| The Great Observatories:
Welcome to Hawaii.
At the start of the lecture, I showed you part of a video about the opening of the new Gemini North telescope, located (along with almost a dozen others) on the summit of Mauna Kea, Hawaii. The video made one very important point: these days, observatory sites are chosen because they provide excellent observing conditions, far from city lights, up above much of the atmospheric water vapour, and in a location where the air is extremely steady. Telescopes were not always planned in this way. At one time, as we will see, they were built pretty much anywhere.
Creating an Observatory: Funding a Telescope.It is interesting to consider the evolution in the way big telescopes have been funded over the centuries. There are, roughly speaking, three obvious stages, which I will now describe. Private Funding: There was a time when big telescopes were effectively the private preserve of well-off people who had a particular interest in astronomy. Famous examples include William Herschel (the British astronomer who was the accidental discoverer of Uranus) and the Irish Lord Rosse. Independently, these two built a couple of the world's largest reflectors near their homes so that they could carry out their observations (although for Rosse it was more a hobby than a profession). Even today, amateurs with home-built telescopes can contribute significantly to observational endeavours like: the search for comets; programs in which astronomers monitor the variability of bright stars; and searches for novae and supernovae (exploding stars). One justly famous example is David Levy, a Queen's M.A. graduate, who is the co-discoverer of Comet Shoemaker-Levy, a comet which crashed spectacularly into Jupiter in the summer of 1994. Typically, such astronomers do not use very large telescopes. Private Endowment: In this stage, which lasted (roughly speaking) from the late 1800's to the middle of the 1900's, rich benefactors donated the money to establish observatories although they themselves were not practising astronomers. I gave some examples and anecdotal histories in class. For instance: (i) James Lick made his fortune by funding "gold rush" hopefuls in San Francisco. He provided them a grubstake by buying up their land cheaply, and wound up owning most of what is now downtown San Francisco. He wanted to build an enormous pyramid in the city to commemorate himself, but was persuaded by the Regents of the University of California to build an observatory instead: Lick Observatory, just east of San Jose. (ii) A man named Yerkes made his fortune building street car systems, and donated the money for the Yerkes 40-inch refractor, still the largest such telescope in the world. It is at Williams Bay, north of Chicago, and is operated by the University of Chicago. Yerkes was apparently quite an unscrupulous businessmen, by all accounts, and was never favoured with the respect which he hoped his endowment might buy for him. (iii) David Dunlap made his fortune in Ontario silver mines, and was interested in astronomy. After his death, his widow donated a lot of money to the University of Toronto, who built the David Dunlap Observatory in Richmond Hill. When it opened in 1935, it was the second-largest telescope in the world. (iv) The Carnegie Foundation, established by the Scotsman Andrew Carnegie , funds many philanthropic endeavours, including public libraries. It provided the money for the famous 200-inch telescope on Mount Palomar, which saw first light in 1950. Amazingly, the days of such generosity are not completely gone: the new Keck telescopes on Mauna Kea are being provided by a Mr. Keck, the head of Standard Oil (I believe). The total cost is in the region of 200 million dollars; the telescopes are operated by the University of California. Multi-National Collaboration: Keck Observatory notwithstanding, the "standard model" nowadays is for several nations to pool their resources in the establishment of big observatories. The reasons are fairly obvious: What might be too expensive for one nation, especially a little one, can be made affordable if it is shared. There is no real need for every nation to have a huge telescope, given the finite numbers of astronomers around. Not every nation has an observing site of great quality. Canada does much better to have a share of a facility in Hawaii than to have our own telescope, however big, anywhere in Canada. There are many multi-national facilites. To name a few: the Anglo-Australian Observatory (where I worked before coming to Queen's), shared by the U.K. and Australia the Canada-France-Hawaii Telescope, on Mauna Kea the Cerro Tololo Inter-American Observatory , in Chile (shared with the U.S.) the La Palma Observatory in the Canary Islands, shared by the U.K., Denmark, and Spain the European Southern Observatory, at La Silla in Chile, owned by a host of European countries the Gemini 8-metreTelescopes (one in Hawaii, one in Chile) in which Canada has about a fifteen percent share, along with the U.K., the U.S., Chile, Brazil, Argentina and Australia.
Is it Worth All the Money?This is a question we should think about seriously. Before attempting to answer it, you might like to look back at my introductory lecture, one in which I discussed some of the reasons for doing astronomy at all. Although I gave some practical reasons there, I should perhaps remind you that there don't have to be practical reasons for all activities. For instance, you might ask why we should ever bother to put on another production of `Hamlet'? Why not just videotape a very good production today, and make the tape available to anyone who wants to see it? Why write any more symphonies or songs? Why play any baseball games? Of course, it can be argued that these endeavours really have an indirect practical benefit which is not immediately obvious. Perhaps they provide a happier social setting and thus a more peaceful and constructive community, for instance. But the same may be true of astronomy and other learned activities. It is, in any event, important to keep things in perspective. The simple fact is that not much money is spent on astronomical research, despite the apparently intimidating cost of the telescopes and so forth. Consider the Canada-France-Hawaii Telescope, for instance. It was built at a cost to Canada of about twenty million dollars (with an equivalent amount coming from the French). Such a facility has a fairly long scientific lifespan -- in fact, it has been in operation for just over twenty years and is still very productive. We have to think of the initial capital costs as being effectively spread over all those years, but then not forget to add in the ongoing operating costs (since the Observatory employs engineers, administrators, secretaries, computer personnel, and so on). The continuing operating costs to Canada are about 2.5 million dollars a year - about a dime per year for every Canadian citizen! - while the amortized capital costs are probably about the same again, certainly not more. In short, for less than twenty cents per person per year , Canada has enjoyed the world's best telescope (as it has been for the last decade, although newer telescopes are now overtaking it) and has produced astronomical science unmatched by facilities elsewhere. The amazing thing is not how much it costs but how little! It is undeniably true that we should always attempt to spend public dollars in beneficial and sensible ways: improved social programs, research into disease, and so on. But the really wasteful spending in the western world has, for some decades, been into things like armaments -- although less so in Canada than in the United States. The total amount of money that we, as a nation, put into pure scientific research is in fact very small. Canada's entire annual share of the CFHT is very much less than the payroll of the Toronto Blue Jays, for instance - indeed it is less than the salary a single `marquee player' receives. Consider an even more expensive enterprise. The Hubble Space Telescope, perhaps the best-known icon of modern astronomy, took more than fifteen years to develop, build, and launch, at a cost of 2 billion dollars. That sounds like a great deal, but consider: there are 250 million Americans (a quarter of a billion), so the cost to each of them was about 8 dollars, spread over fifteen years or more. Thus the net cost per person is about fifty cents a year , about as much as a single cup of (cheap) coffee a year. And for this paltry sum we learn about the very origins and nature of our universe!
Where to Put a Telescope.As noted earlier, telescopes were once built wherever it was convenient. Lord Rosse and William Herschel put theirs in their gardens, for instance, so that they were just a short stroll away. The Lick Observatory was put on Mount Hamilton, outside San Jose, because James Lick could see it from his home. The Dunlap Observatory was placed in Richmond Hill because it was easily accessible, by street car, from the University of Toronto. (One original plan was to have it at the corner of Bathhurst and St. Clair in what is now downtown Toronto.) Things have changed. Modern telescopes are expensive, and no effort is spared in finding the most productive and reliable sites for them: we need to justify the expenditure to a critical public. Here are the factors which have to be considered: Political stability: is there likely to be a civil war? Is the regime politically distasteful? The British government, for instance, stopped funding the South African Astrophysical Observatory many years ago as an anti-apartheid statement. Ease of access: Are there roads, and nearby communities from which we can hire service personnel and within which employees can live? Is water available? If it is virtually impossible to get to the site, and inhospitable once there, the other qualities - dark sky, stable weather, etc. - may not matter. The quality of the site. This is of course the pre-eminent consideration. Included in this catch-all topic are a variety of important factors, including: The "seeing": how turbulent or blurry is the atmosphere? (The word ``seeing'', by the way, has a real quantifiable meaning and technical definition for an astronomer: it is not just a vague buzz-word.) The weather: are the skies typically clear, or cloudy? The transparency of the sky: if you are at high altitude, for instance, there is less air and water vapour above you, and more light (especially infrared radiation) can get through The darkness of the sky: In class, I showed you a night-time satellite image of North America. The bright lights near Toronto (the David Dunlap Observatory), Chicago (Yerkes Observatory), San Francisco (Lick Observatory), Los Angeles (Mount Wilson Observatory) and San Diego (Palomar) were all too obvious! Tucson, in Arizona, is quite dark and is the home of a major observatory called Kitt Peak. In fact, Tucson has local ordinances which prohibit excessive 'light pollution.' In addition to all of these considerations is the obvious requirement that there be observatories in the southern and the northern hemispheres so that there can be complete sky coverage. A telescope at the North Pole, for instance, would only ever see half the sky. A telescope on the equator could see the whole sky, but stars near the poles would always be awkwardly placed very near the horizon. The best solution seems to be to have some telescopes at middling latitudes north and south of the equator (say, in Chile and Hawaii).
Observing at Mauna Kea.In class, I took a few minutes to describe to you the sort of observing project which takes me to Mauna Kea to use the CFHT. Since my research concerns the nature of remote galaxies, it is premature to describe the science too deeply now; but I wanted to take the opportunity to tell you a little about what it is like to be on the mountain and work there. The first thing I can tell you is that it is very exciting, especially if you are an astronomer. It is a great privilege to be allowed unimpeded use of one of these sophisticated and powerful facilities to do whatever research you find provocative, and just being on the mountain, the home of so many great telescopes, is quite a sensation. You meet and talk with some of the world's great astronomers and scientists (and they with you!) because they are there to use other telescopes, or even your own telescope after your scheduled run is finished. So there is a real spirit of scientific adventure on the mountain and in the various offices. But the actual observing is very different from what you may imagine, thanks mostly to the demands of the site itself. On arrival in Hawaii you instantly travel to Hale Pohaku, the lodge at the mid-level site (at an altitude of about 9000 feet) to live for the duration of the observing run. This is very important. Working at high altitude can be difficult, and if you develop sicknesses like high-altitude pulmonary edema (HAPE) or cerebral edema (HACE), it can be very serious, or even life-threatening. That is why, if the conditions turn foul, you have be prepared to evacuate the summit rapidly. The problem is not so much simply getting sick as getting sick while unable to leave, in which case the high altitude sickness becomes a real concern. I am not joking when I talk about foul weather on the summit. `Mauna Kea' is Hawaiian for `White Mountain', a name which arises because of the frequent heavy snows on the summit. At altitude, the temperature is never more than a few degrees above or below zero Celsius, and there can be enormous blizzards which can deposit feet of snow in very short order. The winds can be ferocious -- I have experienced winds of more than one hundred and fifty miles per hour there -- and freezing rain is not uncommon, usually in strong winds. Since the roads are quite precipitous, this can add to the danger. In addition to this, of course, one is working nights -- typically very long nights. It is not uncommon to drive up to the summit from Hale Pohaku at about 2 P.M., to spend the afternoon hours setting up and calibrating the electronic instruments, to observe all night (from perhaps 8:00 P.M. to 6:00 A.M.), to use the morning twilight hours to recheck the instrumental calibration, and then to drive down to Hale Pohaku for about five or six hours of sleep before lunch and a return to the summit. All in all, observing runs can be exhausting, frustrating, and just plain infuriating, especially when you spend precious money from your research grant to take yourself and a graduate student all the way out there, only to lose the entire run to high winds or an instrumental catastrophe. As vexing as that is for me, it is worse for the student, of course! His or her whole thesis may depend on the hoped-for data. And the problem is that there is no guarantee that you will get any more telescope time. Every grant of time is won in a competition with other scientists who want to use the telescope for other purposes. A typical big telescope is oversubscribed by about a factor of three or four, so there is a real element of lottery in the enterprise. But when the conditions are ideal, and the instrument works well, there is nothing like it!
A Prosaic Question: Why Glass Mirrors?As we have seen, reflecting telescopes work because the light bounces off a shiny surface and is brought to a focus by the carefully-designed shape of that surface. But why do we use glass at all? Why not make big mirrors of wood, or steel, and merely coat them with a shiny surface? As it happens, this is essentially what was done for centuries after Newton. People like William Herschel and Lord Rosse built large reflectors in which the mirrors were made of a special metal alloy called speculum, which was simply burnished or polished to make it very reflective. It is only in the last century or so that the use of glass has become standard, and here are some reasons why: Ease of production: glass can be readily melted at a moderate temperature, and once molten can be poured into a mould of approximately the desired shape. Thereafter, it is fairly soft and easy to grind and polish to the precise shape wanted. Cheapness: it is relatively inexpensive. Lightness: glass is fairly light, so a big slab of it does not weigh as much as many other materials would. This reduces the mechanical load on the telescope structure. Thermal properties: As I noted in an earlier section, there are modern kinds of glass that have almost zero "coefficient of thermal expansion." What this means is that the glass neither expands nor contracts as the temperature changes; thus the mirror does not change in shape, and the image quality is maintained. (Steel, by contrast, expands a lot when it is heated. That is why railway tracks have gaps in them, so the rails can expand rather than buckle when they get heated on a summer's day.) Of these properties, it is the last -- the thermal property -- that is the most important. There are different kinds of modern glass, some of them quite expensive, which are used in telescope construction. Many of the older telescopes, however, do not have this kind of glass. Consequently, it is very important for them in particular, but for all telescopes in general, that we try to provide a stable temperature in the dome. Our aim is usually to keep the dome as cool in the day as we expect it to be at night, so that when we start observing there are no big temperature differences. One of the ways this is accomplished at the CFHT is by active refrigeration of the dome: there are actually big cooling coils embedded in the cement floor.
Making the Glass Shiny.Merely making a mirror out of glass is not enough, of course, because a slab of pure glass is not very reflective. The mirror has to have a coating applied to it. It is put into a big "aluminizing tank" out of which all the air is pumped; then small bits of aluminum are vaporized by strong electric currents so that the whole inside of the vacuum tank, including the mirror, is coated with a thin (millionth-of-an-inch) layer of shiny aluminum. This operation has to be repeated from time to time, typically once a year at the big observatories, because the mirror gets dusty and dirty. The mirror has to be removed, washed, dried, and re-coated in an operation that takes a couple of days. This discussion may strike you as uninteresting, but there is a provocative way to think about it. The entire structure of the telescope, with a mass of several hundred tons, is expressly designed to hold this thin layer of shiny aluminum in exactly the right position and configuration to reflect the incoming photons onto a detector. In a sense, this is the most important and critical part of the telescope - a layer of aluminum which weighs less than a Coke can! Previous chapter:Next chapter
0: Physics 015: The Course Notes, Fall 2004 1: Opening Remarks: Setting the Scene. 2: The Science of Astronomy: 3: The Importance of Scale: A First Conservation Law. 4: The Dominance of Gravity. 5: Looking Up: 6: The Seasons: 7: The Spin of the Earth: Another Conservation Law. 8: The Earth: Shape, Size, and State of Rotation. 9: The Moon: Shape, Size, Nature. 10: The Relative Distances and Sizes of the Sun and Moon: 11: Further Considerations: Planets and Stars. 12: The Moving Earth: 13: Stellar Parallax: The Astronomical Chicken 14: Greek Cosmology: 15: Stonehenge: 16: The Pyramids: 17: Copernicus Suggests a Heliocentric Cosmology: 18: Tycho Brahe, the Master Observer: 19: Kepler the Mystic. 20: Galileo Provides the Proof: 21: Light: Introductory Remarks. 22: Light as a Wave: 23: Light as Particles. 24: Full Spectrum of Light: 25: Interpreting the Emitted Light: 26: Kirchhoff's Laws and Stellar Spectra. 27: Understanding Kirchhoff's Laws. 28: The Doppler Effect: 29: Astronomical Telescopes: 30: The Great Observatories: 31: Making the Most of Optical Astronomy: 32: Adaptive Optics: Beating the Sky. 33: Radio Astronomy: 34: Observing at Other Wavelengths: 35: Isaac Newton's Physics: 36: Newtonian Gravity Explains It All: 37: Weight: 38: The Success of Newtonian Gravity: 39: The Ultimate Failure of Newtonian Gravity: 40: Tsunamis and Tides: 41: The Organization of the Solar System: 42: Solar System Formation: 43: The Age of the Solar System: 44: Planetary Structure: The Earth. 45: Solar System Leftovers: 46: The Vulnerability of the Earth: 47: Venus: 48: Mars: 49: The Search for Martian Life: 50: Physics 015 - Parallel Readings.
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(Tuesday, 20 October, 2020.)