The world's first major astronomical observatory had no telescope. Although it featured some of the best and most accurate instruments ever built, they simply made it easier to do what astronomers had been doing for centuries: map the night sky by plotting the positions of the stars and planets.
The observatory, known as Uraniborg ("Castle of the Heavens"), was built by Danish astronomer Tycho Brahe, one of the most gifted skywatchers in history. He designed and built more than a dozen major instruments for Uraniborg and a second observatory, Stjerneborg ("Castle of the Stars"), next door.
The instruments included sextants (though without any glass optics), quadrants, armillary spheres, and others. All were tools for plotting the positions of astronomical objects. Some measured an object's altitude above the horizon or its direction in the sky, while others measured angles between two target objects.
With these instruments, Tycho produced the most accurate and detailed star atlases to date. He also precisely plotted the positions of planets as they moved back and forth across the sky. Johannes Kepler later used these catalogs to devise the laws that explain how planets move around the Sun, confirming the view that Earth is not the center of the universe.
Yet Tycho's instruments were basically finely crafted extensions of the human eye. They could see no deeper into space and no more clearly than the eye alone. Thus, their ability to improve human understanding of the universe were limited.
That ability improved dramatically in the 17th century with the invention of what is still the mainstay of astronomical research: the telescope.
Using these assemblages of metal tubes and glass lenses, some of the giants of modern science revolutionized our knowledge of the universe around us and our place in it. And they set the stage for more dramatic discoveries in the centuries ahead.
Key dates and inventions in the quest to see deeper into the universe.
Hans Lippershey invents a ‘looker,’ the first confirmed telescope, by aligning two lenses inside a metal tube.
Using a telescope of his own construction, Galileo Galilei studies planets, the Moon, the Milky Way, and other astronomical objects, igniting a scientific revolution.
Isaac Newton reveals a new type of telescope, which uses polished mirrors instead of glass lenses.
Grinding glass to the right shape for refracting telescope lenses was a daunting task, and Galileo’s telescopes produced a slightly blurry view of the sky, with colored “haloes” around astronomical objects. And the glass contained chemical impurities that colored the lenses green.
Isaac Newton, who is best known for devising his laws of motion and gravity, realized that part of the problem was with the glass itself. Any glass lens acts like a prism, splitting a beam of light into its individual wavelengths or colors, so there was no way to eliminate the colored haloes with lens-based telescopes.
So Newton devised a new type of telescope, which he presented to his colleagues in England’s Royal Society in January 1672. Instead of glass lenses, Newton’s telescope used two polished metal mirrors.
The primary mirror, at the bottom of the telescope tube, curved inward slightly, in a spherical shape. (In other words, if you extend the curve of the mirror into space, it will form a sphere.) Light from an astronomical object struck this mirror and reflected back up the telescope tube, where it hit a flat secondary mirror. This mirror, which was tilted at a 45-degree angle, in turn reflected the light to an eyepiece at the side of the tube, where the observer saw an image of the star, planet, or other astronomical object.
Although it took a while to work out some problems and gain acceptance by most astronomers, Newton’s creation of the reflecting telescope ushered in a new era of astronomical study. By the early 18th century, most astronomers were using reflectors, and although refractors made a brief comeback a century later, all large modern-day research telescopes are reflectors, and Newtonian-style reflectors are popular among amateur astronomers.
The Life of Isaac Newton, Richard S. Westfall (Cambridge, 1993)