The Billion-Dollar Telescope Race

One of the reasons that there wasn't much in the way of development of larger telescopes in the late 1970s and 1980s was the development of the CCD. Prior to the CCD, astronomers used photographic plates to take their images, and photographic plates have horrendous efficiencies. A typical photographic plate will only register a few percent of the incident photons. A CCD, however, has an efficiency very close to 100% (except at really low wavelengths). Almost immediately after its invention, new instruments with CCDs were built to be put on existing telescopes. [1] Because the efficiency was a factor of ~30 larger, it was as though you had quintupled the diameter of your telescope. There wasn't much of a reason, then, to invest in huge new telescopes when you could effectively have a huge new telescope just by building a CCD detector.

Also, as a graduate student at Ohio State I would be remiss if I neglected to mention that the Large Binocular Telescope was originally planned to be built at the same time as Keck. It was originally conceived to be larger and with OSU providing a large fraction of the funding. OSU's president, Gordon Gee, cut funding for the project in the early 90's, however, which threw the project into disarray. Most of the faculty in the Ohio State astronomy department resigned in protest which is why Ohio State has had a department with relatively young faculty. Due to problems funding the project and technical difficulties (putting two very large mirrors on a common mount turned out to be harder than anticipated), the telescope had to be scaled back and it only saw first light in 2005.

[1] As an aside, astronomy has been one of the major drivers of improvements in CCD technology. CCDs in consumer devices are generally used in photon-rich environments and the users can tolerate a lot of noise in their images. Astronomers, however, demand very low noise and use their CCDs in photon-poor environments, and the production of these kinds of devices has required major improvements in CCD technology.

You can check out the following SVG to see a comparison of telescope sizes:

http://upload.wikimedia.org/wikipedia/commons/c/c5/Compariso...

Several years ago I backpacking in the Atacama desert in Chile. That's where a lot of telescopes are built because it's so dry. I stopped in one city and I tried to find an observatory through my hostel that took visitors but had no luck. Guess whatever tour was available wasn't popular enough. Has anyone had any luck in Chile?

That's pretty impressive. Given the size and importance of the mirrors, I wondered how they actually clean them. Came across this: https://www.youtube.com/watch?v=CkV8RRRu7gE

Will any of these new scopes be able to image exoplanets?

The GMT telescope has mirrors 8.4 meters across with a fault tolerance of 19 nanometers. If you were to scale that mirror up to the size of Earth, the biggest imperfection would be just 2.8 centimetres high. That is amazing.

Does the mirror have to be round?

Can you make an extremely long, but not very tall mirror? Seems like that would be easier to build.

Disappointed the article didn't discuss the pros/cons of earth-based telescopes versus space based. Why build earth based telescopes when you have the atmosphere in the way?