Astronomy Revision.pdf

Astronomy Revision History of Astronomy Astronomers names 1. Early Astronomers They knew about the wanderers and that the moon reflected sunlight. Explained the phases of the Moon and lunar eclipses. 2. Aristotle First offered evidence of the curved shadow of the Earth as...

Astronomy Revision History of Astronomy Astronomers names 1. Early Astronomers They knew about the wanderers and that the moon reflected sunlight. Explained the phases of the Moon and lunar eclipses. 2. Aristotle First offered evidence of the curved shadow of the Earth as proof of the idea that the Earth was a sphere. 3. Aristarchus Proposed a heliocentric model of the universe and that the Sun was further away from the Earth than the Moon. 4. Eratosthenes Calculated that the Earth had a circumference of about 46,000 km. 5. Hipparchus First to start classifying the stars and dividing them into six groups based on their brightness. 6. Ptolemy Supported the geocentric model of the universe which became known as the Ptolemaic model. 7. Nicolas Copernicus Made many observations and concluded that the sun was the centre of the universe. 8. Johannes Kepler Used the observations of Tycho Brahe to derive three laws of planetary motion. 9. Galileo Galilei Invented and used the first telescope to make many of his observations. He also discovered the first four moons of Jupiter and saw them change their position over a few hours. 10. Sir Isaac Newton First astronomer to apply mathematics to his observations. He co-invented calculus and advances in the study of light and physics. 11. William Herschel Discovered the planet Uranus using a telescope. 12. Edwin Hubble Found that some of the clouds were not gas clouds in our galaxy but were other huge galaxies of billions of stars way beyond the milky way. He also found that all the galaxies were moving away from each other. Name the fiver wanderers known to early astronomers Mercury, Venus, Mars, Jupiter and Saturn Early astronomers believed the earth was the centre of the universe. What is the name of this model? Geocentric Model which is the model that as the earth at the centre of the solar system Copernicus proposed the heliocentric model of the solar system. Describe the structure of this model. It is a cosmological model in which places the sun at the centre of the solar system, with Earth and other planets orbiting around it. The Origins of the Universe Big Bang Theory The universe began about 13.7 billion years ago with a huge explosion of pure energy. The idea that the universe began as just a single point, then expanded and stretched to grow as large as it now. This theory describes how the universe expanded from an initial state of high density and temperature. It was first proposed by George Lemaitre. This theory is supported by two pieces of evidence. Hubble’s law and Cosmic Microwave Background Radiation. Timeline of the Big Bang The big bang occurs and singularity Time began exists. (t=0) Time and space had begun. Space was t=10-43 s expanding quickly. The universe had expanded to about the t=-34 s size of a cricket ball. Light matter forms and tiny particles such as electrons and positrons are formed, Protons and neutrons formed from t= 1/10000 s collisions between smaller particles. The universe was still expanding and t=1/100 s cooling rapidly, the same size as our solar system. There was still no such thing as an atom. Universe more than 10 trillion kilometres t=1 s across. Cooled to about 10 billion degrees Celsius. The nuclei of hydrogen, helium and t= 5 minutes lithium had formed among a sea of electrons. Universe has cooled to 3000 C. The first t= 300,000 years atoms are formed. The first stars appear t= 200 million years The first Galaxies form and first Planets. t= 1 billion years Neutral atoms were not formed during the first five minutes of the big bang because there isn’t enough energy for nuclei to fuse together into heavier combinations. Steady State Theory The steady state theory of bondi, gold and hoyle says that although the universe is expanding it has no beginning and no end. The theory says that new matter must be continuously created to keep the average density of matter unchanged. The amount of new matter required is low and would not be detectable. How will the Universe end? It will end in three ways: Big Freeze Theory The theory states that the Universe could end. The universe and other isolated systems, entropy will increase until it reaches a maximum value. After this the heat in the system will be distributed evenly. This means there will be no room for usable energy and the universe will die from heat death. Big Rip This theory claims the Universe will end with a big rip. The pull of the Universe's expansion gets stronger than the gravity it contains. This would tear apart galaxies, followed by black holes. Earth and humanity could slowly decay into radiation, collapse in on itself or be ripped apart. Big Bounce In the theory, the universe is expanding and contracting in a massively big-picture timeline. It is based on the idea that gravity becomes repulsive at very high densities. Preventing a singularity and causing a bounce instead of a bang. Objects in the Universe Universe - The universe is commonly defined as the totality of everything that exists Star - A star is a luminous ball of gas, mostly hydrogen and helium held together by its own gravity Planet - A planet is a celestial body that orbits around the sun or another star. Moon - Moon is a celestial body that makes an orbit around a planet and is the only natural satellite of Earth Galaxy - Galaxy is a large group of stars that rotate around a central massive object. Black hole - A black hole is an astronomical object with a gravitational pull which is really strong Constellation - A constellation is a group of stars in the sky that form a certain pattern Comet - Comet is a large object made of dust and ice that orbit the sun which are leftovers from the formation of the solar system Asteroid - Asteroid is small, rocky, object that orbit the sun which were leftover from the formation of the Solar System Nebula - Nebula is a cloud of dust, hydrogen, helium and other gases which are the birthplace of stars Types Galaxies Spirals - Appear as flat, blue - white disks of stars, gas and dust. These galaxies are divided into two groups: normal spirals and barred spirals. Spirals are actively forming stars and comprise a large fraction of all the galaxies in the local universe. The milky way is also a spiral galaxy. Ellipticals - Account for about one -third of the galaxies. They possess little gas and dust, contain older stars and are not actively forming stars anymore. The largest ellipticals are called giant ellipticals. Irregular - Have very little dust and are neither disk or elliptical. These galaxies were abundant in the early universe, before spirals and ellipticals developed. Stars Star Classification - Spectral Classes Class Surface Star Colour Example Description Temperature O 30,000 - Blue Naos Hot and 60,000 K Luminous B 10,000 - Blue Rigel Very Luminous 30,000 K A 7,500 - 10,000 White Deneb More common K F 6,000 - 7,500 K White Fomalhaut Powerful and (Yellowish) average size G 5,000 - 6,000 Yellow (like the Sun Well-known K Sun) K 3,500 - 5,000 K Orange Arcturus Cooler M 2,000 - 3,500 K Red Proxima Common Centauri and Antares  1. Main Sequence Stars These stars' energy comes from nuclear fusion, as they convert Hydrogen and Helium. The hotter the stars are, the brighter they are. The Sun is a typical main Sequence star. Dwarf Stars They are relatively small stars. There are two types: Red Dwarf: small, cool and very faint Yellow Dwarf: small 2. Giant and Supergiant Stars - Old, Large stars Red Giant Is a large star and is frequently the colour orange. It is a relatively small old star and has become cooler. Blue Giant They live for a short time because they burn fuel (helium) very fast and are a large star. SuperGiant Is the largest known type of star and is rare. When they die they explode as supernova and become black holes. 3. Faint, Virtually Dead Stars White Dwarf It is a small, very dense, hot star that is made mostly of carbon. They remain after a red giant star loses its outer layers. Brown Dwarf It is not very luminous and is a star whose mass is too small to have a nuclear fusion occur at its core (the temperature pressure at its core is too low for fusion). Neutron Star Is a very small, super-dense star and has intense pressure which forces electrons and protons together to form neutrons. It has a thin atmosphere of hydrogen. Pulsar Is a rapidly spinning neutron star that emits energy in pulses. Stars Life cycle The Hertzsprung - Russell Diagram How stars end