Space astronomy is an important, but also expensive and complex part of the astronomy enterprise. As you recall, most of the electromagnetic waves that run from Gamma rays to radio waves, do not penetrate the Earth's atmosphere. The only way we can observe these waves from celestial sources is in Earth orbit or even beyond. So space astronomy is an essential part of how we learn about the universe. The most iconic space observatories, are NASA's missions called the Great Observatories, which includes a Compton Gamma-Ray Observatory, now defunct, and three currently operating missions; the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra Observatory, working at x-ray wavelengths. These are NASA centerpieces for space astronomy. Each of them having caused multiple billion dollars, space astronomy doesn't come cheap. Square meter for square meter, it cost 10 or 20 times more to put a telescope in orbit than it does to operate that same telescope from the ground. So you have to have a good reason to go into space. The strongest reason of all, of course, is the fact that you cannot detect those waves from the ground. But you also need an astronomical reason to be interested in those invisible wavelengths. These missions are not only expensive, but they're difficult to get approved. If we look at NASA's manifest over the last decade, we'll see that the missions that has planned, due to limited budgets, have often been delayed at close to a year per year. So missions that astronomers dreamed of 10 or 20 years ago, are only just coming to fruition. Space astronomy is a long game. The people involved in it have to have the patients to deliver almost their whole career towards one telescope getting launched. The ultimate place for a space observatory would actually be the far side of the moon. It's incredibly dark, it's shielded from all artificial sources of light, and it's also shielded from sunlight, and its geologically quiet. There's almost no radio interference or light contamination of any kind, the perfect place for an optical or radio observatory. The far side of the moon is a place where we could operate a robotic telescope using technologies that we've tested at ground-based observatories, and it wouldn't be much more expensive than conducting moon landings for other purposes. So astronomers still have a hankering and they have well-developed plans for an observatory on the moon. At the moment, it's unfunded. NASA's Great Observatories, three out of four which are operating right now. Mean, this is a wonderful time for space astronomy. One of those three observatories; the Spitzer Space Telescope, ran out of its primary cryogen a year or so ago, but is continuing in what is called warm mode and still doing exceptional science at infrared wavelengths. The other two facilities; Hubble Space Telescope and the Chandra X-ray Observatory, are doing frontier science in all fields from comets to cosmology, and are producing discoveries virtually weekly. These flagship missions are billion dollar plus missions, but NASA and other space agencies also have a portfolio that includes mid-scale missions, things that might cost a few hundred million dollars. Which sounds expensive, but for space astronomy is actually quite cheap. These missions are different in concept. The Great Observatories are like Swiss army knives with a complex suite of 8-12 instruments, and they're able to do everything, and they need to do everything well. These mid-scale missions are different in concept. They're designed to address one scientific issue, with one instrument typically, and do it with exceptional precision. Excellent examples of these instruments which you'll hear about later in the course, are WMAP which looks at the microwave background from the Big Bang, and Kepler which is designed to find Earth-like planets. Both missions have succeeded exceptionally well for a price tag under half a billion dollars. Finally, there are flagship missions still under concept and not yet funded that are really out of the box because they go beyond the detection of normal electromagnetic radiation. A good example of these is LISA, the Laser Interferometer Space Antenna, which is an interferometer that we've already talked about in space designed to detect gravity waves. This is a frontier instrument that will do something that no ground-based telescope can do. Astronomer's dream of being able to detect gravity waves from space using this instrument, but it's at least a decade off. Currently, there are over a dozen space-based observatories some, doing specialized missions and some the great observatories doing a little bit of everything. It's actually a wonderful time for space astronomy, the engineering and the techniques involved are state of the art. Many of these missions cannot be serviced or fixed if anything is wrong when they're launched, everything has to be made just right on the ground. Most astronomers consider the scientific payoff to be worth the high price tag. That's the big and expensive end of the scale of astronomy. What about the other end accessible to all of us? In 2009, it was the 400th anniversary of Galileo's first use of the telescope to study the night sky. In commemoration of that event, very important for most astronomers, the Galileoscope was produced. The Galileoscope is a modern version of Galileo's best telescope using modern optical components, it's entirely made out of plastic in fact. This has found its way into the hands of hundreds of thousands of people, and has provided the best entree to the night sky for the average person. It's still a highly recommended way of learning about the sky, but it's always a good idea to spend an extra $15 on a tripod. Galileo's telescope has a very small field of view and is a long device, so holding it steady on the sky is difficult. A tripod makes that much easier. If we're going to summarize the history of optical telescopes over 400 years in one graph, it would be the improvement in sensitivity over the eye in factors of 10. Galileo's improvement with his best telescope was a factor of a hundred. Then through the 17th, 18th, and 19th, century larger and larger mirrors were produced to increase that to factors of millions. With the development of electronic detectors and sensitive telescopes in space, the fullness of four centuries of telescopic design is a factor of 10 billion times fainter than the eye can see. That's the limit of the Hubble space telescope when it stares at one region of the sky for a week. The improvement in resolving power is not the same enormous factor relative to Galileo's telescope or the naked eye, but it's still several orders of magnitude, and with interferometry several orders of magnitude more. So 400 years of telescope has given us enormous differences in light grasp and sensitivity and resolution. Space astronomy is an important way to learn about the universe. The missions are expensive, but they do things that cannot be done from the ground. Often looking at invisible waves that are extinguished by the Earth's atmosphere. Astronomers currently have a portfolio ranging from Great Observatories that cost multi billions of dollars to specialist missions doing particular scientific experiments. All are important, and together, they've delivered a factor of 10 billion gain in depth over the night sky observed by the naked eye.
