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Hello everyone, and welcome to week three of our course.
So, our question for this week is a big one.
How big is space and what fills it?
So this question of, you know, sort of does space go on forever
is sort of, you know, the one that we've all had as kids.
The history of astronomy is the history of
recognizing that the universe is is increasingly larger.
I don't mean that the universe is expanding.
We're going to see that it is, but just the recognition
that the, the what we consider to be the observable universe is
so much larger than our grandparents or great grandparents understood it to be.
So, you know, it used to be that space was pretty considered,
or the universe was considered, pretty much to be the solar system.
With sort of a sphere of stars around it
and then people recognize that no, no, no those
stars actually fill three dimensional space but they you
know, people were arguing about how big this collection
of stars were that we would call a galaxy.
And then at the beginning of the last century it was recognized that the
universe is actually full of many different
galaxies so it's been this ever expanding understanding
of the of the, how much space there is, how much matter there is, and
how this matter is distributed through space
so that's our question for this next week.
So the first thing to understand along these lines
is that there is no such thing as empty space.
All space has some
matter in it.
It could be just due to one hydrogen
atom per cubic centimeter or even less than that,
but you know, there is interstellar or intergalactic matter
distributed everywhere, so you know, you can see this.
If you get away from the cities and you get away
from the light pollution of cities you can actually see that the
sky is full of stars and if you get far enough away
where the sky becomes very dark, you can see that these stars
are not evenly distributed, but there is in fact, actually, a
band of both light and dark, which stretches across the sky.
And this is what we call the Milky Way, and it took a
while for people to understand, the, the true structure of the Milky Way, but
it was recognized that, that, that is actually a disk of, gas and
dust that, a Frisbee in some sense, that we are in the middle of.
Not in the, the geometric center of, but we
are a part of.
We're part in the the, the disk of the of the Milky Way.
We're going to see, as we study galaxies, what that means.
So we ourselves the solar system is part of a larger structure.
A city of stars, which we call a galaxy.
And then as we begin to study the sky in even more detail.
We recognize that there were other galaxies as well.
So, you know, here are some of
the questions we want to answer during this week.
What exists
between stars, in, within a galaxy?
And then when we start measuring the distances between
galaxies, we're going to have enormous distances to think about.
And how do we measure those enormous distances?
We can't put a tap ruler between the stars or, or certainly not between the galaxies.
So how do we measure these distances?
What is a galaxy and what different types of galaxies have
we found as we've explored this vastly enlarged space of the universe
that we've come to understand in the last hundred years?
What exists between galaxies?
Just as we've talked about what exists between stars.
What exists between galaxies?
Are there large scale structures that are even bigger than galaxies?
Do the galaxies themselves collect into even larger structures?
And if so, what fills up those structures as well?
So, these are our questions.
This is what we're going to be answering for the
next bunch of lectures or, or small sub-lectures, and
let's get started.
Adam FrankProfessor
