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.