 Greetings and welcome to the Introduction to Astronomy. In this lecture we are going to talk about space telescopes or telescopes that are put out in space. And astronomers do this for good reason. Some things simply cannot be seen from the surface of the Earth. So visible light makes it down to the surface of the Earth, as do radio waves, but when we look at other types of electromagnetic radiation, we cannot see them. And in fact only a very small portion of the electromagnetic spectrum is able to get through the atmosphere. So here we see, for example, visible light makes it through. Lots of radio waves make it through. But if we want to look at things like gamma rays and x-rays and ultraviolet in the short wavelength portion, very little of that gets through the atmosphere. A lot of infrared and even shorter wavelength radio are blocked out as well. So if we want to observe these, we have to get up higher than the atmosphere, high above the atmosphere, in order to be able to see them. So why do we want to put telescopes in space? Well, we want to see those other portions of the electromagnetic spectrum. And here we look at the Crab Nebula, which is an example of a supernova remnant. And we can see it in the visible light. We can see that from Earth, and that was our only view from up to about 100 years ago. Going back about 50 or 60 years, we could add in the radio part of the spectrum. But we couldn't see it across the entire spectrum. Now that we have telescopes out in space, we're able to get good infrared images and ultraviolet and x-ray and gamma ray. And if you look at them, you can see that there are some similarities. But there are also some distinctive differences as to the different parts of the nebula that are visible in each type of wavelength. So getting a complete picture means we need to look at an object across the entire electromagnetic spectrum. So let's look first at some infrared observatories. Infrared is one of the easier ones because all we have to do is get above the water vapor in the lowest layer of the atmosphere or the troposphere. Once we are up above water vapor, most of the infrared does make it down to the Earth. It is water vapor and other gases like that that absorb the infrared radiation. So we've used things like balloons and the Sophia aircraft shown here that are possible to be able to observe even assisted very high altitudes. You can fly very high in the sky here and have your infrared telescope looking out at the sky and you can actually get observations that way. All you need to do for infrared is get above the water vapor in the atmosphere. In fact, there are some infrared telescopes on high mountain tops that can also be used. Now even better though, you can get out into space. So we can put telescopes out into space and look at what those are. We can have a satellite like this one out in space and that can observe infrared as well. And of course it has the advantage that it is up above the atmosphere so there is absolutely no water vapor to have to worry about. The difficulty with these is that the infrared detector needs to be cooled. It has to be very cold. Otherwise, if you remember black body radiation, something that is room temperature for example is giving off infrared radiation. We give off infrared radiation all the time. But it's not only us, also any tables and chairs and other objects are also giving off infrared radiation. So if the detector is warm enough or at a certain temperature that it is giving off infrared radiation as well, so it's essentially could be glowing in the light that it is trying to detect. And you can imagine your CCD glowing in visible light you would not be able to see anything because you'd be overwhelmed by that light. So the same thing here, if your infrared object is not cooled using things like liquid nitrogen to bring it down to really cold temperatures so that it does not emit much infrared and that is one of the big problems with infrared observatories that things like radio telescopes or optical telescopes generally do not have to worry about. Mirrors are not giving off visible light for example and CCDs do not give off visible light so they do not have to worry about this kind of interference. So that is one thing that you have to do with an infrared telescope. Now one of the most famous space telescopes is the Hubble Space Telescope which was launched in 1990 and has a 2.4 meter mirror so very small mirror by comparison to many of the other optical telescopes here on earth. The key is that it is above the atmosphere of the earth so we get no atmospheric interference and that means that we can observe exactly what the higher resolution images with no atmospheric blurring because of the twinkling of the stars. It also can observe infrared and ultraviolet so it's not constrained to just observe visible light a regular mirror will also reflect infrared and ultraviolet light and that allows us to be able to study a wider range or wider range of the electromagnetic spectrum not completely but at least a portion of the infrared and ultraviolet can be visible with the Hubble Space Telescope. Now when the Hubble Space Telescope was first launched the images were not as beautiful as they expected and it turns out that there was an issue with the mirror that was ground to the wrong shape. It was just slightly off but it was enough to completely blur the images. Fortunately a space shuttle mission a year or two later was able to go up and fit a corrector over it to adapt. Once we knew exactly what the issue was and what shape it was ground to we could then give it essentially a pair of glasses to correct for that error and it has been operating for decades now giving us some of the best views of the universe ever. Now that Hubble primarily looks at visible light we can also look at higher energy observatories and those are things that look at ultraviolet x-rays and gamma rays pretty much for these you've got to get above the atmosphere to be able to see them. So some examples would be the International Ultraviolet Explorer or IUE which was up for several decades constantly scanning and looking and studying objects in the ultraviolet portion of the spectrum. We have the Chandra X-ray Observatory and the Fermi Gamma-ray Observatory which have both been, Chandra's been up for almost two decades and Fermi for a decade now. So being able to study different parts of the universe. So not only is Hubble Space Telescope in orbit but we have other telescopes in orbit as well to help us to observe things like infrared, ultraviolet, x-ray, and gamma-ray. And as I've mentioned that gives us that complete picture of an object. If we can study it with all of these different wavelengths study all of it at once and then put all of that together we're really getting a complete picture of the object and not just one little segment of it which was all we could do for most of the history of astronomy was look at things in the visible portion of the spectrum. Now we're able to look at it at all different ones of these. Now what might the future hold? Well currently scheduled for launch in the fall of 2021 is the James Webb Space Telescope. And in a way this will be the successor to the Hubble Space Telescope. And again that will be launched in the fall of 2021 and will be a much larger telescope containing a 6.5 meter mirror as compared to the 2.4 meter mirror that Hubble had. So not quite a little more than about two and a half times larger than the Hubble Space Telescope's mirror. And it's also a different design as you can see in the image here. It will actually have a honeycomb structure which allows smaller pieces to be put together to build a much larger mirror. Now we've done that with mirrors here on the earth it's a lot easier to build many small mirrors and put them together than it is to build one gigantic mirror. So many large mirrors are actually built this way. It also allows the structure to be able to fold in into a much more compact configuration for launch. So when this is launched it will not look like this. The mirror will actually be folded down and compacted and will not actually expand out into this configuration until it reaches its proper orbit. And at that point it will extend out as seen and will give a chance to be able to begin looking at the sky. Now what we're going to look at with this is a little bit different than Hubble which looked at visible ultraviolet and infrared. The James Webb Space Telescope is a long wavelength telescope and will look primarily at infrared light but will also see red and orange parts of the visible spectrum. So the shorter wavelengths the blues and the greens will not be it will not be sensitive to but it will be able to see these much longer wavelengths. Its orbit will also be a little bit different than Hubble. Hubble was designed with the space shuttle in mind. Its mirror was constrained by the size of the space shuttle bay that would launch it. And the orbit was in a low earth orbit that could then be serviced by the space shuttle. The James Webb Space Telescope is going to be out beyond the moon for its orbit so it will not be in a low orbit. It will be well out beyond the moon in what we call a Lagrangian point which is a stable area in the local gravitational system. And hopefully in fall of 2021 we will be able to get our first images from James Webb. What should be able to be significantly better than the amazing images we've gotten from Hubble over the last few decades. So we look forward to that. Hopefully we'll remain on schedule. It's been delayed a couple of times. But hopefully by fall of 2021 we will begin looking for that launch. So let's finish up with our summary and talk about what we've covered in the lecture this time. So what we have is on earth we can only use visible light and radio waves. Those are the only ones that completely penetrate the earth's atmosphere and can be observed from the surface of the earth. Space telescopes can be used to give us a new view on the universe. And also they do not have to look through the earth's atmosphere. So not only do they not have the issues with the earth's atmosphere blocking out their light completely but they don't have the blurring effect of earth's atmosphere. There are a number of space telescopes that we talked about and future ones are planned to continue making observations from space. So even though it is more expensive to put a telescope in space than it is to have one here on earth it gives us completely different views of the universe. And that makes it very much worth the additional expenses. So that concludes our lecture here on space telescopes. We'll be back again next time for another topic in astronomy. So until then, have a great day everyone and I will see you in class.