The big question for this segment is, how do we know how stars form?
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Everything we can learn about the universe depends on just detecting photons
by our telescopes here on the ground, on Earth, or via our satellites in space.
So everything we do, and everything we understand about our universe and
our place in it, is a combination of both these kinds of observations, and
the theory that backs up these observations.
It's about only 400 years ago that Galileo Galilei first used
a rudimentary telescope.
He actually, this is a myth, he didn't invent the telescope himself.
He used the design of a Dutch instrument maker called Hans Lipperhey to actually
use a couple of lenses in a tube to
magnify light coming into that tube from outside.
That changed the world view.
It was the first optical telescope that was used to look at the stars in heavens.
It changed our world view.
It showed that the Venus had crescents.
It showed the surface of the moon wasn't perfect, it had ravines and craters.
He saw little satellites around Jupiter and Saturn.
Little miniature solar systems, and
it completely changed the way we look to the universe.
And that only used a very tiny part of the electromagnetic spectrum.
The optical part, which your eyes are sensitive to, is a very tiny part.
If you go further to longer wavelengths,
which means you go into the red part of the spectrum, you go out to the infrared,
you go to the mid-infrared, the far infrared, the millimeter, and the radio.
Like we have radio stations, you have radio astronomy.
And that was developed just after World War II, when the radars that we used
to detect incoming planes and to help us defend against our enemies were turned
to the space instead, and we picked up the first signals from large radio galaxies.
Going the other way, you can go to the ultraviolets, and
then to high energy photons including x-rays.
So, the modern astronomer today doesn't have the blinkered view of
the universe that we had before, which is just what we see through our own eyes.
But they expanded out across the entire electromagnetic spectrum,
from the high energy photons, and the x-ra,y and the gamma ray, and the UV,
right through the optical and beyond to the infrared, to the sub-millimeter,
the millimeter, and the far radio, and everything in between.