Astronomical Objects

This lesson covers: 

  1. Understanding that the universe encompasses all existing matter and energy
  2. Defining our solar system and its key components
  3. Explaining elliptic and circular orbits of planets, comets and asteroids

The scale of the universe

  • The universe constitutes everything that exists, both visible and invisible. This spans glowing stars to unseen dark matter.
  • Our Milky Way galaxy is a gravitationally bound cluster of stars, planets, gas and dust.
  • At the centre of our galaxy is our solar system - the Sun and all objects orbiting it.

Components of our solar system

Diagram showing the components of our solar system including the Sun, Venus, Mercury, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Our solar system includes:

  • The Sun - The star at the centre of our solar system.
  • Planets - There are 8 major planets orbiting the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
  • Dwarf planets - Pluto and other smaller planet-like bodies.
  • Moons - Natural satellites like our Moon orbiting planets.
  • Asteroids - Rocky objects mostly found in the asteroid belt between Mars and Jupiter.
  • Comets - Structures made of ice and dust that have elliptical orbits around the sun.

The nature of orbits

Diagram showing the orbits of Jupiter, Earth, and Saturn around the Sun, with Halley's comet following a highly elliptical orbit.
  • The 8 major planets approximately follow circular orbits around the Sun.
  • Comets typically have highly elliptical orbits, with periods lasting millions of years.
  • Some shorter-period comets like Halley's comet (76 year orbit) originate closer in.
  • The asteroid belt occupies the space between Mars and Jupiter.