Light
Light travels in a wave motion similar to water waves or ripples. The light we can see, visible light, has a very small wavelength. Lights wavelength is the distance between the peak of one wave to the peak of the next. Visible light has a wavelength of 0.0005mm which is roughly of a millimetre.
Light travels extremely fast- nearly one million times faster than the speed of sound. The speed of light in space or air is almost 300 000 km/s. Light takes 8 minutes to reach Earth from the Sun. A light-year is 9.46 x 1012 km. There is currently nothing that can travel at or faster than the speed of light.
We are unable to see the entire universe due to the fact that it is expanding. Some galaxies, stars and other objects are too far away for light from these objects to reach the Earth which makes it impossible for us to ‘see’ these objects.
Light travels extremely fast- nearly one million times faster than the speed of sound. The speed of light in space or air is almost 300 000 km/s. Light takes 8 minutes to reach Earth from the Sun. A light-year is 9.46 x 1012 km. There is currently nothing that can travel at or faster than the speed of light.
We are unable to see the entire universe due to the fact that it is expanding. Some galaxies, stars and other objects are too far away for light from these objects to reach the Earth which makes it impossible for us to ‘see’ these objects.
The Different Types of Light
Visible light is only one type of light. There are five other types of light, all which have different wavelengths. These types of light, including visible light, are shown on the Electromagnetic Spectrum below.
Gamma rays have the shortest wavelengths. Gamma rays have very penetrating waves and are emitted by some radioactive materials and can be used to kill harmful bacteria, such as sterilising surgical equipment. They can be used to kill certain kinds of cancer but only if used correctly. This is called radiotherapy. If gamma rays are used incorrectly they can damage living cells and cause cancer.
X-rays have the next shortest wavelengths and a very high frequency. They are used to look at bones inside the body and this is possible because they are highly penetrating. Over exposure to x-rays can cause cancer. This is why radiographers stand behind lead screens or wear lead aprons which prevent over-exposure as x-rays cannot penetrate lead.
Ultraviolet rays are emitted by the sun and are what cause our skin to tan. Over exposure to ultraviolet waves can cause skin cancer. Ultraviolet light causes certain chemicals to fluoresce or glow.
Visible light is the only type of light our eyes can see. Visible light is also used to carry messages down optical fibres.
Warm objects give out infra-red waves. Over exposure to infra-red rays cause our skin to burn but not tan. Infra-red rays can be used to let us ‘see in the dark’. Special heat seeking cameras are used by emergency services to detect people trapped in in collapsed buildings. These cameras create an image of an object using the infra-red waves they are emitting.
Some microwaves can pass easily through the Earth’s atmosphere. These microwaves are used for communications such as mobile phones. Microwave ovens use microwaves to cook food. This works because the water molecules inside food absorb the microwaves. They then become ‘hot’ because they vibrate vigorously and the food cooks from the inside. Microwaves can cause damage to living cells if misused.
Radio waves have the longest wavelengths. They are used for communication over long distances. Short wavelength radio waves are used for television as well as FM radio. Longer wavelength radio waves are used for the traditional AM radios.
X-rays have the next shortest wavelengths and a very high frequency. They are used to look at bones inside the body and this is possible because they are highly penetrating. Over exposure to x-rays can cause cancer. This is why radiographers stand behind lead screens or wear lead aprons which prevent over-exposure as x-rays cannot penetrate lead.
Ultraviolet rays are emitted by the sun and are what cause our skin to tan. Over exposure to ultraviolet waves can cause skin cancer. Ultraviolet light causes certain chemicals to fluoresce or glow.
Visible light is the only type of light our eyes can see. Visible light is also used to carry messages down optical fibres.
Warm objects give out infra-red waves. Over exposure to infra-red rays cause our skin to burn but not tan. Infra-red rays can be used to let us ‘see in the dark’. Special heat seeking cameras are used by emergency services to detect people trapped in in collapsed buildings. These cameras create an image of an object using the infra-red waves they are emitting.
Some microwaves can pass easily through the Earth’s atmosphere. These microwaves are used for communications such as mobile phones. Microwave ovens use microwaves to cook food. This works because the water molecules inside food absorb the microwaves. They then become ‘hot’ because they vibrate vigorously and the food cooks from the inside. Microwaves can cause damage to living cells if misused.
Radio waves have the longest wavelengths. They are used for communication over long distances. Short wavelength radio waves are used for television as well as FM radio. Longer wavelength radio waves are used for the traditional AM radios.
History of the Telescope
Galileo Galilei
Galileo Galilei, an Italian astronomer, is considered to be the ‘Father of Modern Astronomy’. He was the first person to use the telescope for astronomical purposes. In 1609 he first turned his telescope to the sky. He built a 3 powered telescope by June or July the same year. By November he looked to the sky with a 20 powered telescope. Galileo discovered craters on the moon as well and 4 of Jupiter’s moons.
Sir Isaac Newton
The next great advance in telescope technology was made by Sir Isaac Newton. Newton Invented a new kind of telescope, a reflector telescope, around 1670. This telescope used a curved mirror to focus light instead of a glass lens. Isaac Newton invented this telescope to correct errors found in earlier telescopes. This new telescope could magnify objects far more times than previous telescope designs.
The Keck
Advances in technology allowed us to build larger and more complex telescopes. The largest Earth-based telescope is the Keck telescope, and there are two of them. They are located on a Hawaiaan volcano- Mauna Kea which is approximately 4200 metres above sea level.
The Hubble
The most advanced telescope in history is the Hubble Space Telescope. The Hubble actually orbits the Earth. The Hubble makes breath-taking discoveries every day that help get a better understanding of the universe.
How Telescopes Work
A refracting telescope depends on the fact that when light passes through glass it slows down and bends. Refracting telescopes have two lenses, one is a converging lens and the other is a diverging lens. The converging lens (also known as objective lens) causes light near the bottom to bend up and light near the top to bend down. At some point in the tube the light beams cross but before they spread out again they hit the diverging lens (also known as eyepiece lens). The diverging lens bends the light beams again, but this time in a straight line towards the eye.
One problem with refracting telescope is that the image is often upside down due to the light beams crossing. As there is no up or down in space this doesn’t matter much, but when using a refracting telescope to view things on Earth they often have another set of lenses to flip the image the right way round.
___________________________________________________________________________________________________________
One problem with refracting telescope is that the image is often upside down due to the light beams crossing. As there is no up or down in space this doesn’t matter much, but when using a refracting telescope to view things on Earth they often have another set of lenses to flip the image the right way round.
___________________________________________________________________________________________________________
Due to the fact that different colours are bent different amounts light can become unfocused when using a refracting telescope. Sir Isaac Newton invented a new kind of telescope, a reflecting telescope that used mirrors instead of lenses.
Light doesn't bend when it hits a mirror, it bounces off. When a light beam hits a mirror it comes of at the same angle it came in. So to speak the angle of the light beam coming in equals the angle out. This is true for all colours.
Light doesn't bend when it hits a mirror, it bounces off. When a light beam hits a mirror it comes of at the same angle it came in. So to speak the angle of the light beam coming in equals the angle out. This is true for all colours.
The primary mirror in a reflecting telescope is curved to bounce the light onto the secondary mirror. The secondary mirror bounces the light through the eyepiece lens, which bends the light into the eye.
How Different Telescopes Contribute to our understanding of
'what is out there'
There are different telescopes that pick up the different types of light as there is no one telescope that can pick up all types of light. Images picked up by the different types of telescopes look very different. However these different images can be used to piece together the invisible universe.
Radio telescopes are used to collect the long radio waves. The atmosphere makes the image fuzzy; however they can be used on Earth.
Far away galaxies, cooler stars and planetary nebula give off infra-red light which is picked up by infra-red telescopes. Infra-red telescopes have to be placed on mountains to reduce fuzziness caused by low lying water vapour.
Optical telescopes pick up visible light. These telescopes are used on Earth look into space or from space to look further into space or back at the Earth.
Ultraviolet telescopes have to be placed outside our atmosphere. This is because the atmosphere blocks out some wavelengths of ultraviolet light. Ultraviolet telescopes pick up ultraviolet light emitted from the sun, other stars and galaxies.
X-ray wavelengths, due to being quite short, can’t pass through Earth’s atmosphere. X-ray telescopes have to be placed outside of the atmosphere to be able to pick up the x-rays. Dwarf stars, the moon and galaxy clusters give of x-rays.
To pick up the high frequency light waves of gamma rays a gamma ray telescope has to be placed well out of the atmosphere. Gamma rays are emitted by supernova, black holes and neutron stars.
Radio telescopes are used to collect the long radio waves. The atmosphere makes the image fuzzy; however they can be used on Earth.
Far away galaxies, cooler stars and planetary nebula give off infra-red light which is picked up by infra-red telescopes. Infra-red telescopes have to be placed on mountains to reduce fuzziness caused by low lying water vapour.
Optical telescopes pick up visible light. These telescopes are used on Earth look into space or from space to look further into space or back at the Earth.
Ultraviolet telescopes have to be placed outside our atmosphere. This is because the atmosphere blocks out some wavelengths of ultraviolet light. Ultraviolet telescopes pick up ultraviolet light emitted from the sun, other stars and galaxies.
X-ray wavelengths, due to being quite short, can’t pass through Earth’s atmosphere. X-ray telescopes have to be placed outside of the atmosphere to be able to pick up the x-rays. Dwarf stars, the moon and galaxy clusters give of x-rays.
To pick up the high frequency light waves of gamma rays a gamma ray telescope has to be placed well out of the atmosphere. Gamma rays are emitted by supernova, black holes and neutron stars.
Bibliography For This Page
Schmidtke, K 2012, ‘Light’, Mercy College, Mackay, 15 September 2012.
Schmidtke, K 2012, ‘Telescopes’, Mercy College, Mackay, 15 September 2012.
Schmidtke, K 2012, ‘We need different types of telescopes to see the light’, Mercy College, Mackay, 15 September 2012.
Roby, J 2012, ‘The History of the Telescope’, viewed 15 September 2012
<http://www.astronomy-for-kids-online.com/thehistoryofthetelescope.html>
Schmidtke, K 2012, ‘Telescopes’, Mercy College, Mackay, 15 September 2012.
Schmidtke, K 2012, ‘We need different types of telescopes to see the light’, Mercy College, Mackay, 15 September 2012.
Roby, J 2012, ‘The History of the Telescope’, viewed 15 September 2012
<http://www.astronomy-for-kids-online.com/thehistoryofthetelescope.html>