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The Solar System

Ptolemy first proposed the geocentric model for the solar system (the planets and Sun supposedly orbitied the Earth). He proposed them to orbit in circular orbits. He explained the occasional retrograde motion around Mars using epicycles, but his theory was very complicated and didn't accurately predict the position of the planets. Other early astronomers observed the Universe with the naked eye. They were able to see the Universe as stars emit lights, and planets and moons reflecting light from the Sun. 

Nikolaus Copernicues proposed the heliocentric model for the solar systen (the planets including the Earth orbited the Sun) in the 14th century. He predicted the planets moved around the Sun in circular orbits and the Moon orbited the Earth. He saw that planets that were further away from the Sun travelled more slowly than those closer to it. He also saw that the stars were fixed in a dome beyond Saturn.

Kepler released in the 1600s that the planets had elliptical orbits instead of circular ones - this forms the basis of the model which we use today.

Galileo used a telescope to observe the night sky in the 17th century. He saw mountains on the Moon and saw four moons orbiting Jupiter. This proved the heliocentric to be correct.

Observing the Universe

> in 1850's, photography enabled astronomers to make permenant records of their observations.

> telescopes made it possible to see distant objects as telescopes gather more light than the naked eye; making objects brighter and more magnified.

> today, waves are also used to look deeper into the Universe.

> Hubble Space Telescope takes images using visible light, UV and infrared waves.

> Some space probes take images of distant galaxies and the Milky Way using X-Rays (remember milkyWAY x-RAY

> some space observatories use infrared to produce images. cooler objects emit more infrared than visible light. Infrared light astronomy was used to disocver the Kuiper belt.

Positions of the planets


> between the orbits of Mars and Jupiter, an asteroid belt lies.

> beyond Neptune is a Kuiper belt consisting of several frozen bodies - which is believed to be the source of comets. 

> Oort cloud - the outermost region of the solar system consisting of billions of lumps of rock and ice.

Reflection and Refraction


All waves can be reflected. Sounds waves are reflected in echoes from walls and buildings. Dolphins and bats use reflection to monitor their surroundings through echolocation which uses ultrasound. Radiowaves are reflected from surfaces within the atmosphere such as the ionsphere. 

Light waves will be able to reflect from shiny surfaces when following the laws of reflection:

> the angle of incidence equals the angle of reflection

> the incident ray, the normal and the reflacted ray are all on the same plane

> the incident ray travels towards the normal, reflects off the normal and away from the normal




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