(18 Read and complete.
1 The ancient Greeks
2 Look! 50 aliens
3 Robots
4 William Herschel
5 The astronauts
6 The Moon
almost once every month.
7 It was 1969 when Neil Armstrong
(walk) on the Moon.
8 People
they want to look at the planets.
(call) the Sun Helios.
(come) out of the spaceship.
(explore) Mars now to find information.
(discover) Uranus in 1781.
(leave) for the Moon tomorrow.
(travel around the Earth
(use) telescopes when