Galileo Galilei didn't invent the telescope, but he did create one that magnified objects about 30 times. One night in 1610, he aimed it at Jupiter—and in the process launched a new era of astronomy. We’ve come a long way since then. The 1930s ushered in telescopes with mirrors more than six feet across, and in 1948 a telescope with an almost 17-foot mirror was unveiled in California. More recently, telescope sizes have expanded to 30 feet and beyond, and the next generation of giant telescopes under construction will exceed 80 feet. The bigger the telescope, the farther and more clearly astronomers can see into space. Here are 5 of the largest optical telescopes in the world, along with significant discoveries made at each one. You can visit all of them.
1. GRAN TELESCOPIO CANARIAS
Located in La Palma, on the Canary Islands, this 10.4 meter or 34-foot telescope, currently the world’s largest, is a Spanish initiative led by the Instituto de Astrofísica de Canarias. The project also involves Mexico’s Instituto de Astronomía de la Universidad Nacional Autónoma de México, Instituto Nacional de Astrofísica, and Óptica y Electrónica, and the University of Florida.
Recently, the GTC participated in identifying microquasar M81 ULS-1, an "ultraluminous source" in the spiral galaxy M81. A microquasar is a massive star paired with a compact star or black hole; the latter has an accretion disk composed of material swirling around it and an intense, variable radio emission. This emission is normally in the form of symmetric jets of matter shooting out in opposite directions. What makes M81 ULS-1 interesting is that the ejected material approaches the speed of light. Only one other microquasar has been discovered with this characteristic (SS433, found in 1979 within the Milky Way). At only some 13 million light years from the Milky Way, its host galaxy, M81, a seventh magnitude object, can be observed with binoculars.
Guided tours include Observatory facilities and the interior of a telescope (which one depends upon availability) along with details on how it works.
2. KECK I AND KECK II
These two 33-foot (10 meter) telescopes dominate the Keck Observatory at 14,000 feet atop Mauna Kea on the island of Hawaii. The first laser guide star adaptive optics system on a large telescope was commissioned on the Keck II in 2004 and helped reveal the black hole at the center of the Milky Way—one of the most significant discoveries in the field of astronomy. More recently, the Keck Observatory helped discover a distant massive galaxy cluster with a core bursting with new stars. SpARCS1049+56 is forming stars at the astonishing rate of more than 800 solar masses per year—800 times faster than in our Milky Way.
Adaptive optics corrects for turbulence in the Earth’s atmosphere using hundreds of actuators that change the shape of deformable mirrors at a rate of 2000 times per second, providing near-perfect detail for planets, stars, and galaxies.
Mauna Kea has a visitor center at 9200 feet with telescopes and guides available. The summit, accessible only by 4-wheel drive, is open from a half-hour before sunrise to a half-hour after sunset.
3. SOUTH AFRICAN LARGE TELESCOPE
Part of the South African Astronomical Observatory, this telescope is the largest in the Southern Hemisphere, with a hexagonal mirror array 36 feet or 11 meters across. It is located at an altitude of 5,770 feet in a remote area of the Northern Cape Province and run by a consortium of international partners from South Africa, the United States, Germany, Poland, India, the United Kingdom and New Zealand.
Astronomers here recently discovered a supermassive black hole in the center of galaxy SAGE0536AGN. Black holes are found in most galaxies, but this one is notable for its size: 30 times more massive than would be expected for a galaxy this size. The black hole’s mass is 350 million times that of our Sun, making it a hundred times more massive than the one in the center of the Milky Way, while the galaxy itself has less mass than our galaxy.
Guided tours of the observatory include exhibits on the radio spectrum (SALT identifies individual stars by the light they emit) and a look at the telescope’s 11 enormous, hexagonal mirrors.
4. HOBBY-EBERLY TELESCOPE
Located at the University of Texas McDonald Observatory in Fort Davis, Texas, this recently refurbished 30-foot telescope is the world's third largest optical telescope and most powerful wide-field spectroscopic one. Astronomers used it in 2012 to measure the most massive black hole ever discovered—the size of 17 billion Suns—in galaxy NGC 1277. Typically, a black hole makes up about 0.1 percent of the mass of its host galaxy, but this one accounts for 14 percent of its galaxy's mass. This and similar discoveries in other galaxies could change current thinking about how black holes and galaxies form and evolve.
There is a visitor center, daily tours of the large telescopes, and star parties three nights a week.
5. ESO VERY LARGE TELESCOPE
Located at Paranal Observatory, part of the European Southern Observatory operations in Chile, the Very Large Telescope array consists of four unit telescopes, each 27 feet or 8.2 meters across, and four auxiliary telescopes 6 feet or 1.8 meters wide, that work together to form the ESO Very Large Telescope Interferometer. It is capable of observing objects four billion times fainter than what can be seen with the naked eye—equivalent to seeing the headlights of a car on the Moon. Among the VLT’s notable discoveries are the first image of an extrasolar planet, tracking of individual stars circling the black hole at the center of the Milky Way, and observing the afterglow of the furthest known gamma-ray burst.
Recently, the VLT recorded details of the spectacular aftermath of a cosmic collision that happened 360 million years ago. Within the resulting debris, images revealed a rare and mysterious young dwarf galaxy, NGC 5291. Dwarf galaxies such as this one are expected to be common in the early universe but are normally too faint and distant to be observed.
Guided tours generally take place every Saturday between 9 a.m. and 2 p.m.