SCALES: PLANETARY Problem for Astronomers: there is no sense of depth from looking at the sky. Comet Hale-Bopp: 10 light-minutes away Andromeda Galaxy: 2 million light-years away Proximity on the sky does not tell us about proximity in space. If two stars appear equally bright, one could be luminous and far and the other feeble and near. Apparent size does not tell us about proximity in space. If two monks appear equal size, one could be adult and far and the other young and near. Sun and Moon have equal angles in the sky. Work in groups to set your expectations of the size of the Solar System and nearby stars. If the Earth is the size of small lime how far away and how big are: Moon, Sun, Jupiter, edge of the Solar System, and nearby stars? A SCALE MODEL Star A large, glowing ball of gas that generates heat and light through nuclear fusion. Planet Mars Neptune A moderately large object which orbits a star; it shines only by reflected light. Planets may be rocky, icy, and small, or large and gaseous in composition. Moon An object that orbits a planet. Also can be called a satellite. The largest moons are as large as the smallest planets. Ganymede (orbits Jupiter) Asteroid A relatively small and rocky object that orbits a star. Gaspra Comet A relatively small and icy object that orbits a star on an elliptical orbit. Hyukatake Earth shrunk from 13,000km to 4cm That’s a factor of 300,000,000 or 300 million Astronomers measure length in meters, astronomical units, and parsecs. Distance from Earth to Sun = 150 billion meters = 1.5 X 1011 meters = 1 astronomical unit (AU) Terrestrial Planets = 10,000 km Diam. Giant Planets = 10x Terrestrial Planets Solar-type Stars = 10x Giant Planets Sun is >99% of all Solar System mass >99% in star <1% in sum of planets, asteroids, meteors & comets Properties of the Sun (a star) Earth ↑ Diameter = 1.4 million kilometers = 100 × Earth diameter Mass = 2 × 1030 kilograms = 330,000 × Earth mass Age = 4.6 billion years SPACE SCALE MODEL: Just like a map of the Earth, this model of a solar system shrinks it to a manageable size, a 1:300,000,000 scale. • • • • • The Moon is a grape at 1m distance The Sun is a 4m sphere 450 m away Jupiter is a 0.5m ball 2.5km from Sun Neptune is a 15cm ball 15 km away The nearest star is 150,000 km away TIME SCALE MODEL: And at this scale, light is reduced to very fast walking speed. There’s no way information in the universe can travel any faster than this. • • • • The Moon is a seconds walk away The Sun is 8 minutes walk away 5 hours to walk the Solar System Years to walk to the nearest stars The Solar System is Empty Science isThere Seeing is the Sun and not much else in the entire volume of the Solar System. In the scale model, that is 30 m3 in a volume of space 3 trillion m3 so only one part in 100 billion has anything.