Topic 7 - Astronomy

• Weight formula: W = mg, where Weight (Newtons, N) = mass (kilograms, kg) x acceleration due to gravity (metres per second, m/s)
• Greater value of g

  Results in greater weight of the object
• Greater mass of the planet

  Results in a greater value of g on that planet
• Components of Our Solar System

  • The Sun, Eight planets, Natural satellites, Dwarf planets, Asteroids, Comets
• Planets in Our Solar System

  • Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
• Larger planets have rings

  Due to their strong gravitational field attracting debris
• Solar System Model

  Initial geocentric model with Earth at the centre, then heliocentric model with the sun at the centre
• Planetary Orbits

  Gravitational force causes the planet to change direction constantly, speed is constant but velocity changes, force causes acceleration without increasing speed
• For a stable orbit

  If the planet moves closer to the sun, gravitational attraction increases, force, acceleration, and velocity increase, orbital speed increases
• Red Shift: Light appears red shifted from galaxies moving away from Earth
• Red Shift increases as the distance away from Earth increases, evidence of an expanding universe
• Explanation of Red Shift

  As the universe expands, galaxies move away, light from galaxies has its wavelength red-shifted, frequency appears to decrease
• Evidence for the Big Bang: Red Shift shows the universe is expanding, CMB (Cosmic Microwave Background)
• Red Shift

  Frequency appears to decrease as the source (galaxy) emitting the wavelength is further away, showing the universe is expanding
• Red Shift indicates the universe is expanding
• The universe must have been formed from a single point initially based on Red Shift
• Evidence for the Big Bang

  • Red Shift
  • CMB (Cosmic Microwave Background radiation)
• CMB stands for Cosmic Microwave Background radiation
• Formation of CMB

  When the universe was very young, everything, the first stars and rock, would be very hot and emit short-wavelength radiation. This radiation, as the universe expanded, would have been stretched to become microwaves. This background radiation is present wherever you point a telescope in the sky, proving the hot young universe has cooled and expanded since
• The Big Bang accounts for all the experimental evidence and is the most accepted model currently
• Steady State Theory states that as the universe expands, matter is constantly being created, maintaining a constant density of matter
• Observable universe is suggested to be the same at any time and any place according to the Steady State Theory
• Steady State Theory cannot be correct as different stars were present at different eras of the universe, showing evolution
• Steady State Theory does not account for CMB
• Life Cycle of a Star

  Dust and gas cloud present in a galaxy, interstellar matter clumps together to form nebulae where stars are formed. Gravitational attraction draws particles together, cloud becomes more concentrated, temperature and pressure increase, fusion occurs creating a star which stays stable for billions of years. Eventually, the star runs out of gas to fuse, leading to collapse. If massive, it produces a supernova and forms a neutron star or black hole. If normal-sized, it swells to produce a red giant star, then contracts and cools into a white dwarf
• Observations of the universe can use any wavelength in the EM spectrum
• Telescopes measuring X rays, Gamma, UV need to be outside the atmosphere as these wavelengths do not reach the ground
• Technological advances allowed other parts of the EM spectrum to be measured and collected