Hi! Welcome to Learn the Sky, my name is Janine and in this video I'm gonna walk
you through the difference between globular star clusters and open star
clusters. If you are outside on a clear and very dark night you may start to
notice that there are certain parts of the sky that can appear a bit fuzzy to
the naked eye. It's very possible that what you are looking at can be a star
cluster, and sometimes it's the best to examine these little fuzzy patches of
light with some sort of magnification, whether it be binoculars or a telescope.
So let's take a look at the two different types of star clusters. We have
globular clusters and open star clusters, and just by looking at these different
types of pictures it's pretty obvious how each got their names. Globular
clusters are these spheroidal, ball shaped groups of stars, while open
clusters do not really have a definitive shape, but there really is much more to
these grouping of stars than just their shape. Globular star clusters, as I have
mentioned before, are these spheroidal shaped groups of stars and they can
contain between thousands of stars and up to millions of stars, and they're
typically few hundred light-years across, and they often live within the
halo of our galaxy, which really means that they're orbiting the galactic
center. They're not really located within the arms of the galaxy and these star
clusters are very very old. They're often between twelve to thirteen billion years
old, sometimes a little younger and the stars that are located within globular
clusters are known as first generation stars, so they have been around for a
very long time, so typically you the red giant stars and supergiant stars,
and since they're very old it takes a long time for them to form, and sometimes
a few of them have formed within the cores of smaller galaxies that have been
cannibalized by the Milky Way. So let's take a look at where we're gonna find
this, here is a depiction of what our galaxy looks like, and we have the
nucleus of the galaxy here, and then we have the spiral arms that are coming out.
The globular star clusters are really situated on outer edges of the galaxy, so
that's located within the halo of the galaxy, so now that you know what a
globular cluster is, where in the sky can you find one? One of the brightest
globular clusters that's visible in the northern hemisphere is known as Messier
13, and it is located very close to the keystone within Hercules, and to the
naked eye it appears to be a fuzzy patch, but with the telescope or binoculars it
can be seen much more clearly. This cluster is estimated to be 145
light-years across, and contain over 300,000 stars and its distance is
estimated to be 25,100 light-years away, and its age is very old,
estimated to be around 11.5 billion years old. Now keep in mind that when you
identify this cluster in the sky with some magnification it won't quite look
this magnificent, this picture was taken with a high-powered professional
scientific telescope, but even so if you're able to find it it's really easy
to just appreciate the beauty of this particular globular cluster. Now that we
reviewed globular clusters let's review the differences between them and open
clusters. So open clusters are often open, and very loose grouping of stars. They
can contain a few dozen stars, or even thousands of them, and sometimes they can
be compact, or they're loosely grouped, but what's unique about them is that
they're found within the disk of the galaxy, and they're pretty young, they're
on the order of millions, to maybe a few billions years old, but they definitely
don't show the age that globular clusters have, and these stars are
different in the sense that they are second-generation stars, so they have
formed out of stars that have previously lived and died, so when you're looking at
them often they contain hot and blue stars. So let's look at their location
within the galaxy, if we look at this picture right here, here's the disk of
the Milky Way, here is the nucleus, and here's what's considered the halo, okay,
if we're looking at the Sun we're about two-thirds of the way out from the
center of the galaxy, but open star clusters are only found within the disk
of the galaxy. So now that you know what an open star cluster is let's take a
look at a prime example of one. Messier 45 known as the Pleiades, or the Seven
Sisters, or Subaru when you look at the Japanese culture, is very famous, one
because it's very easily identified with the naked eye, and two because it's just
one of those really really beautiful star clusters, and it's fairly close to
us in terms of the size of the universe, it's only 415 light-years away, and when
you're looking at the main stars located right here, it's about eight light-years
across, but in reality there's over a thousand
stars within this cluster. It's age is fairly young too, when you look at the
age of the universe. This star cluster is about 115 million years old. So when
you're looking at this one for the naked eye, where are you
gonna find it? Well you have to look to Taurus. So Taurus is right here, and
here's the v-shaped face of the bull with its horns protruding out, and then
the Pleiades is located right here in the shoulder of the bull, and what you
want to look for is a small little tiny grouping of about six stars, but when you
magnify it this is what you end up seeing. Now of course you may not see all
the different nebulosity that is seen in this picture because this is taken again
with a very high-powered telescope, but it's really easy to identify, so I
challenge you to go outside locate Taurus by using Orion, here's Orion use
the belt stars, follow it up to the v-shape face, and then you should be able to find
this very famous star cluster, and this particular cluster was very helpful for
those ocean faring navigators. It was used to help determine when it would be
the best time to sail upon the different seas, and there's many many unique
stories surrounding this cluster which I won't really go through in this video,
you can check out other videos of mine for that, but again if you're trying to
look for an open star cluster this is your prime example, because not only can
you see it with the naked eye but it's also very beautiful with magnification.
So just to recap, globular clusters are known as ball shaped groups of stars
that are very old and aged, in the order of billions of years old, they are larger
in diameter, they contain first generation stars that evolved into red
Giants and supergiant's, and they live within the halo of our galaxy. Open star
clusters do not have a definitive shape, they are younger, they contain
second-generation stars which are often hot and blue and they live within the
disk of our galaxy. I encourage you to go outside and continue to observe what you
see, and see if you're able to locate any of
these amazing clusters, and if you can feel free to share what you saw in the
comments listed below. So thanks so much for watching, and remember continue to go
outside. keep looking up. and share what you have learned and observed with
others about the stars.