What's the World's Biggest Telescope?
In astronomy, bigger is better. So what's the very biggest telescope of them all?
The Canary Islands off the coast of Morocco house the largest glass mirror reflector telescope in the world. The Gran Telescopio Canarias (GTC) is owned and operated primarily by Spain. The surface of its concave focusing mirror eschews the parabolic glass bowl design of traditional telescopes. The reflector is actually 36 small hexagonal German glass mirrors tiled together in the shape of a single large hexagon with a missing tile in the center. This design is very similar to the slightly smaller Keck telescopes in Hawaii. GTC also employs adaptive optics to constantly fix the distortion of incoming starlight caused by its passage through atmospheric turbulence. Larger glass telescopes have been proposed, but none will be open for at least several more years.
It's worth noting that the famous Keck observatory in Hawaii also has a claim to the "biggest" title. Their two telescopes actually measure more light in total than GTC and can be used in parallel like a set of binoculars to further improve performance.
Light is just one type of wave. Radio waves are electromagnetic radiation with a much much longer wavelength. Radio telescopes look like giant satellite dishes. New Mexico houses an array (creatively named Very Large Array) consisting of 27 dishes each 82 feet in diameter. This iconically beautiful telescope is used for looking at all sorts of radio-emitting astronomical objects (black holes, quasars, supernova remnants and many others) and as well as searching for E.T.
However, VLA is blown out of the water by the size of the largest single radio telescope: the Arecibo radio telescope in Puerto Rico. This dish, made famous in the James Bond film GoldenEye, is suspended above a valley between hilltops. It is 1000 feet across and has a surface area of more than 25 acres. This behemoth has been used to take radar images of asteroids, measure pulsars and time the rotation of planets.
There's a still larger telescope, used for finding invisible particles from space. The Icecube neutrino observatory detector can't be seen from above, but the control room can. The detector itself is enormous: a cubic kilometer of ice. The enormous size of this detector is necessitated by how hard neutrinos are to see: a single neutrino is as likely to pass right through a piece of lead a light year thick as it is to hit any lead. While (very) roughly 10^20 neutrinos hit the system each day, only a handful are detected.
The telescope is really looking for the highest energy neutrinos. It sees interesting neutrinos about 10 times per year, and a very unusual one roughly once annually. Unlike most neutrinos which are created by the sun and the cosmic microwave background radiation, these high energy particles likely originate from far beyond the galaxy. Icecube has the largest volume of any telescope on earth, but its largest dimensions, scale, and expense are only second biggest.
The biggest telescope of all is right here in the US, and you probably haven't heard of it: LIGO, the Laser Interferometer Gravitational Wave Observatory. It looks for gravity waves instead of light waves. LIGO does not collect and focus radiation. It shoots laser light roughly 186 miles and measures whether that light has traveled more or less distance than it should have. A miniscule discrepancy in distance traveled would indicate the passage of a gravitational wave, ever-so-slightly expanding or contracting spacetime along the 186 miles of travel.
Two LIGO 'arms', positioned in an 'L', can be seen by satellite. There are four arms altogether, located at two separate facilities: one in Livingston Louisiana and one in Hanford Washington. Each main arm is 2.5 miles (4 km) long!
Gravity waves may be created by far distant events such as black holes merging. As the wave travels millions of light years and passes through the earth and LIGO, spacetime along one arm or the other of the telescope will shrink or grow by that millionth-of-an-atom's width. The light in the other arm will be unaffected. When the light waves from each arm are collided together, they will interfere. Two waves that have traveled precisely the same distance will interfere without canceling any of their brightness. Waves that have travelled slightly more or less due to spacetime disturbance along their path will interfere destructively: their combined light will be a tiny fraction less bright.
LIGO is the largest and most expensive project ever completed with only NSF funding. It has not yet detected a gravity wave. Given how well Einstein's General Relativity theory has held up in all experimental tests, smart money is that they will detect one eventually.
Astronomers can't create events; they can only watch them. The larger and wider their eyes, the more they can see. Ever-larger telescopes strive to capture more and more of the limited light that we receive to help us reconstruct the universe around us.
(Image: AP)
