10/2AstronomyKepler•Came up with 3 rules for the planetary systemKepler’s Laws1.Planetary orbits are ellipses with the sun at one focus (the other focus contains no 2.The radius vector sweeps through equal areas in equal times 3. P2 a3 KP2= a3 (special version) P2= a310/11Comet•Since only part of an orbit it seen, it is unknown what shape•Escape velocity must be calculated to find the shape of the orbit•All comets seen are concluded to be part of the solar systemOrbits•Part of everyday life•Falling objects are orbiting the EarthWeightlessness•Force of gravity is weight on Earth•F= (Gmemo)/(Re2)•Are astronauts experiencing weightlessness actually weightless?•Astronauts are falling all the time together, so there is no net force between them and the surrounding objects.Mass•Solar mass unit created to be mass of sun•Mass of the sun is 300,000 times mass of EarthRotary motion•All planets turn on axis counter clockwise except Venus (clockwise) and Uranus (on its side)•Handedness Outline of the UniverseThe Solar System- 8 planets and 1 dwarf planet orbiting around the Sun, which is the closest star to us. Its main source of energy is heat, from the nuclear reactions going on in its interior. Within the Solar System there are also asteroids, comets, dust and gas. Basically, the definition of the Solar System is the Sun and all that is gravitationally bound to it.-Mercury- 3/10-4/10 AU-Venus- 7/10 AU-*Earth-*Mars-*Jupiter- many, many moons-*Saturn- prominent ring system-*Uranus-*Neptune-(*Pluto- demoted to a dwarf planet)* denotes satellites-“Planet” comes from the Greek word for ‘wandering star’. The Greeks didn’t see the Earth as a planet because it wasn’t in the sky, and they saw the Sun as a planet because it wasin the sky. The original 7 planets for them were the Sun, Mercury, Venus, Mars, Jupiter, Saturn, and the Moon.~it is possible that the days of the week were named after the names for the original 7 planets.Distance, time, speed of light (scales: AU, ly)Distancefor astronomers is measured in AUs, or Astronomical Units. This is an arbitrary unit determined by ancient astronomers. They decided that the distance from the Earth to the Sun was one AU. An AU is actually about 150,000,000,000 m, or approx. 93 million miles. We now get the distance to the Sun by bouncing radar off of Venus and timing how long it takes to come back.