Video Transcript: Space Telescopes

The first picture in the gallery is really the key to understanding how space telescopes help us.   What this diagram shows is the opacity of our atmosphere.  Now, what that means is how much light does our atmosphere let through at different wavelengths.  So on the vertical axis, you see the opacity from zero to 100%.  So if something is 100% opaque, that means it blocks all light; no light can pass through.  If it's 0%, opaque, it means everything just passes around through; it is totally transparent.

On the horizontal axis, we see the wavelength of light.  So going all the way from .1 nanometers, all the way in the ultraviolet, X-ray, all the way over to radio wavelengths - like 100 meters and beyond.  And what you can see is that our atmosphere is totally opaque in the whole region of the electromagnetic spectrum, all the way up to the just barely ultraviolet part of the spectrum.  Just ultraviolet starts to get a little bit transparent.  

So, if you had X-ray eyes, everywhere you looked you could see X-rays, which is just kind of amazing to imagine - probably give you a headache - but if you had X-ray eyes and you looked up at the sky, it would just be completely black.  You wouldn't be able to see anything.  But if you could somehow get above the atmosphere with your X-ray eyes, you would see bright dots of light all over the sky because there are things in the universe that glow in the X-ray.  Same for ultraviolet and gamma ray, really, you'd see hardly anything.  And it's a good thing because X-rays are harmful to our bodies.

Astronomers might want the atmosphere to wet through X-rays so that they can see into deep space, but the rest of us don't want it because X-rays can give us cancer, gamma rays can give us cancer, and then even the little bit of ultraviolet that's let through, we have to put on sunscreen to try to block it.  So that's blocking a little bit that's let through our atmosphere. 

But you'll notice something awesome which is the atmosphere gets transparent right in the visible part of the spectrum - right where our eyes can see.  We can see not only the sun but the stars because that light passes through our atmosphere.  

And then there's this kind of range here in the infrared where some light gets let through, some gets absorbed, some gets let through some gets absorbed.  That's largely due to water in the Earth's atmosphere that absorbs light on the infrared part of the spectrum.  

And then you have this whole big swath of the far infrared that completely blocks, completely blocks again.  And then you get to the radio part of the spectrum where all that light again is let through.  

So why does this matter?  What matters is if we want to try to completely understand the universe, we need to look at the sky in all the different wavelengths of light from gamma rays all the way through radio.  What that means is that for some parts of the spectrum, particularly gamma, X-ray, ultraviolet, infrared, we really need to have telescopes above the atmosphere.  It's the only way you'd ever be able to see light from space because the atmosphere blocks it.  So that's one of the main reasons that astronomers want to put telescopes up in space.  

But there's a second really important reason and that is our atmosphere is blurry.  So here's a picture that illustrates the exact same nebula taken from a very good ground telescope, like a professional astronomer's telescope on the ground, and then the same nebula taken from the Hubble Space Telescope.  So here's the analogy to consider.

Imagine you're looking at a river and you will be, you see at the bottom of the river there's rocks or maybe there's something shiny there at the bottom of river, but as the water is flowing over the surface of the river, it's blurring that shiny object and you can't really see what it is.  And if you put your head in the water and open your eyes, you may be able to see it better but because there's all that rippling and turbulence on the water, it distorts the image.  The exact same thing happens with our atmosphere because there's a turbulent mass of air above our heads.  As the light passes through it, it gets warped and bent, and messed up.  And so, if we try to capture a picture, our picture gets all messed up in blurry because of the atmosphere.  Now, as you know, astronomers want the sharpest pictures so that they can see as much detail as possible.  That's why they build these huge telescopes.  But the huge telescope doesn't do you very much good if the atmosphere is blurring everything, so by putting the telescope above the atmosphere, you can get a much more crisp picture, because there is no blurring due to that light. moving all over the place.

I want you to notice is that being above the atmosphere doesn't really put us that much closer to the objects in space. Some people think well, yeah, space telescope would be good because you're closer to the stars. But the stars are so far away that that little bit of difference in distance really doesn't matter at all.  It's because you can see more of the spectrum of light and because you're above the blurring effects of the atmosphere.  

Now, we can get these incredibly precise pictures above your assignment sphere, even though our best space telescopes are not that big.  So the Hubble Space Telescope, which is currently the best space telescope we have available in the visible part of the spectrum is not by any stretch the biggest telescope in the world.  It's only about 2.3 meters in diameter. So here you can see the primary mirror of the Hubble Space Telescope. And next to it is this technician standing there, so it's a little bit bigger, a little bit taller than a person.  And you can tell that the Hubble space telescope mirror here is curved because of this person's reflection.  He's like when you look in a mirror at a carnival or even in the mirror that's your spoon.  When it's curved, you get kind of zoomed in, magnified, that's someone standing back here by the person with the camera.  And you can see his face is magnified.  So it's a curved mirror but it's not all that big. When we two meters across.  There are literally hundreds of telescopes across the world that are the same size or bigger than the Hubble Space Telescope.  But none of them can capture as good pictures because Hubble is above the blurring effects of the atmosphere.

Now, here's a picture of the Hubble Space Telescope.  This is the fourth picture in the gallery; the Hubble Space Telescope in orbit.  So this was launched.  Normally, space telescopes are launched on rockets and they're kind of like robots in space.  They just get launched.  No one's there to do anything with them; they automatically run.  And they're controlled by astronomers and scientists back on the ground.  In the case of the Hubble Space Telescope, it was designed to be launched by the space shuttle.  And so it fit within the space shuttle.  Astronauts went up and they released it.  And they designed it this way so that the telescope could continue to be upgraded, so that new cameras could be added, so that repairs could be made.  And so there were several space missions that went up to upgrade and repair the Space Telescope.  The astronauts actually worked on it. Now in order to do that, the telescope has to be relatively close to Earth astronauts, except for when they went to the moon, they really only stay really close to Earth, this space shuttle, it's low Earth orbit really close to earth so.

So Hubble is really close to the Earth and that has some advantages like you can send people to work on it.  But also has some disadvantages like you can only see half the sky at once.   you were to put your space telescope further away, you could actually see almost the entire sky, like every single direction 360 degrees whenever you want because the earth wouldn't be blocking like half your view.  And so many other space telescopes are put even further away from the earth and the next generation of space telescopes that are being planned are put will

way far away from the Earth, even beyond the orbit of the moon.  In fact, the next generation space telescope that's going to be kind of like the replacement of Hubble is called the James Webb Space Telescope and it's been tuned to observe somewhat in the visible part of the spectrum, but more so in the infrared part of the spectrum.  And it's going to be much larger than the Hubble Space Telescope.  It's already being built and it's scheduled to be launched within a few years. 

And this is a comparison of what these two space telescopes look like, Hubble and the James Webb so, on the left, this is the fifth picture in the gallery, on the left side, you see the Hubble space telescope with a person standing next to it for reference.  Again, that's about, you know, six and a half, seven feet in diameter.  On the right hand side, you see a schematic of the James Webb Space Telescope.  And you see that it's way bigger.  In fact, it's six and a half meters, so more like 18 to 20 feet in diameter.  And the way you can build a space telescope that big is by using these what are called segmented mirrors.  So if you look closely at this picture, you'll see that it's not one solid, circular mirror, but it's actually a bunch of hexagons that fit together to make one large curved mirror.  And that bigger mirror can fold up and fit inside of a rocket and be launched way far away from the Earth, and then opened up in space and start making observations.  So amazing telescope, and it's a testament to where we're headed.  Not only putting telescopes in space, but making those telescopes bigger and bigger so we can see smaller and smaller details, so we can see farther and farther into the deepest reaches of space.

All right, that kind of concludes our summary of the tools of modern astronomy.  As we move forward in our class, we're going to start to look at what we've learned from these tools, what we've learned about our solar system about the stars and galaxies, and the universe as a whole. So now we're going to get into the real meat of the science of astronomy. 

All right, we'll see you next time.