What is light and how does it travel?
What is Light?
Light is an electromagnetic wave - a wave of electric and magnetic energy oscillating very quickly. There are many different types of of electromagnetic waves and they are determined by how fast they oscillate eg. radio waves have a slower oscillation rate compared to something like X-rays or Gamma Rays which have a much quicker rate of oscillation. These electromanetic waves travel in pockets called Photons. Because light travels in both waves and and photon pockets, it behaves both like a wave and a particle.
How does Light travel from the Sun to Earth?
Most waves require a medium to travel in. For example if a rock is dropped into a source of water it will make waves in it but without the water there are no waves. However because light consists of Photons it can travel through space like a stream of miniscule particles. When travelling through space the Photons actually travel faster and lose less energy because there are no molecules in the way to slow it down. Light from the Sun will always be in a straight line because of the light frequencies. Once the light hits Earth's atmosphere it begins to collide with gas molecules. The photons with larger wavelengths such as red, orange and yellow can travel right through the gas molecules. However photons with a colour of green, blue or purple of much shorter wave lengths allowing them to be easily absorbed by the gas molecules found in out atmosphere. These molecules will only hold onto the photons for an instant before shooting them back out in a random direction.This occurrence is why the sky looks blue and make it seem to glow due to the scattered photons flying towards the Earth.
How long does it take light to reach the Earth?
The distance between the sun and Earth is around 150 million km and light travels at 300,000 km/s which if worked out mathematically would end taking 8 minutes and 20 seconds for sunlight to reach Earth directly from the Sun.
Telescopes:
Galileo - Galileo used a very early and basic refracting telescope to do all his work studying which later on gave him his fame. He was the man who discovered that Earth was not the centre of the universe. He also discovered Jupiter's four main moons and the rings of Saturn. He also was able to observe that Venus had a face like the moon, this was all done with the one single refracting telescope!
Refracting Telescope:
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Refracting telescopes works just like a magnifying glass except it is used to view distant objects instead of things close up. This is the oldest style of telescope, which in it's basic form as was used by Galileo 400 years ago is just a simple curved lens which focuses light to a point. These types of telescopes use lenses to gather light and focus it to the eyepiece. The objective lens is located at the front of the telescope and the eyepiece at the rear. A dutch optician by the name of Hans Lippershey designed and made the first refracting telescope in 1608.
Reflecting Telescope:
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Reflecting telescopes use curved mirrors instead of convex lenses to collect and focus light unlike the refracting telescope. A large concave mirror which has a center that is thinner than the edges which collects and reflects the light to make an image. Once the image is formed from the reflection the lens in the eyepiece magnifies the image. The larger ones can see objects a millionth or billionth the brightness of the faintest star that can be seen by the naked eye, making it very useful to observe dark or dim objects in space. A Scottish astonomer by the name of James Gregory came up with the design of for the reflecting telescope in 1663 although Isaac Newton was the first person to make the model of this telescope in 1688.
Radio Telescope:
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Radio telescopes are used to study naturally occurring radio emission from stars, galaxies, quasars, and other astronomical objects between wavelengths of about 10 metres (30 megahertz [MHz]) and 1 millimeter (300 gigahertz [GHz]). At wavelengths longer than about 20 centimeters (1.5 GHz), irregularities in the ionosphere distort the incoming signals. The radio telescope has a large dish which reflects the incoming radio waves towards the tip located in front of the concave face. It also has a box located at the back behind the dish which amplifies and detects radio signals.Karl Jansky was the first man to discover radio waves in 1931. However in the the late 1930's an American engineer by the name of Grote Reber built the first bowl shaped telescope and operated it in his own backyard. His homemade telescope collected and measured radio waves given off by objects in space.