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People thought about the stars long before we had telescopes. Greek scientists such as Aristotle (384–322 B.C.) and Ptolemy (A.D. 100–165) said that the Sun traveled around Earth.
This seemed so clear that few questioned it. Then, in 1543, Polish astronomer Nicolaus Copernicus said that Earth actually traveled around the Sun. For many decades, people tried to prove him right or wrong. The telescope was the key to finding the answer. Telescopes have become more sophisticated since then. They have expanded our knowledge beyond Copernicus’s dreams.
1609
◀ Italian scientist Galileo Galilei hears about the new Dutch instrument for seeing far. He builds one himself and points it skyward. He quickly sees that Copernicus was right. For instance, people who say Earth is the center of the universe like to say that no other planet has a moon. That proves Earth is special, they say. But with a telescope, Galileo finds four moons orbiting Jupiter (today we know it has many more!). His discoveries make telescopes popular in Europe. But he also upsets popular religious beliefs. In 1633, the Roman Catholic Church makes him reject his own scientific conclusions.
1663
Scottish astronomer James Gregory (right) builds a reflecting telescope. It uses mirrors instead of lenses. Five years later, Isaac Newton improves the design, creating the Newtonian telescope. ▶
1733
◀ English mathematician Chester Moor Hall improves refracting telescopes. He puts two different types of glass together. This creates a lens that keeps colors from separating. That stops the rainbow ring around images.
1781
William Herschel, an English astronomer, discovers the planet Uranus with his own telescope. He soon builds the world’s first giant reflector. Its mirror is 48 inches wide. His sister Caroline uses it to discover eight comets. ▶
1814
◀ German lens maker Joseph von Fraunhofer notices something while looking through a telescope. He sees dark lines within the spectrum of visible light. Later, scientists realize these lines can be useful. They allow us to figure out the temperature of stars and what chemicals they contain.
1835
Baron Justus von Liebig, a German chemist, makes larger reflecting telescopes possible by inventing the modern mirror. It is a piece of glass with a thin silver coating. Before this, mirrors were made of shiny metal and were very heavy. ▶
1845
◀ William Parsons, the Third Earl of Rosse, builds a reflecting telescope on his estate in Ireland. It has a 72-inch mirror. It remains the world’s biggest reflecting telescope until 1917. That’s when the 100-inch Hooker telescope is built near Los Angeles.
1889
George Ellery Hale invents the spectroheliograph. This instrument reveals details of the Sun’s surface. Hale later builds some of the world’s biggest telescopes. Among them is the largest refractor in the world, the Hale Telescope on Palomar Mountain in California. ▶
1932
◀ Bell Labs engineer Karl Jansky wants to find why noise is blocking radio signals. He learns the noise comes from space. That’s how he invents radio astronomy—by accident.
1957
The Soviet Union (now Russia) launches Sputnik, the first human-made satellite. This leads to satellites and probes carrying telescopes. In 1959, Russia’s Luna 3 first shows the far side of the Moon. ▶
1960s
◀ The world sees advances in detecting infrared, ultraviolet, X-rays, and other invisible radiation. These developments create new ways to study the universe. Pictured here is Earth shown in ultraviolet.
1980s
Mirrors larger than 15 feet wide sag under their own weight. That bends their images. Engineers find two ways to solve this. One way is to use a honeycomb structure to support the mirror. The other is to make one mirror out of many smaller mirrors. ▶
1990s
◀ NASA launches the Hubble Space Telescope, one of the largest observatories in space. It is named after astronomer Edwin Hubble (left). NASA also launches the Chandra X-Ray Observatory.
2000s
The Spitzer Space Telescope (right) is launched. It is used to detect infrared light. The Swift telescope is also sent into orbit, to scan the skies for mysterious, ultrabright flashes known as gamma-ray bursts. These bursts are the most powerful explosions in the universe. ▶
2010s
◀ The Hisaki ultraviolet telescope is launched. Its mission is to study the atmospheres of Venus, Mars, and Jupiter’s moon Io. The Giai observatory (left) is also launched. Its job is to map up to a billion stars in the Milky Way galaxy.
2020s
The James Webb Space Telescope is launched. Its images provide the deepest and sharpest pictures of the universe ever seen. They include light from one galaxy that traveled 13.1 billion years before it was observed. ▶
