
to take a look at Cassiopeia using track (follow) the sky. They point at
an 8-inch Dobsonian fi tted with a the same fi xed spot. This means that
12mm Plössl lens, you would be you’ll see stars move across the sky
looking with a magnifi cation of as you look through the eyepiece.
over 100x that of your eye at an If your eyepiece increases the
angular fi eld of 0.5º. magnifi cation to a powerful 400x,
Our target is the open cluster things will move across your fi eld
called Messier 52 (M52). Through of view very fast indeed.
binoculars, this object is simply a faint
fuzzy patch. A small telescope
begins to resolve the individual stars
and shows its roundish appearance.
However, a big Dobsonian reveals a
fi ne group of about 200 stars with a
diameter of about 0.25º, which fi ts
easily into the fi eld of view. M52
sits within the Milky Way, so the Enjoy the full majesty of
surrounding sky is full of stars and M52 with a large telescope
other treasures to investigate.

1.3º

SMALL TELESCOPE You can split the beautiful double
To see more detail than you good example of this with mag. +7.4 star Achird with a small scope
get from binoculars you need a higher Achird (Eta (d) Cassiopeiae), a red star with
magnifi cation and an instrument that a brighter, mag. +3.0 yellow companion
captures more light. Welcome to the – though some people say the colours in
realm of the telescope. this double are more golden and purple.
Even with a small scope, like a 4-inch A small telescope will reveal objects
refractor fi tted with a 26mm Plössl lens, well into the 12th magnitude and, because
you’ll get a magnifi cation of almost 40x of its enhanced light-gathering power, things
greater than the eye. However, this comes like the shapes of nebulae and detail on
at the cost of a reduced angular fi eld of planets become apparent. Plus, for the fi rst
view, which goes down to about 1.3º. time in our equipment choices, you have
This kind of setup is useful for taking a look the option to increase the magnifi cation
at double stars. Cassiopeia provides a further by changing eyepieces.

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