Welcome back everyone.

So, in our last little discussion we talked

about just the basic idea of orders of magnitude.

And we've used five orders of magnitude in dollars to

understand how big a jump there was from a snickers

bar, which was one dollar, to a, a possibly a

nice apartment in Paris for hundreds of thousands of dollars.

And that was just five orders of magnitude.

Let's now apply that idea to astronomy, to

understand how we can move through different size scales

in the universe.

So let's start with our size scale

and we're going to be measuring things in meters.

Now again, remember that when we talk about orders of magnitude, what

we're talking about is you know, the general size of, of quantities.

So for example, I'm about two meters tall.

I'm a little bit shorter than two meters tall.

Like to be two meters tall, didn't quite work out that way.

But, I'm about two meters tall.

However, in terms of order of magnitude, I am ten to the zero meters, right.

That's about one meter.

I'm, you know, in terms of order of magnitude, I'm about one meter tall, okay.

So that's the size scale of a human, and

we'll use that as our reference frame for moving forward.

Now, the next large-scale, or, you know, important structure in

the universe, after us, and perhaps we shouldn't even use ourselves.

But you know were going to, we have to have

a reference so we'll use ourselves to begin with.

And the next step up in structure in the universe are planets.

And planets

as we have seen range in you know from our discovery range in

size scale from 10 to the 6 to 10 to the 7 meters.

So the difference in size scale between me and a

planet is larger, the jump in orders of magnitude is

larger than the jump from a snickers bar to you

know the really nice hotel or the nice apartment in Paris.

So that's just on the first leap in terms of size scale.

The next structure that we have to deal with in astronomy

are stars, and stars have size scales between say 10

to the eight and 10 to the 12 meters in scale.

So there are you know, dwarf stars and there are giant stars.

So, after stars, the next structure that we're interested in are

planetary systems, the collection of planets that are orbiting around stars.

So like our solar system, but we've also found other planetary

systems, and the typical size scales there are on the order

of 10 to the 13 meters, so that's a factor of 10

to a factor of 100 or even 1,000 larger than the stars themselves.

The next size scale we're interested in are galaxies, and

galaxies are vast collections of stars that exist in, they're

gravitationally bound, and the typical size scale for a galaxy

is on the order of, say, 10 to the 19 meters.

Now, notice what a jump there was between the previous size

scale, which was a solar system, and a galaxy.

And so what we're really seeing there is

approximately nine orders of magnitude from the coherent size

of a solar system to the collection of

solar systems or stars that go into a galaxy.

So there can, there's this enormous range of, of, of size scales that we're

dealing with in astronomy, and we haven't even gotten to the top in some sense.

The next size scale that we're interested in are galaxy clusters.

These are groups of galaxies.

And typical size scales there are a 1,000 times or more the size of the galaxies.

So 10 to the 22 meters.

And then finally we have the clusters, this, the super

clusters of galaxies which are clusters of clusters of galaxies.

And there the size scales are 10 to the 24 meters,

so even a thousand times, hundred times, or a thousand times more.

So, then we go all the way up to the size of the universe itself.

Now we can talk about the observable universe,

which is the, the sort of, bubble of

light that encompasses the universe that we can see.

But the thing that's important to understand is there

is most likely a lot more universe beyond even that.

So in some sense, well, according to

our best understanding, is that the universe right

now, our understanding tells us that the universe

is, in fact, infinite, on the largest scales.

Okay, so now we've done the large scales.

Now let's turn things around and go to the small scales.