During the twentieth century, people began considering the idea of exploring space as a realistic project. There were many concerns: What would be the effects of weightlessness? Of living without air? What of the effects of cosmic radiation, usually broken up in the high atmosphere?
The Space Age began October 4, 1957. Russia successfully launched Sputnik 1 into space. In 1961, Yuri Gagarin became the first astronaut, completing a circuit of the Earth's orbit in one hour, 48 minutes. Less than a month after Gagarin, NASA launched the Mercury 3, which hops into space with astronaut Alan Shepard for a little over 15 minutes, before splashing down 300 miles from Cape Canaveral.
The side of the moon facing Earth was already very well mapped by the time the Space Age began, but scientists wondered if it was firm enough to support astronauts or spacecraft. Many feared that any craft unfortunate enough to reach the moon's surface would sink in a layer of soft, treacherous dust. Others believed that the moon had "lopsided gravity" which pulled the air and water to the back side, and even wondered if the dark side of the moon might be inhabited.
On October 3, 1959, Luna 3 circled the moon, confirming that the far hemisphere is just as barren and lifeless as our side. The Ranger probes (1961-1965) crash-landed on the moon, sending back photos in their last few moments before impact. Finally, on July 20, 1969, the Apollo 11 transported Neil Armstrong and Buzz Aldrin to the moon's surface. They spent 195 hours in space. Armstrong noted that the great curvature of the moon's surface (four times greater than that of Earth) exaggerated the closeness of the horizon, making it difficult to tell how far away objects were.
Venus presents unique dilemmas for exploration, since we cannot see its surface through the thick clouds in its atmosphere. At its nearest, Venus is 24 million miles from Earth, about 100 times the distance to the moon.
Russia's unmanned probe, Venera 7, was the first to land on Venus, December 15, 1970. It transmitted information back to Earth for 23 minutes before succumbing to the planet's extremely hostile environment. Our most current information comes from Europe's Venus Express, launched from Baikonur Cosmodrome, Kazakhstan in 2005. It spent 500 Earth days circling the planet, a total of two Venus years.
It's surprising that Russian space missions had no luck with Mars, considering they had such good results with Venus. The astronomer Giovanni Schiaparelli mapped the surface of Mars using telescopes in 1888. His drawings of the channels on Mars' surface created the debate that the surface hosted "canals," and possibly liquid water.
NASA's Mariner 4 flew past Mars in 1964 and sent back images which showed that the "canals" are just optical illusions, and confirmed that the air on the surface is too thin to breathe. In 1972, Mariner 9 orbited the planet for one year, sending back over 7000 images. Mankind got their first glimpse of Mars' gorges, dry river beds, and volcanoes (including Olympus Mons, 15 miles tall and three times higher than Mount Everest).
If you're interested in outer space, click here for my previous posts.
There are lots of kick-ass photos from outer space, taken by the Hubble Telescope, here.
If you're really interested, there's an awesome book called Astronomy: A Visual Guide, by Mark A. Garlick.