From Spyglasses to Hubble
Galileo Galilei peers at the cosmos through a telescope circa 1620, as seen in a modern drawing. (History buffs take note: The carved ebony-and-ivory mounting, now a famous part of Galileo's telescope, was actually made in 1677.)
Just over 400 years ago, Galileo--then chair of mathematics at Italy's University of Padua--got word that Dutch glass makers had invented a device that allowed viewers to see very distant objects as if they were nearby.
The mathematician soon acquired a Dutch instrument, and on August 25, 1609, he presented an improved, more powerful telescope of his own design to the senate of the city-state of Venice. The government officials were so impressed with Galileo's telescope that they rewarded the professor with a higher salary and tenure for life at his university.
At the time, Galileo was touting the telescope for commercial and military applications, such as watching ships at sea. But in the fall of 1609 Galileo turned his telescope to the heavens, setting into motion a new kind of science: telescopic astronomy.
Galileo wasn't the only 17th-century scientist making his mark on the telescope. In 1671 Sir Isaac Newton developed a new version of the instrument (pictured) that used mirrors instead of lenses to focus the light from distant objects.
Newton's reflecting telescope got rid of the halo of light surrounding target objects that had plagued lens-based telescopes. His new design also allowed telescopes to do the same work with shorter bodies.
As telescope technology improved, scientists found ways to create ever larger designs. The 100-inch (254-centimeter) Hooker telescope at California's Mount Wilson Observatory first collected light from the heavens in November 1917.
The telescope's mirror helped astronomer Edwin Hubble--seen above looking through the telescope's eyepiece in 1937--to find new ways of measuring how far away objects are from Earth. Hubble's findings ultimately allowed him to confirm that the universe is expanding
Not all telescopes rely on light visible to the human eye. The Arecibo Observatory in Puerto Rico for example, is the world's largest single-dish radio telescope. Its 1,000-foot (305-meter) dish, seen above in May 2007, has been collecting radio waves from space objects since 1963.
Radio astronomy allows scientists to see objects and actions that would otherwise be invisible to humans, such as pulsars, black holes, and stars and planets shrouded by dust.
The Hubble Space Telescope, one of NASA's longest running science missions, was released into orbit in 1990 by the space shuttle Discovery (pictured, the 1990 release). As of August 2009, the telescope is still returning images of the universe that dazzle astronomers and the public alike.
But Hubble is about more than pretty pictures: The space telescope has helped astronomers make a number of ground-breaking discoveries, from confirming that black holes exist to discovering new rings around Uranus.
Back on Earth, bigger and better optical telescopes have been rivaling space-based observatories for the sharpness of their cosmic vision, and Hawaii's Mauna Kea volcano is arguably the mecca of ground-based astronomy.
Thirteen telescopes sit within shouting distance atop the 13,780-foot-high (4,200-meter-high) summit, and a 14th--the massive Thirty Meter Telescope--is slated to open in 2018. (Examine the plans for the world's biggest telescope.)
Like Galileo's telescope, the Chandra X-ray Observatory is also celebrating an anniversary in 2009: The space telescope was sent into orbit on July 23, 1999 (above, Chandra sails into orbit just after deployment from the space shuttle Columbia).
Ten years later Chandra's mission is still a "go," returning pictures and data that illuminate parts of the universe invisible to the human eye.