Thousands of years ago, people observed the night sky and recorded their observations in cave paintings and rock art. These early observations were made without telescopes or other devices. The only things early people could see were the phases of the moon and some of the moon’s larger features. They could also see some of the planets and many stars. Then, about 400 years ago, the telescope was invented. It allowed people to observe objects in space in much greater detail.
In 1609, the Italian scientist, Galileo, was probably the first person to use a new invention-the telescope-to observe the sky. A telescope is an instrument that magnifies, or makes larger, distant objects. With this telescope Galileo observed the moon and saw mountains, valleys, and craters that had never been seen before. He also observed the phases of Venus and the four moons orbiting Jupiter. About fifty years later, the English scientist Sir Isaac Newton used an even better telescope so that he could observe other objects in space.
The modern age of space exploration began in 1957, when the former Soviet Union launched Sputnik I, an artificial satellite. A satellite is any natural body, like the moon, or any artificial object that orbits another object. Sputnik, which was about twice the size of a soccer ball, carried instruments to measure the density and temperature of the Earth’s upper atmosphere. The United States launched its own satellite the next year. Soon both countries were launching humans into space.
One of the best-known American space programs was Project Apollo. The Apollo missions landed 12 humans on the moon between 1967 and 1972. These astronauts did experiments and brought back samples of rock. Their work helped scientists learn more about the moon.
In 1977, the Voyager I and Voyager II space probes were launched. A space probe is a robot vehicle used in order to explore deep space. The Voyager space probes sent back pictures of Jupiter, Saturn, Uranus, and Neptune. Both Voyagers are still traveling through space beyond the Solar System.
Other early space probes included Viking I and Viking II, which landed on Mars in 1976, and the Pioneer probes, which used instruments to ‘see’ through thick clouds that cover Venus. Today’s scientists use the Hubble Space Telescope, satellites, and space probes to better understand Earth, the Solar System, and what is beyond.
The launch of the first units of the International Space Station in 1998 began a new era in space exploration. As many as seven scientists at a time will be able to live and work in space. When completed, the station will be nearly 80 meters long and have a mass of more than 455,000 kg. In the future, larger stations could have room for a thousand people or more.
People may one day build places to live on the moon, or even on Mars. Although there have been no plans to build bases on the moon so far, they could be possible by the year 2020. A moon base could be used as a research station. To save money, some materials needed to build and run the base could come from the moon itself. For example, some of the moon’s rocks have oxygen. This oxygen could be taken from the rocks and used by people living on the moon. Recently a probe discovered enough ice at the moon poles to provide a moon base with water. For electricity the base could use solar energy. And some minerals could be mined from the moon and sent back to Earth for processing.