Monday 7 November 2011

George Ellery Hale (1868-1938) Hale was the worlds most famous and important "mover and shaker" of large telescopes in the first half of the 20th century. He planned and most importantly raised money for several telescopes that were for a time the largest in the world. A bit of a wacko (he said he had an elf as an advisor) he had a genius for talking to rich folks and convincing them to give money to his projects.

Palomar Hale telescope This telescope was started by Hale, but he died before it was completed. This was the largest optical telescope on Earth from 1948, when it was completed, until 1975, when the Russian 6 meter was built.

Russian 6 meter Completed in 1975, this telescope was the largest until the first Keck 10 meter telescope was completed in 1993. This telescope never quite worked to its potential, due to problems with the site and the sheer mass of the mirror and telescope, which resulted in thermal problems.

(1) The MMT (2) The MMT site In the 1970s, the U. of Arizona and the Smithsonian built the telescope as configured on the left using 6 "Air Force leftover" 72 inch mirrors. The MMT (Multiple mirror telescope) had the light gathering power of a single 4.5 meter mirror. More importantly, it pioneered the techniques for making large telescopes with segmented mirrors. In 1998, the 6 mirrors were replaced with one 6.5 meter spin cast mirrors made by Roger Angel at UA. It is still called the MMT, but that now stands for Monolithic (or Magnum) Mirror Telescope! This telescope is located on Mt Hopkins in Arizona, south of Tucson.

An 8 meter spin cast mirror There are now a number of telescopes with 8 meter class mirrors, or several such mirrors (Gemini North and South, VLT, LBT) and at least one "in progress" with 7 such mirrors (GMT= Giant Magellan Telescope shown on DVD). These mirrors are made by a process called "spin casting" in which glass is melted inside a gigantic rotating oven. The spinning causes the molten glass to take the approximate desired shape of the reflecting surface. This process was perfected by Roger Angel, one of my professors when I was in grad school at U. of Arizona. There is a brief clip of the mirror making process on the DVD segment on the GMT.

Large Binocular Telescope (LBT) This telescope has two 8.4 meter spin cast mirrors on the same mount. This is a project of the U. of Arizona and institutions in Germany and Italy. It is located on Mt. Graham in southeast Arizona. The telescope has been in operation for several years, but due to budget cuts and consequent short staffing the telescope still isn't really working as hoped.

(1) European VLT (Very Large Telescope) (2) One of the 4 VLTs (3) Moonset over the VLT Several views of the VLT. Four identical 8.2 meter telescopes on Cerro Paranal in northern Chile, operated by ESO (European Southern Observatory). A tleast for now, Paranal and Mauna Kea are the two mountaintops with the most optical telescope mirror area. I think Mauna Kea has a slight edge, but am not sure.

********* The largest telescopes of the near term future********

A number of telescopes are either "on the drawing board" or "in progress" that will dwarf those existing today. Not all of these telescopes will actually be built. The status of these projects is constantly changing as institutions jockey for participation and potential funding sources come and go (Where is Hale when we need him?). Two groundbased projects that have a good chance of success are the GMT (Giant Magellan Telescope) and the TMT (Thirty Meter Telescope). These two projects are discussed in the DVD clip I showed.

Artists conception of TMT The TMT will have several hundred "small" segments to make a 30 meter diamter mirror. This project is lead by the U. of California schools and CalTech. There are other partners, including universities in Japan and China. The planned site is Mauna Kea (however, see last slide). This is a $1E9 (1 billion dollar) project. They are still looking for the bulk of the money (Hey, got a spare billion??)

Artists conception of GMT This will have seven 8 meter segments. The equivalent light gathering power is equal to a 21 meter telescope. The project is headed by the Carnegie Institute of Washington, with a number of university partners. Cheif among the universities are: U. of Chicago, Harvard, U. of Arizona and U. of Texas. I think that at least one mirror has actually been made, but I don't know the status of the projects funding.

Emblem of Hawaiian anti-telescope people Not everyone is happy with the thought of a big telescope on their mountain. The TMT will undoubdedly face real political and legal hurdles as they get closer to construction on Mauna Kea.

The LBT on Mt. Graham was delayed many years by political and legal opposition. In the end, it took the Arizona Congressional delegation in Washington passing a special law to allow the LBT to be built!