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.
As the fall season approaches the first thing I always look for in the autumn sky is the Great
Square of Pegasus, which you can see right here as I outline it for you. I've got a whole video
on this topic so be sure to go see that video, but in this video we're going to focus on some
unique celestial objects that exist within the boundaries of this constellation Pegasus. So,
Pegasus has some really cool galaxies to look at. It's got an awesome star cluster, but the really
fascinating object to me in this constellation is something known as Einstein's Cross, and
this is what's known as a cosmic mirage. So let's dive in and learn about what this phenomenon is.
So this cosmic barrage is a galaxy that is positioned in front of a distant quasar.
So this here is the spiral galaxy. You can see it, but right here in the center. What you
should notice is that the light is broken up into different distinct points, and this is an example
of gravitational lensing. This was an effect that Albert Einstein predicted as a consequence
of his theory of general relativity. So what's going on here is the light source in the cross
is it's about 10 billion light years away, so it's very far but the galaxy in front of
it is 10 times closer and that light from the quasar, which is behind the galaxy,
is being bent in its path and magnified by the gravitational field of the lensing galaxy.
So if we were to zoom into this area right here this is what you would see, and Hushra's lens
is the lensing galaxy of Einstein's cross. So this galaxy was named from
named for astronomer John Houstra, and here you can see that the lensed quasar looks like a cross,
and what's interesting is that the gravitational force from the galaxy creates four different
images of the quasar. So are you able to see this in the night sky? Well you cannot see it unless
you have magnification. Some amateur astronomers are able to point it out using telescopes,
but it would require extremely dark skies and you would need a telescope that has mirrors with
a diameter of 18 inches or more. So if we take a look at some other pictures of this, I really
love this one because you can clearly see those four points right there around that center part,
which is that gravitational lensing effect, yet you can see some other galaxies that are
here as well, and in fact the autumn season in the northern hemisphere is a great time
to look for galaxies because we are facing away from our own Milky Way galaxy, which allows those
other galaxies to shine through. Here we have just an arrow of me pointing it out to you,
but this is a really fascinating object and until I was researching Pegasus I didn't even know this
thing could exist and that's what I love about the field of astronomy is that there's always
something new to learn, and we've got one more final picture here of Einstein's Cross,
and we don't see the galaxy here because we're just simply zooming up on it, but there you have
it. So I challenge you to go outside if you happen to have a telescope with a diameter of 18 inches
or more. Yes, go see this if you have that type of telescope. You may even be aware of this object so
it's really fascinating. I hope I get to see it at some point in my lifetime. I'm more of a binocular
user than a telescope user, but this is such a fascinating object and I wish you luck trying to
find it. Remember you really need extremely dark skies, but even if you can't see it you can still
look in this area of pegasus in the sky look for the Great Square and just know when you're looking
in this region. There is a galaxy in front of a quasar and it's bending light and that is really
cool. So, thank you so much for watching. I hope you enjoyed this video about Einstein's Cross.
Let me know if you've ever seen it before, or if you know someone that's seen it, or if
it's something you hope to see in the future. Remember anytime you go outside it takes time,
patience, and practice, so keep going outside, be consistent with it, and as always keep looking up.