Introduction to Astronomy
The Solar System
- The solar system consists of our sun, eight planets with their moons, dwarfs planets, asteroids, comets, and other celestial bodies.
- The planets are orbiting around the sun in paths known as elliptical orbits.
- The four inner planets (Mercury, Venus, Earth, Mars) also referred to as terrestrial planets, are made primarily of rock and metal.
- The four outer planets (Jupiter, Saturn, Uranus, Neptune), called gas giants and ice giants, are composed largely of gases and hold numerous moons.
Stars and Galaxies
- A star, like the Sun, is a hot sphere of gas that emits light and energy generated through nuclear reactions.
- Stars of different sizes, ages and temperatures have different colours. The hottest stars are white or blue, while the cooler stars are red.
- All the stars we see at night are located in our own galaxy, the Milky Way.
- There are billions of galaxies in the Universe, some of which are spiral-shaped like the Milky Way, while others are elliptical or irregular in shape.
The Universe
- The universe is the entirety of space and time, and all matter and energy in it.
- The universe is believed to have originated around 13.8 billion years ago in the Big Bang.
- The universe has been expanding since its formation, a concept known as the expanding universe theory.
- Dark matter is hypothesised to make up about 85% of the matter in the universe.
- Dark energy, a mysterious form of energy, is thought to be responsible for the acceleration in the expansion of the universe.
Observational Astronomy
- Telescopes are used to observe distant objects in space, with some collecting visible light and others collecting different types of electromagnetic radiation.
- Radio astronomy uses large antennas to detect radio waves from space.
- Space probes are robotic spacecraft sent away from Earth to explore other planets and celestial bodies up close.
Key Astronomers
- Nicolaus Copernicus first proposed that the Earth revolves around the sun, contradicting the long-held belief that Earth was the centre of the Universe.
- Galileo Galilei is known for improvements to the telescope that enabled detailed observations of the planets, leading him to support Copernicus's model.
- Edwin Hubble discovered that there are many galaxies outside the Milky Way and provided substantial evidence of the expanding universe.