b) Comets have highly eccentric orbits, which can take them far beyond Pluto. Sometimes they will be seen, and then disappear for thousands of years before being sighted again.
c) Comets travel fastest nearest the Sun, often travelling up to 15 miles a second.
4a) The Sun produces energy through nuclear fusion. This is when hydrogen atoms are broken down and the particles move around at high speeds. This causes the hydrogen atoms to join to form helium. Mass is lost in the process and reappears as energy.
Hydrogen Nuclear Fusion Helium + ENERGY
b) Billions of years ago, as small cloud of gas and dust began to compress under its own weight. Particles within the cloud's centre became so densely packed that they often collided and stuck (fused) together. The fusion process released tremendous amounts of heat and light, which could then combat the compressing force of gravity; eventually, the two forces became equal. The balance of fusion reactions versus gravitational collapse, which, occurred in this little cloud is referred to as a star.
c) The life of a star like our Sun lasts about 10, 000 million years. It is a yellow dwarf for most of its life, like the Sun that we know. When all the hydrogen is used up, the helium is used as a fuel, which produces much heavier elements such as oxygen. The result of this is that it expands and cools to form a red giant. Then the star uses up all its fuel, and collapses forming a white dwarf, which is a million times denser than water. When this cools it becomes a black dwarf.
Our Sun is a small star. Larger stars have a very different life to it. It has a shorter life as it is hotter and burns up the fuel quicker. It starts off as a blue giant, but when it runs out of fuel it cools and expands to form a red super giant. In the same way as smaller stars it becomes unstable and collapses but in this case, blows off its outer layer in a great explosion called a supernova. The blasts fires out many elements, which eventually form new stars. Then the supernova collapses to a very dense neutron star. However if it still has a big mass it continues to collapse under its own gravity. The pull of gravity then becomes so strong that not even light can escape it. This is known as a black hole.
5a) A galaxy is a large collection of stars all gravitationally interacting and orbiting around a common centre.
b) The name of our galaxy is the Milky Way.
6a) As of yet, there have been no places outside Earth that have the right conditions in order to sustain life have been discovered. However, we have only explored a tiny amount of the Universe, and so it is possible that there may be places as yet undiscovered that are capable of sustaining life. Scientists have discovered possible traces of water on Mars and Europa, one of the moons of Jupiter could have oceans with marine creatures living there.
b) Currently, the Voyager is travelling in the galaxy with information about humans, in case some extra-terrestrials would find it, and could learn about humans. Also, radio waves are beamed in to space in the hope that they will be picked up by aliens, who will in turn, beam back their own radio waves, in order to make contact.
7a) About 15 billion years ago a tremendous explosion started the expansion of the universe. This explosion is known as the Big Bang. At the point of this event all of the matter and energy of space was contained at one point. It is not known what existed before the Big Bang. The Big Bang was actually an explosion of space within itself unlike an explosion of a bomb were fragments are thrown outward. The Big Bang lay the foundations for the universe.
b) Red shift is when the spectrum lines of the galaxies are shifted to redder wavelengths.
The Cosmic Microwave Background (CMB) is a relic of the early Universe and was a cooled remnant of the primeval fireball – an echo of the Big Bang. If the Universe was once very hot and dense, a plasma would have formed coupled with the radiation within the Universe. As the Universe expanded and cooled, there came a point (about 100,000 years after the Big Bang) when the radiation split from the matter. The radiation cooled and is now 2.7 degrees above absolute zero (2.7 Kelvin). The spectrum of the CMB is what scientists would describe as being almost exactly that of a ‘black body’ (a perfect radiator).
c) Because the spectrum of the CMB is like that of a black body, it could not have been created by prosaic means which completely contradicts the Steady State Theory and can not be explained using this theory. However, it does match the Big Bang Theory as it appears to have been created as a consequence of the Big Bang.
8) Both the history and the future of the Universe depend on its mass and whether the expansion rate of the Universe will be slowed by its own mass. The mass of the Universe also controls the growth of hierarchical structure, including the collapse of material in to dense virialised regions associated with galaxies.