8 - Space Physics

• Artificial Satellites: Man-made satellites that have been sent into space for purposes such as satellite imaging and communications
• Big Bang Theory: The currently accepted model for the origin of the universe, suggesting that the universe has expanded from an initially very small, hot and dense point
• Circular Orbits: Planets and satellites travel in circular orbits, with gravity providing the required force for these orbits.
• Dark Energy: A hypothesised form of energy, believed to be responsible for the universe’s ever increasing rate of expansion
• Dark Mass: A hypothesised type of mass that cannot be observed by current methods, used to explain why some galaxies rotate faster than they should for their observed mass
• Main Sequence Star: The stable state of all stars, where the gravitational forces pulling the star together, and the pressure pushing outwards, are balanced
• Milky Way Galaxy: The galaxy in which our solar system is located
• Natural Satellites: The moons that orbit planets
• Nebula: A cloud of dust and gas
• Protostar: The first stage all stars go through after forming from a nebula, where the star becomes hot enough for hydrogen nuclei to fuse
• Within our solar system, there is one star, the Sun, plus the eight planets and the dwarf planets that orbit around the Sun.
• Red Giant Star: When their hydrogen is used up and larger nuclei are produced by fusion, stars of a similar magnitude to the Sun will expand to form a red giant
• Natural satellites, such as the moons that orbit planets, are also part of the solar system.
• The sun lies at the centre of our solar system, it is heliocentric.
• Red-Shift: The observed increase in the wavelength of the light emitted by distant galaxies, with the more distant the galaxy, the faster it is moving and so the bigger the observed increase in wavelength
• Dwarf planets also orbit the sun, including Pluto and Ceres.
• Star Life Cycle: The stages that a star passes through in its lifetime, dependent on the size of the star relative to the sun
• There are also asteroids and comets in our solar system.
• Our solar system is a small part of the Milky Way galaxy.
• Sun: A star formed from a cloud of dust and gas being pulled together by gravitational attraction, with fusion reactions occurring in the sun.
• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto are the planets in our solar system.
• Supernova: The explosion of a massive star, that distributes the elements created by the fusion reactions in the star, throughout the universe
• Smaller planets are made of primarily rock, while the larger planets are primarily gas.
• All planets orbit the Sun on the same plane.
• White Dwarf: When the fusion reactions in stars of a similar magnitude to the sun come to an end, the star will contract under gravity and cool down to form a white dwarf
• All planets rotate, just at different speeds.
• The orbital radius of a planet decreases as the gravitational attraction to the sun increases, causing the orbital speed of the planet to increase.
• The release of energy from fusion opposes the collapsing of the cloud due to gravity, maintaining an equilibrium where the energy released due to fusion balances the pressure of gravitational collapse.
• Fusion occurs as the light (mainly hydrogen gas) nuclei fuse together to form helium nuclei, creating a large amount of energy.
• The gravitational attraction between the gas/dust particles draws them together, causing the cloud to become more concentrated.
• A star has now formed, and it will stay like this for billions of years.
• Eventually the star runs out of gas to fuse, causing it to collapse, increasing the pressure and temperature of the core, meaning heavier elements can fuse.
• The life cycle of a star begins with a dust and gas cloud present in a galaxy.
• The temperature and pressure of the cloud increase as the particles get pushed so close together, eventually causing the pressure to be so great that the gas/dust particles are able to fuse together.
• Some planets rotate in the opposite direction or on a skewed axis to the other planets, and this may be due to past collisions throwing its axis off balance.
• Larger planets have rings, as their gravitational field is so strong it attracts debris.
• In the Solar System Model, Earth was initially at the centre, with the planets, our moon, and the sun, orbiting the Earth.
• The heliocentric model was formed 600 years later, with the sun at the centre, based on Mars’ “retrograde motion”, Galileo observing moons orbiting Jupiter, and Kepler showing that the planets orbited in ellipses, not circles.
• As the planet orbits the sun, the gravitational force causes the planet to change direction constantly, moving in a circle around the sun.
• This constant change in direction means the velocity is always changing, causing the planet to accelerate without increasing its speed.