Core Physics

Geocentric - Earth Centred

• Proposed by Ptolemy
• Earth was at the centre of the solar system
• Everything moved around the Earth in circular orbits
• Only featured - Mercury, Venus, Mars, Saturn, Jupiter

Heliocentric - Sun Centred

• Proposed by Nikolaus Copernicus
• Sun was at the centre of the solar sytem 
• Planets moved around the Sun in circular orbits
• Planets further away from the sun move slower than the ones closer
• Stars were in a fixed dome beyond Saturn
• Featured 6 planets - all except Neptune and Uranus
• Galileo Galilei provided evidence to support this theory
• Both had no telescopes - only naked eye

Galileo Galilei

• Used a telescope to see - mountains on the moon and four moons orbiting Jupiter

Reflection

• When light bounces off a boundary between different materials
• All waves can be reflected (echoes)
• Redio waves are reflected off sufaces within the atmosphere
• angle i = angle r - incidence angle = reflected angle

Refraction

• The bending of light at a surface
• All waves are refracted at the boundary between two different materials
• Speed of the wave changes as it passes through different materials
• Less dense - More dense = light bends towards the normal
• More dense - Less dense = light bends away form the normal
• Light speed depends on material density

Reflecting telescope

• Converging eyepiece lens, Concave mirror, Flat mirror
• Concave mirror forms an image of a distant object and flat mirror reflects the image to the eyepiece lens
• Lighter and easy to manouvere 
• Produce better quality images than reflecting telescopes

Refracting telescope

• Converging objective and eyepiece lens
• Objective lens converges an image of a distant object to a focal point
• Eyepiece lens magnifies the image

Converging Lens

• Fatter in the middle
• Used in - telescopes, cameras, binoculars, projectors, eyes
• Rays of light that are paralell to the the principal axis are refracted inwards
• Rays of light are refracted to the focal point - principal focus
• Distance from the centre of the lens to the focal point = focal length
• Fatter lens = Shorter focal length

Diverging lens is thinner in the middle

Focal Length

• When the distance between the object and lens is more than 2 focal lengths, the image will be - real , diminished and inverted
• When the distance between the object and lens is less than 2 focal lengths, the image will be - real, diminished and magnified
• When the distance between the object and lens is less than the focal length, the image will be- virtual, upright and magnified - magnifying glass

Diminished - smaller than the object
Inverted - upside down
Real - can be projected onto a screen

Spectometer

• White light is split up into the visible spectrum using refraction through a glass prism
• A spectometer is a device used to look at the visible spectrum

Sources of light

• Hot stars emit blue light and cooler stars emit red light
• Some electromagnetic waves are absorbed by gases in the atmosphere more than others
• Visible light is not well absorbed - but large telescopes are located on top of high mountains where the air is thinner - to get the best quality image
• The chemical composition of stars is idnetified using a spectometer to analyse the light they emit
• Modern telescopes have built in spectometers

Atmosphere

• EM waves are absorbed bu=y the atmosphere, some more than others
• X rays and Gamma rays are almost all absorbed by the atmosphere
• Radio waves are not absorbed - used for communication

• As a police car passes the sound changes from high pitch when it is approaching and low pitch when it is moving away
• This is because the sound waves are being squashed together when approaching and stretched when moving away
• The Doppler Effect is observed for all waves
• It is observed in light emitted from stars
• The wavelength decreases and frequency increases as a star moves towards an observer - blue shift
• The wavelength increase and frequency decreases as a star moves away from an observer - red shift 

The faster the object is moving - the greater the Doppler Effect will be