The telescope is the oldest and probably the most effective tool to 13 ______ space. It has been used by astronomers since the 16th century and it has tremendously changed our knowledge of the universe. Certainly, the telescope itself has changed a 14 ______ since that time too.

The most famous telescope nowadays, the Hubble Telescope, works in space, in 15 ______ Earth orbit. It works from above the atmosphere of the Earth and that is why it 16 ______ fantastically clear photos. The Hubble was 17 ______ into space on 24th April, 1990 from the Space Shuttle Discovery and is still in operation. Scientists say its information could help them to 18 ______ the mystery of the black holes and to understand how they form.