Where to Go

Part of the Astronomers' Universe book series (ASTRONOM)

Going anywhere in space involves crossing enormous distances. The Moon is about 385,000 kilometres away and took the Apollo spacecraft over three days to get there. The Mars Reconnaissance Orbiter took about seven months to reach Mars. As everything is moving in relation to everything else there are times when an object is closer and therefore easier to reach than other times. Missions to objects in our solar system must therefore be well planned. Most missions outside of a low Earth orbit are for scientific research, and aim to provide answers to many of the questions we have about solar system objects and the history and formation of the solar system.

The distance between the Sun and the Earth is about 150,000,000 kilometres. This distance is also known as an Astronomical Unit or one AU. The heliopause is thought to be about 100 Astronomical Units away from the Sun, and no man-made craft have yet crossed this boundary. Proxima Centauri, which is the next nearest star to us, is over 266,000 Astronomical Units away. Light from our Sun takes about eight minutes to reach the Earth and 4.2 years to reach Proxima Centauri. With current technology, spacecraft can only travel at a small fraction of the speed of light, and so it would take thousands of years to reach another star and currently there are no missions planned to explore other star systems.


Solar Wind Solar System Solar Flare White Dwarf Impact Crater 
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© Springer Science+Business Media, LLC 2008

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