astrophysics

• the universe is a large collection of billions of galaxies
• a galaxy is a large collection of stars
• our solar system consists of planets, dwarf planets, moons, artificial satellites, asteroids and comets
• gravity provides the force that creates orbits
• the planets move around the sun in almost circular orbits
• there is a force that acts towards the sun in the centre of the circle
• the object is already moving so the force just causes it to change direction
• the force is gravity that helps all the objects orbit the sun
• the larger the mass of the object is the stronger the gravitational field
• speed = distance/time
• stars start as clouds of dust and gas called a nebula
• the force of gravity pulls the dust and gas together to create a protostar
• after protostar the star turns into a main sequence star which is caused by thermal expansion
• main sequence stars then turn into red giants and then into white dwarfs
• big stars explode into a supernova
• a black hole's gravitational pull is so strong that nothing can escape it, not even light.