Astronomy revision

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  • Created on: 15-05-14 18:28
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As t ronomy
Newton's Law of Gravity
- All masses are attracted to each other because of the
force of gravity
- Larger mass greater force
- Smaller distance greater force
Gravitational forces at work
- Planets orbit the sun due to gravitational force
- Moons/artificial satellites orbit planets due to gravitational force
- Comets orbit stars due to gravitational force
- Closer planets/planets with greater mass stronger gravitational force
- Larger planet mass greater gravitational field strength
- N.B- Gravitational force: force of attraction between any 2 objects with mass. Gravitational
field strength (g): force acting on an object per unit of mass
Motion in a circle
- Force (directed towards centre of circular path being travelled)
required for objects to travel in a circle
- Orbital speed: 2r / time period (distance / time)
- Galaxy: group of billions of stars (ours is the Milky Way)
- Universe: everything that exists (billions of galaxies)
- The solar system: our sun, its family of planets and their moons
- Moon: satellite which orbits around a planet
- Asteroids = minor planets: lumps of rock orbiting the sun between Mars and Jupiter (=in the
asteroid belt)
- Comet: Snowballs of rock and ice. Elliptical orbit. Tails (melted ice/frozen gases) point away from
Sun due to solar wind. Speed up when near Sun
- Meteor: tiny piece of rock which glows as it burns up as it falls through Earth's atmosphere
- Meteorite: larger lump of rock. Not entirely burnt up as they enter atmosphere. Can create
craters (erosion craters disappear on Earth, no weather on moon craters remain)
- Star: ball of hot hydrogen and helium plasma
Planets in our solar system (in order: closest farthest from Sun)
- Mercury - Jupiter
- Venus - Saturn
- Earth - Uranus
- Mars - Neptune
How we know what the universe is like
- Ptmoley created Earth-centred (geocentric) model
- Copernicus created Sun-centred (heliocentric) model
- Galileo used telescope and observed that Venus had phases like the moon


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