Physicists (including Astronomers) study matter, space, time, energy, forces and fields and the interrelationship between these physical phenomena to further understand the laws governing the behaviour of the universe, and seek to apply these laws to solve practical problems and discover new information about the earth and the universe.
You need a bachelor degree in science majoring in physics or nanotechnology to work as a Physicist (including Astronomer). It is also common to complete postgraduate studies.