Today we are going to start our class. 
And, the best way to start a class on 
astronomy is to just go outside and take 
a look at the night sky see some of the 
objects we are going to talk about in 
their actual natural habitat so to speak. 
There's far too many of us to fit in one 
place and we are scattered too widely 
over the globe but through the wonders of 
technology I am going to invite you in a 
minute to do a virtual night sky tour 
with me and I encourage all of you to 
take either a virtual tour or even better 
if you can, to go outside and take a look 
up at the sky familiarity with the night 
sky is not the main object of this class, 
but it's a very pleasant side effect and 
I hope you'll enjoy it. 
So without further ado let me invite you 
to join me virtually in a. 
Field outside of Athens, Greece for 
definiteness. 
And we'll look up and see some of what we 
can see in the sky. 
Welcome to our observatory. 
We've chosen to locate ourselves in the 
outskirts of Athens, Greece. 
It is November 27th at 9 p.m. 
And when our software is simulating the 
sky and we're looking to the south, we 
have a very broad field of view of a full 
180 degrees. 
So we can see all the way from the. 
Eastern horizon to our left to the 
western horizon to our right, but because 
of the light pollution of a nearby city 
we see very few stars in the sky. 
This might be what you can see or it's 
certainly what I can see when I step 
outdoors. 
but the brightest stars in the sky are 
bright enough to shine against the glow. 
So we might see over here in the east 
Betelgeuse and Rigel. 
And perhaps Capella and Aldebaran. 
And over here on the western horizon, 
we'd see three very bright stars. 
Vega over here, Altair down there. 
And, Deneb over here, and these make up 
what is normally called the summer 
triangle. 
Let's step a little farther away from the 
city where more stars are visible, and 
try to get a better look. 
There, that's better with software it's 
much easier to turn off light pollution 
than it is in real life. 
And now we see the same view of the sky 
as it must have appeared before the 
advention of electric lights. 
And let's take a look and name some of 
the objects we see. 
over here, to the east we saw the two 
bright stars Betelgeuse and Rigel, which 
are now shown to be. 
Seen to be part of the famous 
constellation of Orion the hunter, 
there's his chest and his legs, his belt 
from which hangs his dagger, his club or 
bow over here, his outstretched arm. 
He even has a head up there and that 
would be Orion the hunter and Aldebaran 
will be part of Taurus the bull. 
There's his head and his body and there's 
long outstretched horns. 
looking further to the right we can 
identify some other famous groups there's 
W shaped objectives. 
associated with Cassiopeia, the vain 
queen. 
And not far from her, this great square 
of Pegasus. 
And from the great square Pegasus, 
towards Cassiopeia. 
These two streaming lines of stars, 
associated to Andromeda, Cassiopeia's 
daughter. 
And up here Vega, the bright star we saw 
in the western sky is part, in fact, of 
Orpheo's lyre. 
This is the constellation Lyra. 
And finally, 
my favorite constellation we talked about 
Deneb over here. 
And Deneb is just the tail of Signus the 
swan. 
There's his tail and severed his heart, 
and a long swan neck that ends at 
Albireo, his head. 
And his pretty swept back swan wings, you 
can certainly see a swan. 
There are many other constellations but I 
don't have time to show them all. 
Let's allow the software to do that for 
us. 
Here that the software designate for us 
the. 
most famous of the constellations. 
And the brightest stars that comprise the 
shape or the asterism of the 
constellation. 
And we see Orion the hunter, and Taurus 
the bull, and Pegasus, the flying horse, 
and so on. 
As well as many others. 
And what we recognize is that many of 
them have their origin in Greek 
mythology, at least in the northern 
hemisphere. 
The reason for this is, 
and the point I'm trying to make with 
this image is, that if you show this 
picture without the helpful blue lines, 
to someone who lived in Athens thousands 
of years ago. 
I don't know, the philosopher Aristotle, 
he would not only recognize the stars, he 
would name the constellations and he'd 
use the same names that we use, because 
the pattern of the sky as Aristotle saw 
it on a fall day in Athens 2000 years ago 
would be extraordinarily similar, 
essentially identical to what we see 
today, absent light pollution. 
There is this beautiful permanence in the 
sky. 
The stars that we see today are 
essentially the same as they've always 
been. 
And this is something that has made 
astronomy one of the oldest sciences. 
It's also something we can use to 
establish a geography of the sky, so 
that, if I want to describe, or if an 
astronomer wants to describe viewing an 
object that lies right here, even if it's 
not part of the asterism of Orion, he 
would say, the star lies in the 
constellation Orion. 
Astronomers have formalized this by in 
recent memory actually dividing the sky 
into 88 regions. 
In the Northern hemisphere they're 
associated to ancient Greek 
constellations for the most part, and so 
now we precisely can distinguish a star 
that lies in the constellation Orion from 
some nearby star that lies in Taurus. 
And when we talk about stars lying in one 
constellation or the other I will be 
referring to this 
the treaty, that divides the sky into the 
88 constellations up, 
the point that this again is trying to 
remind us of is that, a star that is in 
Orion now will be in Orion a century 
hence, and so there's this geography that 
we set up and we can identify positions 
in the sky. 
Removing for a moment all the distracting 
lines that the software was drawing, 
let's take a closer look at some of the 
objects we're seeing and try to pay 
attention again to what we're seeing. 
So we see large numbers of stars. 
We noticed that they were different 
colors. 
Some of them were more reddish or 
orange-ish or yellow and some are blue. 
The colors of stars are in themselves an 
interesting topic. 
We'll talk about that. 
the distribution of stars is interesting. 
If you look, you'll see that there are 
less stars here or here than there are 
along this region of the sky. 
This stripe through the sky and in fact, 
if we look closely, we'll see that even 
in between the stars the sky here is 
brighter than elsewhere. 
This is, of course, the famous stripe of 
the milky way. 
We'll want to take a close look at that. 
Here's what part of the Milky Way looks 
when you take a slightly long exposure 
photograph. 
The exposure brings out many, many stars 
an we see that this bright stripe in the 
sky that I call the Milky Way. 
has a lot more structure. 
It's not just a white stripe. 
There are these darker areas and brighter 
areas. 
Different colors, lots of stars. 
We'll take a close look at that and try 
to understand what the Milky Way is. 
There are some other objects visible in 
the sky that will justify a closer look 
of the form that Aristotle would not have 
been able to take advantage of. 
if we look at Orion here, and if we look 
at the stars, the three stars that form 
the dagger dangling from Orion's belt, 
then suddenly the middle one it's pretty 
clear, does not really look right. 
There's something fuzzy about that star. 
we'll take out a telescope and get a 
closer look at that. 
The slightly fuzzy suspicious star in the 
center of Orion's dagger that we 
mentioned turns out in a moderate 
telescope to be a lot more interesting 
than you'll think. 
In fact all of this stuff all of these 
stars all of this nebulous scattered 
light blue and pink these darker regions 
all of this is what our eyes sees as a 
slightly fuzzy star. 
And, understanding what is going on in 
the Orion nebula is going to be something 
that'll be very exciting for us. 
Slightly farther south, over here, just 
past Taurus, and in the constellation 
Taurus in particular, is this wierd 
collection of stars. 
A whole bunch of stars clustered together 
very close. 
The collection of seven bright stars in 
the constellation Taurus. 
Traditionally called the Pleiades, in 
some cultures. 
The Seven Sisters. 
different names for this obvious bright 
collection. 
Here are the seven bright stars. 
We see that there are many others near 
them, just not bright enough for us to 
see. 
And, even again, as in Orion we see that 
there is this nebulous stuff, there's 
this blue shiny stuff that is not a star, 
that is producing light. 
So some of the light we see is not coming 
from the stars at all. 
And if we look at this collection of 
stars, then perhaps it's worth looking, 
just below Pegasus over here. 
If we looked very closely, there would be 
a faint and slightly fuzzy object, 
probably better seen with a telescope 
than the naked eye. 
In a moderate telescope, the group, 
slightly faint, fuzzy object in the 
constellation Pegasus that I mentioned 
turns out to be this beautiful, globular 
cluster called M13. 
again we see many, many, many stars, far 
more in fact than in the Pleiades. 
We also see that they're all dimmer the 
stars in the Pleiades were bright like 
this. 
These are dimmer objects, and they also 
appear to be very much more tightly 
clustered. 
In a constellation of Andromeda up here 
in between 
Pegasus and Cassiopeia. 
If we look around here, there's another 
one of those fuzzy objects. 
Suspiciously, not quite starlight. 
If you magnify it a little bit and 
collect light for a long time and process 
carefully, turns out to be this 
beautiful, richly structured object, the 
great spiral galaxy Andromeda. 
I should point out that the fuzziness 
that we see, is only the brightest 
central part of this. 
This object itself is about five times 
the size of the full moon in the sky. 
It's very large and very, very faint, and 
requires careful image processing and 
light collection to get all this 
structure out. 
But nevertheless, our eyes without 
misleading us, there's something 
interesting there certainly worth 
investigating. 
Farther to the west. 
Remember the bright star Vega in the 
constellation Lyra. 
If you look over here in Lyra, we'll see 
with a telescope a faint fuzzy object. 
The slightly fuzzy object in the 
constellation Lyra that we saw, with a 
moderate telescope turns out to be this 
beautiful ring shaped, nebulous light. 
lots of fun colors in this and 
understanding what this ring structures 
is will be a lot of fun for us as we go 
along. 
And finally, we'll take a close look at 
this moderately bright star Albireo, the 
head of Cygnus the Swan. 
when you look at it more closely, turns 
out to be not one but two stars of 
differing brightnesses, there's a bright 
and a dimmer star, and of completely 
different colors. 
One of these is orange, the other is 
described by various people as being 
either. 
Purple or blue or green, but certainly 
these two stars are very obviously 
different colours. 
Understanding why stars come in different 
colours, what these two have to do with 
each other, will be another topic we'll 
spend some time on. 
Hope you enjoyed the little preview of 
all the things that we can see that poor 
Aristotle could not because he did not 
have telescopes. 
Let's go back to what it is that 
Aristotle did see. 
I've made a big deal of the fact that the 
sky is unchanging. 
But in a sense I was cheating all the 
time we've been talking it's still 9 p.m. 
in our simulation. 
I'm now going to let time move at a 
somewhat accelerated pace and then we 
will see. 
That the sky is not in fact unchanging, 
things move. 
Orion is clearly moving from low in the 
eastern horizon, to high in the south and 
eventually will set in the west, But 
things maintain their shape, the motion 
is not random, the motion is rigid. 
Of course pretty soon, the sun will rise 
and we might as well stop observing. 
So let's collect ourselves after a good 
hot cup of strong Greek coffee, and 
summarize what it is we've learned. 
Back from our night under the stars, 
hopefully all energized and excited to 
understand all the things that we've 
looked at. 
Let's see what it is that I was trying to 
make clear from these observations. 
we saw that we see many, many stars. 
We can see as many as 3,000 at a time on 
a clear night. 
And we saw that we named the groupings by 
ancient Greek names because the pattern 
that we see in the sky is unchanging. 
We also watched the sky move, but we 
noticed that the motion was a rigid 
motion. 
Betelgeuse and Rigel remain in the same 
relative position. 
They're both in Orion in the same 
relative position throughout the motion 
of the sky. 
And in fact they have been in that 
position since humans started observing 
them. 
So we can set up a geography of the sky. 
We can declare some part of the sky to be 
Orion, and another part of the sky to be 
Cygnus. 
And this is a meaningful thing despite or 
throughout the motion of the sky. 
that said, the sky moves. 
Everything rises in the east and sets in 
the west. 
So what you see in the sky at any given 
time is not of constant time. 
And our job for the rest of this week is 
going to be to understand and 
mathematically describe, at some level of 
precision, this motion and this 
permanence and how we can predict what it 
is that we will see, looking up from 
Athens at 9 p.m. 
in what direction in the sky.