The Solar System🪐
Models Of The Solar System
The ancient Greeks used a geocentric model of the Solar System, proposed by Ptolemy. In the geocentric model, the Earth was in the centre and everything else (the planets, Moon, Sun and stars) moved around the Earth in circular cycles. Ptolemy's model was very complicated and did not accurately predict the position of the planets.
In the 14th century, Nikolaus Copernicus proposed a heliocentric model. This stated that:
- The Sun was at the centre of the Solar System
- The planets moved around the Sun in circular orbits and the Moon orbited the Earth
- The planets further away from the Sun travelled more slowly than ones close to it
- The stars were fixed in a dome beyond Saturn
The heliocentric model explained Mars's retrograde motion. However, it still did not accurately predict the position of the planets because Copernicus used circular orbits.
- In the 1600's, Johannes Kepler realised that the planets had elliptical orbits. This model forms the basis for the one that we use today.
- In the 17th century Galileo Galilei first observed the night sky using a telescope. He saw mountains on the Moon and four moons orbiting Jupiter. These observations provided proof that the heliocentric model of the Solar System was correct.
Observation of the Universe✨
Early astronomers observed the Universe with the naked eye. Stars are visible because they emit light, but planets and moons reflect light from the Sun.
The invention of the telescope made it possible to see more distant objects, because telescopes gather more light, making objects gathered and more magnified. In the 1850's, photography enabled astronomers to make permanent records of their observations.
Today, waves, other than light, are used to look deeper into the universe. The Sun is at the centre of our Solar System and is orbited by the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. An asteroid belt lies between the orbits of Mars and Jupiter.
The Kuiper belt consists of several frozen bodies orbiting beyond Neptune. It is believed to be the source of comets. The outermost region of the Solar System is known as the Oort cloud. This consists of billions of lumps of rocks and ice. The Hubble space telescope takes photos using visible light as well as infrared and ultraviolet waves. You will have to know about this telescope in I/GCSE Physics.
Some space probes take images of distant galaxies and the Milky Way using X-rays. Some space observatories use infrared to produce images. Cooler objects emit more infrared than visible light. Infrared astronomy was used to discover the Kuiper belt.
Reference: https://solarsystem.nasa.gov/internal_resources/3253
Drafted by Catrina (Physics)