| A | B |
|---|
| Kepler | German astronomer, mathematician and astrologer |
| Gravitation | the force of attraction between any two masses |
| Third Law | (TA/TB)^2=(rA/rB)^3 (In which Kepler’s law) |
| Second Law | an imaginary line from the Sun to a planet sweeps out equal areas in equal time intervals. |
| First Law | the paths of the planets are ellipses, with the Sun at one focus. |
| Gravitational force | a unit of acceleration equal to the acceleration of gravity at the earth's surface |
| Planet | a similar body revolving about a star other than the sun. |
| Satellites | a natural body that revolves around a planet. |
| Revolution | the orbiting of one heavenly body around another. |
| Self rotation | the movement or path of the earth or a heavenly body turning on its axis. |
| Universe | the totality of known or supposed objects and phenomena throughout space; the cosmos; macrocosm. |
| Inertial mass | the mass of a body as determined by the second law of motion from the acceleration of the body when it is subjected to a force that is not due to gravity. |
| Gravitational field | the attractive effect, considered as extending throughout space, of matter on other matter. |
| Gravitational mass | the mass of a body as measured by its gravitational attraction for other bodies. |
| Orbit | the path traced by an electron revolving around the nucleus of an atom. |
| Orbital period | the time required for a planet (or other celestial body) to orbit once. |
| weightlessness | as a freely falling body or a body acted upon by a force that neutralizes gravitation. |
| deflect | to bend or turn aside; turn from a true course or straight line; swerve. |
| Force | A push or pull |
| Black hole | a deep, immeasurable space into which people or things vanish; an abyss |
| Einstein | Prize in modern physics for the discovery of special relativity and general relativity. |
