Welcome to Learn the Sky, your online resource for learning about the stars and constellations.
Welcome, my name is Janine, and in this video we're going to take a look at the similarities
and differences between two stars. One known as Alpha Centauri, and the other is Beta Centauri,
both are part of the constellation known as Centaurus, which is represented as a centaur,
and these two stars right down here are the ones that we are going to look at for today.
So when we take a look at this picture I want your eyes to be drawn to the right side of the
photograph, and hopefully you can see the Southern Cross. The Southern Cross is what
you can use to find Centaurus, and the two stars that we are trying to point out, which are right
here. This one is Alpha Centauri, and this one is Beta Centauri, and if we were to point out
some of the constellations here and this is only a few of the constellations in this photo. I didn't
draw everything out, but here we have Centaurus, the Southern Cross, and Lupus is here as well,
and the two brightest stars in Centaurus are Alpha Centauri and Beta Centauri. Let's get a closer
look at these stars. So can you see the Southern Cross towards the right side of this photograph?
It's very easy to point out right there and you can use these two stars to guide you towards Alpha
Centauri and Beta Centauri. These two are often called the southern pointers because they can
help you find the South Celestial Pole. So we do have a video on Learn the Sky about the Southern
Cross, so be sure to go see that video if you want to learn more, but here is a diagram that shows you
how you can find the South Celestial Pole. You use the Southern Cross, draw an imaginary line down,
use the two southern pointers Alpha and Beta Centauri, and draw a line and it's very close to
the South Celestial Pole. So if we get a little bit more practice with this, here you can see the
Southern Cross right smack in the middle of the photo, from there are you able to find the southern
pointers Alpha and Beta Centauri? If you can then you can use it to find the South Celestial Pole. So
it's in this particular region. The South Celestial Pole doesn't have a distinct star right on it like
it does in the north with Polaris, but we can still use these stars as a guide to help us find
this location in the sky. I've got a few other pictures I wanted to show you because they're
so gorgeous and I have to share them with you, but here is a longer exposure photograph. So this is
where stars are taken, pictures of the stars are taken for a longer amount of time so they really
shine, and the brightest star in this photo is Alpha Centauri. Alpha Centauri is really special
because it's the closest star system to us. So if we were to point out Centaurus, that's where it is,
notice that the Southern Cross is in between the legs of Centaurus, and if we were to point
other things out this is what we have and this is what we would label everything. So as I move
forward and learn the sky I'm really excited to learn more about the Southern Constellations.
I myself live in the Northern Hemisphere so I mostly focus on those constellations,
but Centaurus is one that I've been studying and I've learned a lot about Alpha and Beta Centauri.
I've got one more picture for you, and hopefully at this point you're getting used
to identifying the Southern Cross as well as Alpha and Beta Centauri, and if we were to point it out
that's where Centaurus is and there's Alpha Centauri and Beta Centauri, and a fun little fact
this right here is a cool little globular cluster that can be seen with the unaided eye. So now we're
going to take a closer look at these star systems. First we'll start with Alpha Centauri, and Alpha
Centauri is a yellow main sequence star but it's not just one star it is a triple star system, and
it is the closest star system to our own. So it has some alternative names Rigel Kentaurus
is one of the names that's the main star called A, Tolimen is B, and then we have Proxima
Centauri. So if we were to show you what the size of these look like in comparison with our own sun,
this star system is very similar to our own in the sense that it's a yellow main sequence star,
just like ours. So here you can see this is Alpha Centauri, Alpha Centauri A, Alpha Centauri B, and
this is Proxima Centauri. So it's slightly bigger than the Sun, but not by much. Proxima Centauri
which is actually the closest star to us, not these two , and I'll show you a diagram to demonstrate
that, is a red dwarf star, so it is very tiny, and if we were to take a look at this picture
we have Alpha Centauri right here, this is Beta Centauri, and then there is a tiny little red dot
in the middle of this red circle and that is a red dwarf star, and that is Proxima Centauri.
So if we take a look at the distance to the Alpha Centauri system, here we have the Sun,
the Oort cloud, which is where comets originate from, and if we travel through right down here
you can see Proxima Centauri is slightly closer than the Alpha Centauri A and B star systems.
So now we will take a look at Beta Centauri. What's interesting is that Beta Centauri is
also a triple system, but the structure of it is is different. It's much farther away as well, it's
estimated to be 390 light years away and it has an alternative name of Hadar. It's an Arabic term that
means 'to be present', and there are three stars in this system. We have Beta Centauri Aa, Ab, and then
B. So they are all blue main sequence stars, but the size of them is slightly different.
Aa is about 12 solar masses, this is about 10 solar masses, and this is 4 solar
masses. So they are much much bigger than the Alpha Centauri system because they're
larger, they're hotter and they are a different color because they're hotter, they're blue.
So if we were to take a look at this system we would find that it's much much bigger than our
own, but the reason that it's dimmer than Alpha Centauri is because it's much further away.
In the next portion of this video we'll use a venn diagram to show the similarities and differences
between the two. I do this procedure with all of my versus videos because it gives a good idea of
how they're similar and different. So first we'll start with how they're similar. They're both in the
constellation Centaurus. They're both very bright stars. They're like in the top 15 brightest stars
in the sky, and they're both triple star systems, but they are each unique. Alpha Centauri is closer
in distance. It's only 4.37 light years away. It's also brighter than Beta Centauri, it's classified
as the fourth brightest star in the sky, and it has a magnitude of negative 0.7. Remember that
if a magnitude goes into the negative value it's brighter than one that would be positive. It's that
inverse relationship that we see with magnitude. I've got a video on it be sure to go see that. In
terms of color Alpha Centauri A and B are yellow, and then Proxima Centauri is red in color, and I
forgot to mention this in my last section that Alpha Centauri has confirmed exoplanets, and just
to get an idea again of what this system looks like Alpha Centauri A is the biggest, Centauri B is
the next biggest, and Proxima is a red dwarf star so it is very small in comparison to our own star.
If we look at Beta Centauri it's much further away at 390 light years away, it is slightly
dimmer it has a magnitude of 0.6 and it's the 12th brightest star in the star sky, but notice that
I did put that in here that they are both bright stars. So I'm being a little nitpicky here in terms
of their magnitude, and then the Beta Centauri system is all blue main sequence stars, and they
are of different size, but um keep in mind that the size comparison that I have here is not it's not
similar. These are much much bigger in size when you compare it, but I at least wanted you to see
how they're different in color and size in comparison to each other. So to wrap up this video
Alpha Centauri versus Beta Centauri. They are very easy stars to spot if you happen to be in an area
that has a latitude of 20 degrees North and below. If you live in the Southern Hemisphere you can
definitely see these two stars, and the best way to find Alpha Centauri in Beta Centauri is using the
Southern Cross. Use this portion of the cross draw an imaginary line across the sky, and you should
find these, and you know I have to share a small story. I only recently very like discovered these
stars in the night sky, um my last year when I was living in Hawaii I had an astronomy field trip
and I did not realize all these years that I was looking at Alpha Centauri and Beta Centauri.
I knew what the Southern Cross was, but I didn't really discover that the Southern Cross pointed
to these stars, and I literally I was on the astronomy trip and I'm like literally shouted
out to my students "that'sAalpha Centauri oh my god that's the closest star to us" and I was so
excited to just share it with my students at the time. So um I find it kind of silly of me that I
you know I've been studying the the sky for so long, yet it took me a really long time to find
the closest star to us, and but you know stargazing is always a journey and you're always going to see
something new when you go out. So to wrap up the similarities between these two is that
they're both in Centaurus, they're both triple star systems, and they're both very bright in the sky.
What's different is their color, their size, and their distance. So I hope this video was helpful
for you to understand the differences between these two stars and how to find them in the sky.
Always remember that it takes time, patience, and practice to really understand where everything is
located in the sky. So be patient with yourself, keep going out, seek out dark skies, and as always
keep looking up. If you're new to this channel be sure to click the subscribe button,
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in greater detail be sure to visit my website. I've got some freebies for you to download as
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