The Telescope turns 400 years old this year and in four century period astronomers and telescope makers have been continually making larger and larger telescopes in order to peer deeper and deeper into the mysteries of the universe. There are currently quite a few enormous instruments in use and there are several next generation telescopes being developed that will dwarf anything currently in use. This article takes a look at some of these magnificent monsters of astronomy.
The largest Refractor telescope
Refractor telescopes are renowned for their absolute sharpness of image because they are composed of very large lenses of compounds of glass which gives them crystal clear images. But they are extraordinarily difficult to make in a large size. Their own weight distorts their shape and makes them unusable above a certain size.
The largest refractor in the world is the Yerkes telescope which has a primary lens that is 40 inches in diameter. It was completed in 1897 and was built by the famous master optician Alvan Clark. It represents the pinnacle of refractor telescope making and no larger one has since been built in the hundred years since. Reflectors are much more feasible for larger sizes and there are many of this type that are extraordinarily large. It is with reflectors that we achieve very large instruments.
Here is a list of some of the other largest refractors in the world
- 36″ Lick Telescope at Lick Observatory, Mount Hamilton, California
- 32.5″ Meudon Branch, Paris Observatory, Meudon, France
- 31.5″ Astrophysical Observatory, Potsdam, Germany
- 30″ Pulkowa Observatory, Leningrad
- 30″ Alleghany Observatory, University of Pittsburgh, Pittsburgh, Pennsylvania
- 30″ University of Paris Observatory, Nice, France
- 28″ Royal Observatory, East Sussex, England
- 27″ University of Michigan, Southern Station, Bloemfontein, Union of South Africa
- 27″ University Observatory, Vienna, Austria
- 26.5″ Union Observatory, Johannesburg, Union of South Africa
- 26″ U.S. Naval Observatory, Washington D.C.
- 26″ Leander McCormick Observatory, University of Virginia, Charlottesville, VA.
- 26″ Yale University Observatory, Southern Station, Johannesburg, Union of South Africa
- 26″ Royal Observatory, East Sussex, England
The Largest Reflector Telescopes
Reflector telescopes come in two different types. The first type is the single mirror type where a single piece of glass is cast and polished to make the primary mirror. The second type is the segmented mirror where a series of hexagonal mirrors are assembled together into a single large mirror. This type of mirror looks much like the honeycomb from a beehive and this new technology is allowing telescope makers to make instruments larger than ever imagined.
The largest single piece of glass telescope in the world is the Large Binocular Telescope (LBT) in Arizona. It is a telescope composed of two separate mirrors that are side by side and work in tandem. The light from both of them are blended into one single image. Each mirror is 8.4 meters (330 inches) in width and when used together they create the equivalent of a mirror that is 11.8 meters (464 inches) across which is currently the largest light collecting size on Earth. It is located in Mount Graham International Observatory in Arizona.
Segmented mirrors pose technology challenges that have been overcome in the past decade and now these multiple mirror scopes are being built in extremely large sizes that cannot be rivaled by single piece mirrors. Of the segmented telescopes where a series of honeycomb shapes are assembled together into a single telescope there are three different observatories with these largest of mirrors.
The Image at left shows a segmented mirror. This illustration is of the James Webb Mirror as compared to the Hubble Mirror.
The South African Large Telescope (SALT) is the largest primary mirror scope in the world and it has a segmented mirror that is 11 meters (433 inches) across.
The Gran Telescopio Canarias or GTC is located on the island of LaPalma Spain and it has a segmented primary mirror that is 10.4 meters in diameter (409 inches).
The Keck Telescopes are a pair of telescopes located at the Keck Observatory in Hawaii. Each mirror is ten meters (400 inches) in diameter.
Photo Courtesy of NASA
Bigger Telescopes to come
There are even larger telescopes currently in the proposal, development, or construction stage. Technology improvements over the past decade have made a new scale of telescope possible and this new scale is referred to as ELT or Extremely Large Telescopes and it is the next generation to come. ELT’s are telescopes that are more than twenty meters in diameter which is double the size of existing telescopes. And this doubling of size gives significantly more than double the light gathering power. Most of these scopes will be of the segmented mirror type but one notable exception is the Giant Magellan telescope which will be composed of seven spherical mirrors constructed together so they act as a single mirror. This project is scheduled for completion in 2016. It will be located in Las Companas Observatory, Chile.
The Thirty Meter Telescope (TMT), which is currently in development, will be thirty meters across and composed of segmented mirrors. It is expected to be a telescope of unmatched performance and is predicted to be able to image planets circling other stars. The current time line for this project is for it to be completed somewhere around 2017 – 2018.
What about the Famous Hubble Telescope?
The primary mirror in the Hubble is 2.4 meters across (94.5 inches) which makes it rather small compared to some of the giants listed in this article. So then why is it the most spectacular telescope ever created? The big advantage the Hubble has over all the other telescopes is that it doesn’t have to peer through the soup of Earth’s atmosphere. And this advantage is staggering. That is why the Hubble has brought us some of the most extraordinary images ever recorded.
What comes after the Hubble?
NASA is currently working on its next generation space telescope. It is called the James Webb Space Telescope (JWST). The primary mirror will be 6.5 meters (21.3 feet) in diameter. Launch is planned for 2013.
Since the invention of the first telescope 400 years ago man has been building ever larger telescopes. The telescopes to come will bring us images of planets around other stars and who knows, they may bring us images of the very birth of the universe we live in.