Page 73 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

WHAT TO SEE

to tremendously destructive
stellar explosions called novae.
Of course, you won’t see any
of this going on when you look
through a telescope, but double
stars are still amazing targets
to aim at. Some doubles show
startling colour differences
between the two stars – you
may see, for example, a
shimmering yellow star next
to a vivid blue one – while with
other double stars, the two
will be more or less the same
brightness, yet sit startlingly
close together. If you can spot
our top fi ve favourite doubles,
which we’ve listed below, we
have no doubt that you’ll soon
be hooked on these jewels of the
night sky. Albireo is a beautiful binary star with striking gold and blue components

TESTING YOUR SCOPE

You can use double stars to test your
telescope’s optics. How well you can
split the stars depends on the quality of
your optics, as well as the size of your
telescope’s aperture, or front lens.
If you have a good-quality small
telescope, say four inches in diameter,
you should be able to see doubles up
to 1.15 arcseconds apart, if seeing
conditions are perfect. Our top fi ve
doubles on the left should all be easily
within your reach.
5. PHAEO To split double stars closer than this,
you need a larger telescope. To fi nd out the
AND PHAESYLA closest double stars a telescope will theoretically
Constellation: Taurus split, you just divide 4.6 by the diameter of the
This orange and white optical telescope’s front lens in inches. It’s a theoretical fi gure,
double is easily visible to the though, because if the atmosphere is fairly turbulent
naked eye, with mags +3.8 and then you won’t be able to see the components of a
+3.4 respectively. Also called really close double star as well.
Theta Tauri, it is part of the
Hyades star cluster.
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