How does Gemini compare with the Hubble Space Telescope?
A large state-of-the-art ground-based telescope such as Gemini can be built for about a thirtieth of the cost of the Hubble Space Telescope. When equipment fails in space it is expensive to replace: each Space Shuttle flight costs about US$500 million. In addition, the time lag between designing the instruments and launching them can mean that some technologies have become dated by the time they are used in space. It is difficult to launch into orbit a telescope with a mirror larger than 4 m in diameter. An 8-m telescope such as Gemini is about 10 times more sensitive to light than a 4-m telescope. A big, sensitive telescope is essential for certain kinds of work, such as studying the light of faint stars and distant galaxies to determine their properties (such as mass, age and chemical composition).
