Visible Light and the Solar System

Solar system
1. Heliocentric - Sun is at the centre of the solar system.
2. Geocentric - The earth is that the centre of the solar system. It was accepted because peope could not feel the earth moving or in motion.
3. Our solar system is called the Milky Way.
4. Planets (from closest to the sun): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
5. Galileo observed that Jupiter had four moons around Jupiter. He checked another time and noticed the moons has moved. This meant that the moons were orbiting Jupiter and therefore proving the geocentric model wrong.
Waves
1. Transverse waves: - The pattern of disturbance is at right angles to the direction of movement. The oscillation of transverse wave is perpendicular to the direction of energy transfer. E.g. Electromagnetic wave and secondary earthquakes. These do not need a medium to travel through
2. Longitudinal waves: - The pattern of disturbance is in the same direction as the direction of wave movement. The oscillation is parallel to the direction of energy transfer. These need a medium to travel through.
3. Waves are regular patterns of disturbance. They transfer energy and information from one point to another without any transfer of matter. Waves can be produced in ropes, springs and on the surface of the water.
4. Amplitude is the maximum vertical disturbance caused by a wave e.g. its height.
5. Wavelength is the distance between corresponding points on two successive disturbances.
6. Frequency is the number of waves produced (or passing a particular point) in one second.
Refraction
1. When a ray of visible or infrared light travels from glass, perspex or water into air, it is refracted (changes direction)
Reflection
1. Some light is also reflected from the boundary. The angle of incidence = the angle of reflection.
Wave speed
1. Wave speed (m/s) = Frequency (Hz) x Wavelength (m)
  1. Wave speed (m/s) = Distance (m) / Time taken (s)
Observing the universe/ Telescopes
1. Before Galileo's discoveries in 1610, all observations were made by the unaided or naked eye. This had many drawbacks because what can be seen with the naked eye depends on the weather and the quality of the individuals eye sight. In cities, light pollution can also be a problem
2. A simple telescope consists of two different converging lenses. A converging lens is made of perspex or glass with two curved surfaces, thicker in the middle than at the edges. This shape allows the lens to bring together (converge) light into a focus by refracting it.
3. The distance from the middle of the lens to the focus is called the focal length. If the lens is held up to the light (e.g. a window), an inverted image (of the window) can be seen on a piece of paper held on the other side. An image that can be projected onto a screen is said to be a real image.
  1. The piece of paper or the lens can be moved until the image is sharp (focused). The distance from the lens to the image is the focal length, which can be measured. For a given type of glass, the thickness of the lens will determine its focal length - so a thicker lens means a shorter focal length.
4. A simple telescope can be expensive to make large, good quality lenses which is why the first successful reflecting telescope was built in 1668, it had two mirrors and an eyepiece.
5. Objective lens: - Collects light to form an image.
6. Eye piece: - Magnifies the image.

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Visible Light and the Solar System

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