Video Transcript: Cameras

So we've been exploring the tools of astronomy. We've been learning about the light that comes from deep space, we've seen how telescopes can funnel that light down so we can capture it in some way.  But what we haven't seen yet is how do you actually record and store that information that's coming from deep space?  And that's what we're going to look at in this video.  We're going to look at cameras and the important role that they play in modern astronomy.

If you think back to the earliest days of astronomy, before the telescope, and even after the telescope was invented, the only way that people could record information about space was by drawing pictures.  We previously saw drawings that Galileo had made of the moons around Jupiter.  He had to draw their positions night after night.  Now as telescopes got better and better, what we could see with our eyes would improve but we were still limited simply to drawing pictures of what we're seeing in the sky. 

So in this first picture from the gallery, you can see an image of a galaxy.  This is a galaxy M 33, I think, that the astronomer is looking through the telescope and trying to capture in a drawing.  And you can see there's not much detail; it's very fuzzy.  You kind of see some faint sense of maybe a spiral in here, like some arms sticking out, but there's really hardly any detail at all.  And if you wanted to come back maybe a year or ten years later and say, I wonder how different this looks, you're relying on someone else's drawing, or maybe your own drawing.  But how precise was that drawing?  How detailed was it?  Can you count on the fact that oh, this is brighter than it was in my other drawing?  Drawings weren't very reliable.

That's all we had until the late 1800s when photographic film was first invented.  One of the advantages of things in space is that they don't often change very quickly, like over the course of minutes and hours.  And so you can put a piece of film onto a telescope and if you attach a motor to that telescope so that it moves along with the stars as the Earth rotates, then you won't get a picture of star trails.  Instead, you can collect that light through the telescope, have it all fall on the film, and get a very detailed picture of whatever it is you're looking at.  And so this is a great a great way of showing it.  Here's a drawing of this galaxy. But now next, the second picture in the gallery shows a photographic, like a film picture of this same galaxy.  That's amazing contrast to the detail that you can see when you can take a photo with a long exposure. 

Now, why does film help so much?  I mean, film is just the invention of film and using it in  astronomy like revolutionized astronomy.  Why does it help so much?  Well, a couple things. One, film is much more sensitive to light than our eyes are because you can take these long exposures.  Our eyes, in a sense, are like mini video cameras.  They take a picture after picture after picture, and we perceive it all as motion.  But each of those pictures is maybe only like a 30th of a second long. But with a camera, you can leave the shutter open for ten minutes or ten hours, and you can capture way more light. So it's much more sensitive than our eyes possibly can be.

Another reason that photographic film has sort of revolutionized astronomy is because it's the first time that allowed for precise measurements in a couple of different ways.  One is you could precisely measure the location of objects. When it's a drawing, you know, you're like, oh, this is here, and that's roughly there, but with a photograph, you could lay them on top of each other compare from month to month and year to year.  How is this moving?  Where is it located?  How is it changed?  And not just the location, but especially the brightness.  You can measure and observe changes in brightness in objects in space.  And we've already seen how observations of the patterns of motion in the night sky allows us to learn an enormous amount about our planet, our solar system, the moon, but now we have the opportunity to make detailed observations of the patterns and changes that happen in deep space, in other galaxies. And so now we can start to look and try to figure out those patterns and rules and relationships that are happening because we have these measurement tools.  So this process of being able to measure the brightness of objects is really important in astronomy; it's called photometry.  Photo-metry. Photometry.  And photographic film was the first time that we could actually do that.  

Okay.  But that's not the end of the story.  As we all know, we're not taking pictures with photographic film anymore.  In the 1980s, digital cameras first came on the scene.  And some of the very first people to use them were astronomers, because they recognize the scientific value of using a digital camera.  So let me show you the same galaxy now with a digital picture, using what's called a CCD camera.  So this is the exact same galaxy.  And now the amount of detail that you can see is truly staggering.  So let's take a minute try to understand digital cameras because they play a really important role in astronomy.  

So a digital camera or a CCD camera is extremely useful because it's so incredibly efficient and sensitive for light.  So a CCD is a charge-coupled device; charge-coupled device.  And the basic idea is that there's a silicon wafer and when a photon of light, a little packet of light, comes in and hits that wafer, it knocks loose an electron.  And that electron can be stored in an electric circuit, and it can be measured in that circuit.

It is an extremely efficient process; way more efficient than our eyes and way more efficient than photographic film, but it still has all the advantages of photographic film because you can take long exposures, you can measure the exact locations of objects, and you can measure their exact brightness.  So we've come a long way from drawing pictures to these digital cameras.  Let me just show you what these actual CCD things look like.

This picture, the fourth picture in our gallery, is the actual CCD chip, the charge-coupled device, chip.  And you'll see that smooth part in the middle of the box, that smooth surface, that's the silicon wafer where the light hits.  And that silicon wafer is really, in a sense, broken into millions of tiny separate little boxes that are called pixels.  And each one of those boxes is like a separate light bucket.  Each one, when light comes in and hits the top of it, knocks loose an electron and it gets saved inside that bucket.  Then after a picture has been taken and all these little light buckets have their electrons in them, it reads out that information and that's what gets displayed on your computer as a picture.  

A picture is really made up of just millions of pixels.  Maybe you've noticed this.  If you zoom in on a picture until it looks like a bunch of little squares, those are the pixels.  And the brightness in each of those squares, and the color in each of those squares, is really just a number.  It's how much light fell in that particular square.  So, you've probably heard this, your camera is 5 megapixels or 10 megapixels.  That's how many millions of pixels, 5 million pixels or 10 million pixels make up your picture.  So the more megapixels you have, the more little squares and presumably the more information or the more detail that you can capture in your picture.  Now, for astronomers, they want lots of detail, as much detail as they can possibly get.  So they want lots of megapixels and they want really big cameras to put on their really big telescopes.

So here's an example; the last picture in the gallery shows… this isn't the whole camera, this is just the CCD chip. And in fact, there's many chips all working together that was put on a particular space telescope in this case, it's the Kepler Space Telescope.  As you can see, relative to the size of that person standing there, just how big these chips are. This is something like it's over 100 megapixels, this particular camera.

Every single space mission, every single professional astronomical telescope has CCD cameras working on it because they are the most efficient and effective way of capturing light and storing it so that outer space can be measured in great detail.

Alright, that's all I wanted to share with you about cameras.  See you next time.