Understanding Our Solar System
Following the invention of the telescope, astronomers were able to view fainter objects – objects that were smaller or further away, or both!
Until 1781, astronomers only knew about five planets other than Earth – the ones visible with the naked eye: Mercury, Venus, Mars, Jupiter and Saturn. William Herschel then discovered Uranus. This was the first planet to be discovered using a telescope. Neptune was discovered around 1845. British and French astronomers were both credited with finding the 8th planet. They had independently calculated where it would be, based on observations of the orbit of Uranus.
In 1655 Dutch astronomer Christiaan Huygens observed Saturn using a refracting telescope he had designed. He made the most accurate description of Saturn for the time, saying Saturn had a thin, flat ring. He also discovered Saturn’s largest moon, Titan.
Pluto was discovered in 1930 and declared the 9th planet of the Solar System. Twenty-five years previously, American astronomer Percival Lowell had predicted Pluto’s existence. In 2005 astronomers discovered the dwarf planet Eris, along with several other small objects in the Kuiper belt. This led to scientists reclassifying Pluto as a dwarf planet in 2006.
In 1801 Italian astronomer Giuseppe Piazzi made the first observation of an object in the asteroid belt. He named it Ceres. This ‘asteroid’ had since been reclassified as a dwarf planet. Less than two years later, German astronomer Henrich Olbers discovered the asteroid, Pallas. In 1802 William Herschel suggested the name ‘asteroids’ for this new group of objects. We now know there are hundreds of thousands of asteroids between the orbits of Mars and Jupiter. The expression ‘asteroid belt’ has been used for this area of the Solar System since the 1850s.