Waves & The Universe

Waves & The Universe

1. The Universe

   • Ancient astronomers made detailed observations of the univerese using the naked eye. They worked out that the stars were further away than the planets but decided that they were also in a fixed shell- all of which were the same distance away.
     • They could also see patches of fuzzy light which are actually nebulae
   • Using a telescope, Galileo Galilei (1564-1642), discovered that the milky way and some nebulae were actually groups of stars. He also suggested that stars were suns at different dstances from earth.
   • As more and more telescopes with greater magnification properties began to develop, astronomers made more observations of the Solar System. Astronomers in Galileo's time could only observe about six planets, but now we know that the Solar System contains 8 planets, (Mercury, Venus, Earth, Mars, Saturn, Uranus, Jupiter, Neptune) as well as several dwarf planets, moons and asteroid bodies.
     • We also now know that the sun is one of the billions of stars which make up our galaxy- The Milky Way. The universe is made up of billions of galaxies too. Some of the nebulae we see are actually galaxies
       • Telescopes have also been used to tell us how far away and how big each of the planets are.

2. Spectrometers

   • Light from the sun is a mixture of different colours. This called a spectrum. However some of the gases in the sun' atmosphere absorb some of the loght, and cause black lines in the spectrum. Gases in the earth's atmosphere can also do this.
   • Visible light s also a mixture o light with different wavelengths and frequencies. These different wavelengths can be split up using a prism, DVD, CD or anything that contains lots of fine lines in it. A device which can split up wavelenghts is called a spectrometer.

3. Exploring the Universe

   • Early telescopes let astronomers see objects which emitted visible light. When photography was invented he amount of data that could be gathered by these telescopes increased. Objects which are too far away can be photographed by a camera on a telescope for several hours. Modern telescopes use phtography tp find and ana;yse new objects in space. Spectrometers can also be attached to analyse the different wavelengths of light given off by different objects.
   • Most objects which astronomers observe, emit energy from all parts of the electromagnetic spectrum (radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays). So to find out more about these objects, telescopes have been designed to detect most of the electromagentic spectrum, rather than just visible light. These different wavelengths tel us more about the objects we are observing.
   • The Hubble space telescope has been orbtting Earth since 1990. It produces very clear images of stars and galaxies, because it is above earth's atmosphere. This is because it means that light waves aren't refracted or reflected by clouds, dust or any other movements in the atmosphere. Other telescopes are put into orbit for many of the same reasons.

4. Alien Life??

   • In 1976 two Viking landers touched down on Mars. They checked the soil for chemical changes that might have been caused by living organisms. Only one of the experiments showed such changes. It was decided that there was now evidence for life. All the life which we are aware of, depends on water. Scientists are looking for evidence to prove if there was or is water on plantes inside our solar system. Space probes orbiting Mars have photographed channels which could have only been formed by water in the past, on Mars.The Phoenix lander discovered frozen water in the martian soil in 2008.
   • Scientists have discovered planets orbiting other stars. These are too far away to observe properly with telescopes, but scientists can sometimes find out about gases produced on the planets
   • Some of the electromagnetic radiation that we use for communication travels out into space and could be detected by intelligent life. Alien civilisations may be able to send back signals similar to these. SETI is a programme which runs these experiments.

5. Life Cycles of Star

   • A nebula is a cloud of dust and gases (mostly hydrogen). Star form when a nebula is pulled together by gravity. A the contracting cloud gets more dense, it heats up and may begin to glow. As more and more mass is contracted, the cloud's gravitational pull gets stronger and more material is compressed compressed. This is called a PROTOSTAR. Eventually the temperature and pressure in the center of the protostar will become high enough to force hydrogen nuclei to fuse together to form helium. Fusion reactions like this create a lot of energy as electromagnetic radiation. The outward pressure from hot gases just balances the compresson due to gravty. The star is now in the main-sequence part of it's life cycle.
     • Stars of similar sizes to our Sun are low mass stars. They remain stable for about 10 billion years, until they have fused most of their hydrogen into helium. When this happens, the core of the star is not ht enough to withstand gravity, and the star collapses. Tthe outer layers will then expand to form a RED GIANT. This is much larger than the original star.
       • Other fusion reactions happen inside the red giants. The star will remain as a red giant for about a billion years before throwing off its outer layers. The rest of the will be pulled together by gravity and will collapse to form a white dwarf. Eventually it will cool and become a black dwarf.
     • Stars with a considerably greater mass than the sun are hotter and bigger. They fuse all the elements up to iron. They do this much faster than main sequence stars and become red super giants, once fusion is finished. At the end of the red super giant period, the star will rapidly collapse and then explode. This explosion is called a supernova. In this explosion, the outer layers of the super giant are cast off and expand outward. If what is left is four times the mass of the sun, gravity will pull the remains together to form a black hole. If not it will become a neutron star.

6. Theories about the Universe

   • If a source of light is moving away, the light we detect will have a longer wavelength than expected. This is called red shift, because it means that the light has been shifted to the red end of the spectrum.
     • Red Shift supports both of the theories for how the universe was formed- the Big Bang Theory and the Steady State theory. This is because both predict that the universe would be expanding, and this is what red shift proves.
   • The big bang theory says that everything started in one tiny concentrated point about 13.5 billion years ago. The univrese then expanded from this point, and is still expanding. As the universe continued to expand, gravity would have cause mass to clump togethr and form stars.
     • Another piece of evidence which supports this theory is that to astronomers who were building a radio telescope, detected microwave signals coming from everywhere. This supports the Big Bang Theory because it says that at the beginning of the universe masses of microwave radiation would have been produced.
   • An alternative theory is the Steady State theory. This theory says that the universe has always existed and has merely been expanding. New matter is constantly created whilst the universe expands. This is the less supported theory, because there is less evidence for it.

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