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Hi, this is Phil Plait - The Bad Astronomer - and you are watching Sirius Stargazing.
Welcome to Sirius Stargazing. I'm TK and in this episode we're going to look at the beautiful
Pleiades Open Cluster, easily one of the finest things in the whole sky to see through binoculars,
and in fact many astronomers would agree that it actually looks better in binoculars than
it does through a telescope, thanks to the wide field-of-view. In 1771, the French astronomer
Charles Messier included the Pleiades cluster in the first version of his catalogue of deep-sky
objects, and today astronomers often refer to it as Messier 45, or M45 for short, but
it's much more commonly known as the Seven Sisters. Whilst you can almost always see
6 or 7 stars with the unaided eye, there are in fact 10 very bright named stars in the
group. Asterope is actually two stars close together, and aside from the sisters are their
parents, Atlas and Plione. Together they make a shape quite reminiscent of a little dipper,
with the parents as the handle and the daughters as the bowl. Beyond these 10 very bright stars,
there are actually over 1,000 members in the cluster, but the bright central region is
easily breathtaking enough on its own. What you're seeing, like all open clusters, is
actually a remnant of a stellar nursery, or a dense nebula where many stars formed close
together. The brightest are all hot, blue stars, and they're all less than 100 million
years old. That might sound like a lot, but that's actually very young for a star. They've
since blown away all the remaining gas and dust from the nebula that they formed from,
but if you were to take a long-exposure picture of the Pleiades, you would see nebulosity
around them, and it looks like this. It appears because the cluster is passing through another
nebula, and the starlight is reflected by it, causing it to glow. This is known as a
Reflection Nebula, and in theory it is possible to see a very faint hint of this through binoculars;
a few hundred years ago, astronomers reported seeing it through telescopes as small as 2
inches. Unfortunately the increase in dust and light pollution in the atmosphere has
made it virtually impossible today, and this is one of the sad reasons that we should be
working to preserve the natural beauty of the night sky. At about 440 light-years away,
the Pleiades is easily one of the nearest star clusters, and definitely the most conspicuous
in the sky. You won't have much trouble finding it. It marks the shoulder of Taurus the bull,
so use your planisphere to work out what time Taurus will be reasonably high above the horizon,
and when you go out M45 will be one of the most striking things that you'll see, even
if there's a fair amount of light pollution around. Once you've got used to training your
binoculars on the cluster, here are a few challenges for you. Firstly, you shouldn't
have too much trouble separating the two stars that make up Asterope. Resolving both members
of a double star, or seeing two stars that appear very close together, is known as 'splitting'.
Once you've split Asterope, try to resolve this star next to Alcyone. It's actually the
brightest of several companions to the Pleiad, but it will be a challenge to see next to
the brilliance of Alcyone itself. You'll have to hold your binoculars very steady, and it
might help to buy a tripod adapter and attach them to a camera stand. If you can get both
of those and the conditions are really, really good, then have a look for the two dim stars
right in the centre of the bowl. It's a real challenge to split this double, and if you
manage it with binoculars, you can be sure that you have excellent visual acuity. So,
good luck! The best time to see the cluster is during the Winter months, so make sure
you wrap up warm if you're going out to look at it. When you are looking at it, consider
that you're seeing the stars as they were before the invention of the telescope. All
of modern astronomy, right up to you looking through your binoculars, has occurred since
the light left those stars on its journey to your eyes. Until next time, clear skies.