What is a telescope? How they work: Follow the light through a telescope using Ray Diagrams. What Instruments are used? What is image data? Where are the best places for telescopes? The problems with the Atmosphere. Satellite telescopes. A virtual tour of the Telescopes of the World. Information about Space Probes. A Glossary of terms.
National Schools'Observatory
It holds us down on the Earth, and the Moon in orbit around the Earth.
The more massive and closer an object is, the greater its gravitational pull or attraction.