Studying the sky
Astronomy is the science of studying objects in space, such as stars, planets, moons and galaxies. It is one of the oldest sciences. Long ago, people watched the sky with only their eyes and used the stars to tell the time, find directions and plan farming seasons.
Changing models of the universe
Early thinkers believed in the geocentric model, which placed Earth at the centre of everything, with the Sun and planets moving around it. Later, the astronomer Nicolaus Copernicus proposed the heliocentric model, which correctly places the Sun at the centre, with Earth and the other planets orbiting it.
Key idea
Geocentric = Earth at the centre (old, incorrect). Heliocentric = Sun at the centre (modern, correct). Better tools helped scientists change from one model to the other.
The telescope changes everything
The biggest step forward was the invention of the telescope, a tool that collects light to make distant objects look nearer and clearer. Galileo Galilei was among the first to point a telescope at the sky. He saw mountains on the Moon and four moons circling Jupiter, giving strong evidence for the heliocentric idea.
Example
An optical telescope collects visible light. A refracting telescope uses lenses, while a reflecting telescope uses curved mirrors to gather light.
Today astronomers also use radio telescopes that detect radio waves, and space telescopes placed above the atmosphere for a clearer view. Buildings that house these instruments are called observatories.
Remember
- Astronomy is the study of objects in space.
- Copernicus supported the Sun-centred (heliocentric) model.
- The telescope let humans see far more detail in the sky.