As you look at this photo what are some of the things that you notice about these clusters of
stars? For me I noticed that the color is different. Here you see more white and yellow stars, where
here you see mostly blue stars. The shape of the clusters are different, and the number of stars
are different. This cluster right here has a lot fewer stars than this here, and essentially those
three things the shape, the number of stars, and the color are the characteristics that we use
to classify stars among other characteristics, and in this video we're going to explore the
similarities and differences between open and globular star clusters. Welcome to Learn the
Sky, my name is Janine and I'll be your guide as we explore the sky one constellation at a time.
First we'll examine the characteristics of open star clusters. An open star cluster has
no defined shape, and in terms of number of stars it can be a dozen of stars, to up to
a hundred, or even thousands of stars. In this particular photo we're looking at the Pleiades,
which can be seen with the naked eye, and we see usually six or seven main stars here, but in
reality there's almost a thousand stars here and its age for open star clusters typically tends to
be in the millions of years, and these stars that we see in open star clusters are typically young,
hot, and blue stars. Their location in the galaxy is typically found in the disc, or the arms of
the Milky Way galaxy. So what does that mean? If we look at the shape, this is a very simple
drawing of our galaxy. So here would be the disc of the galaxy, remember we're a
spiral galaxy, there's the core of the galaxy, we're located about two thirds of the way out
from the core of the galaxy, and where we find open star clusters is in this band right here,
okay. Globular clusters are typically in another region in our galaxy above and below, and they
kind of circle around the core of our galaxy, but open star clusters are right within the disk, and
if we were to actually kind of use a picture of the Milky Way, right here in this disk area
is where open star clusters would be located. Up in this region is where you find globular star
clusters. So the distances of open star clusters are typically, they're usually closer to us than
the globular star clusters. So I wanted to give you some previews as to what are some open clusters
I can see with the naked eye, or if you have pair of binoculars it helps to take a look at
them as well, or even if you have a telescope, whichever type of observer you are. Right now
I just mostly work with binoculars, that's what works for me at this point in time,
and here we have the Pleiades, which I showed you earlier, and this is the Hyades, and these
are two open star clusters that are located in the constellation known as Taurus. I have a whole video
about Taurus, so if you want to learn more about that constellation go see that video, and if we
were to zoom up on the Pleiades, oh and before I zoom in this is also an asterism together known
as the Golden Gate of the Ecliptic. That's a recent discovery of mine I love learning about it, but it
was called that because the Sun, Moon, and Stars would pass through here, and it's kind of like
you know like a gateway. So very cool, and if we were to zoom in this is the Pleiades, right here.
You can see no definitive shape, but some say it looks like a little dipper, which you
know I definitely would agree with that, sometimes people think this is the little dipper. I've got a
video on the Pleiades, so go ahead and see that video, and here are the Hyades. The Hyades is a
very well studied star cluster. It's only about 150 light years away. This star right here is Aldebaran,
and not really a part of the open star cluster, but this makes up the face of the bull of Taurus.
So it's one that definitely can be seen with the unaided eye. Some other examples of open star
clusters include the Beehive Cluster in Cancer, also known as Messier 44. This is what it looks
like if we were to zoom in, and here it is zoomed in even more. So again no definitive shape here,
most of the stars here are blue which will tell will give us those, the color of the
stars really gives us some insight into the age of a star. Some other examples
include Messier 6, and this is in Scorpius. We have Messier 7, this is also in Scorpius.
These two can be seen with the unaided eye if you live in dark sky areas. Here's another version,
like you know the 'expectations versus reality,' this is more on the expectation side of that meme.
The Ptolemy cluster is a really great one that you can see in Scorpius, and now I jumped ahead. So
let's get into it. Globular star clusters... These are spheroidal shaped star clusters, and they
have typically thousands to millions of stars. So as you're looking at this photo, and I'm describing
what globular star clusters are hopefully you can point out two in this photo. These types of stars
are typically billions of years old. They are metal poor, and their location in the galaxy is different
than open star clusters. They're in the halo of the galaxy. They orbit around the galactic center. So
here you can see Messier 80 and Messier 40, and this is near Antares. So that's the heart of the
Scorpion, I've got a whole video on Scorpius so go see that, and again just to review where its
location would be in the galaxy the globular star clusters orbit around the galactic center, okay,
and they're typically farther away in distance. So again just this same photo you saw before here in
this region is where you would find globular star clusters. You don't find them in the band of the
Milky Way galaxy. Some examples of globular star clusters include Omega Centauri, this is a globular
star cluster. It's 15 000 light years away, so much farther than say the Hyades or the Pleiades.
Here's a zoomed up version of this. I just love that photo, and you can see there's a high
density of stars in the center and then it gets thinner as it as you move away from the center,
and there's just a lot a lot more stars here than in open star clusters. So it makes it really easy
to identify the differences between these two. Some of the famous globular clusters are Messier
13, that's in Hercules as well as messier 2, also in Hercules. So you want to just notice that shape.
They really have that, to us it's like a circle you know, but in 3d it's like a sphere shape. So let's
wrap this video up by going over our venn diagram, which we look at the similarities and differences
between these two. I always do this practice for my versus video. So first they're both star clusters,
they are both groups of stars that are bound by gravity, and also traveling together, and they
can be seen with the unaided eye, except you know when you get these fantastic pictures. That's not
something, you know you need a a expert telescope to to capture something like this.
So definitely need equipment there. So that's how they're similar, but in terms of their differences
there's a lot of them. Open star clusters have no shape, they're typically closer to us, they're
less massive, they're younger in age on the order of millions of years with these hot blue stars,
and they are located in the disk of the galaxy, and they typically have gas and dust within
the open star clusters, but globular star clusters their shape is different. They're spheroidal in
shape, stars are concentrated towards the middle of that shape, and they're tens of thousands of
light years away, and we can actually see these in other galaxies which is really really
amazing. So we're able to study the motion and the number of globular clusters around other galaxies.
Globular clusters are more massive, from thousands to millions of stars, they're older, and they also
are located around the halo of the galaxy as it goes around the galactic center. So I hope
this was really helpful for you in learning the differences between these groups of star clusters.
Open star clusters, right here you can see there's gas and dust there, no shape, to this picture
it looks like there's a few dozen, but in reality there's over a thousand
stars here that are bound together by gravity, and they're traveling together, and there can be some
that can be visible with the naked eye. Those are the ones I reviewed with you in this video.
So the way that they're different are their shapes, their ages, location in the galaxy, as
well as their distance. So I encourage you go back through this video, write down those different
objects that you can try to find in the sky, just to hopefully you can see
for yourself the differences between the open star clusters as well as the globular star clusters.
Remember it takes time, patience, and practice, so keep going outside and as always keep looking up.