Welcome to Learn the Sky, your online
resource for learning about the stars.
Learn the Sky is now on Patreon, so if
you would like to support this channel
in order to learn more about the sky,
please visit our Patreon account, the
link is listed below.
We are also offering new online courses,
so if you're interested in learning
about the sky in greater detail and
would like a guide to help you walk
through the sky, please visit learnthesky.com
and check out our online courses.
Welcome! My name is Janine and in this
video we will explore the constellation
known as Pegasus. First let's look at
some of the mythologies that surround
this constellation. In Greek mythology,
Pegasus is a winged horse who is the son
of the mortal Medusa and Poseidon when
Perseus beheaded Medusa, Pegasus and his brother emerged from her neck. Once born
he was taken in by the muses of Mount
Olympus and raised there. One story of
Pegasus traces back to the Greek hero
named Bellerophon. He captured Pegasus
and rode him in his fight with the
Chimera. It was said that Bellerophon
attempted to fly with Pegasus to join
the gods, but fell back to earth. Pegasus,
however, made the journey, then becoming a constellation and the servant of Zeus.
There are multiple myths and legends
about Pegasus and they vary from culture
to culture just like many of the
constellation stories.
Now let's identify the distinctive pattern of Pegasus. The most obvious feature of Pegasus is the
Great Square which is outlined here this
shape dominates the sky in the autumn
and it takes up a fairly large portion
of the sky. This shape is also identified
as the asterism called the Great Square
of Pegasus. Remember an asterism is not a
true constellation but rather an
easy-to-find shape within larger
constellations. They can be used as
markers to help us find our way around
the sky. So here is a portion of the
constellation Pegasus and it represents
a winged horse and is classified as a
seasonal constellation.
Now Pegasus is a difficult
constellation to get in a photograph
because it is so large, but here you can
see the Great Square of Pegasus and then
the head comes off this way and two of
the legs this way.
Here is a picture of Pegasus that I took with my camera phone
and while the quality of it isn't that
great it's a good photo because it does
show the entire constellation of Pegasus.
So before I point it out for you, are you
able to identify the Great Square
asterism that's right in the center of
the photo? If you can, then you should be
able to find the rest of the
constellation so here it is we've got
the great square right in the center and
then the head that jets off right here
and the two legs right here. Now Pegasus
does share a star with the constellation
Andromeda, so you can start to see that
constellation come off the Great Square as well.
Now that we know the pattern of
Pegasus let's take a look at the bright
stars that sit within its boundaries. So
as we take a look at the official star
map of Pegasus, you hopefully can
identify the Great Square, the two legs
and then the head. The brightest stars
are seated within the Great Square, so
let's take a look and zoom in there. The
Alpha star is known as Markab, and
it's an Arabic name that means 'saddle of
the horse.' Alpha Pegasi is a B type giant
star which means that its core has run
out of hydrogen and it's beginning to
evolve beyond the main sequence phase of a star. It's in the southwest corner of
the Great Square and is estimated to be
133 light-years from Earth. So here is a
picture of the Great Square and
hopefully you can see it right in the
center. This is where Markab is.
Beta Pegasi also names Scheat, is a
red giant star and the second brightest
star in the constellation of Pegasus. It's
name is Arabic for 'upper arm' and it
forms the upper right corner of the
Great Square. It's luminosity is 1500
times that of our own Sun.
Algenib is the gamma star of this
constellation. Its name is Arabic for the
flank and it is a large star with almost
nine times the mass of the Sun and close
to five times the sun's radius. This star
has also run out of hydrogen and is
starting to evolve out of the main
sequence phase.
Now let's examine the celestial objects that sit within the boundaries of Pegasus.
There's a galaxy, a globular cluster and a cosmic mirage known as Einstein's Cross.
First let's take a look at NGC 7331. It is a
cluster of galaxies, but the main one is
this large spiral galaxy to the right of
the image and it's often referred to as
Milky Way's twin because it's very
similar in structure. There are a few
other satellite galaxies that surround
this larger galaxy and if we zoom in
here you can see it's an unbarred spiral
galaxy and it's estimated to be 40
million light years away.
Messier 15 is a globular cluster that
sits within the boundaries of Pegasus. It
is estimated to be thirty three thousand
six hundred light years away and it is
one of the most densely packed globular
clusters known in the Milky Way galaxy.
It is also one of the oldest; it has an
estimated age of twelve to thirteen
billion years old and it contains over
100 thousand stars.
Huchra's Lens is the name of the lensing
galaxy that's in front of the Einstein Cross.
The galaxy is named for astronomer John Huchra. Here you can see that the
lensed quasar resembles a cross. So the
gravitational force from the galaxy
creates four images of the quasar behind
it. Amateur astronomers would be able to
see some of the cross using telescopes
but it would require extremely dark
skies and telescope mirrors with
diameters of eighteen inches or more.
Let's review what we've learned about
Pegasus the winged horse constellation.
It is best seen in the autumn months and
it's classified as a seasonal
constellation. The best way to find it is
to look for the asterism known as the
Great Square of Pegasus which takes up a really large portion of the sky. In terms
of celestial objects that contains a few
galaxies, a globular cluster known as
Messier 15 and a cosmic mirage known as Einstein's Cross. I wish you luck finding
this constellation and if you have any
questions or comments be sure to leave
them in the spot below. I also want to
send a huge thank you to David Cocklin
for allowing me to use his amazing
photographs for my videos. Be sure to
check him out on Twitter. Good luck
finding Pegasus!
 
 
