Looking into space
For thousands of years, humans have told stories to explain the lights in the night sky. Even the earliest stargazers recognized that many of the objects that they could see behaved differently from each other, but it was in ancient Greece – from around the 6th century BCE – that astronomy began to be systematized. Greek astronomers drew up formal lists of constellations, developed a scale of magnitude to describe the brightness of stars, and made attempts to model the paths of the planets. Following the invention of the telescope in 1608, physical differences between the various objects began to become more apparent, leading to an explosion in scientific knowledge
The Universe is full of objects, large and small. Many of the closest bodies in our Solar System – asteroids, planets, and moons – are made visible by reflected sunlight. They move against a seemingly fixed background of more distant objects: luminous stars, glowing nebulae, and remote galaxies.
Our Solar System
The region of space governed by the Sun – and everything contained within it – is known as the Solar System. It encompasses eight major planets, at least five dwarf planets, and a wealth of smaller bodies.
How the Solar System formed
Our Solar System emerged from a collapsing disc of material that was in orbit around the newborn Sun some 4.6 billion years ago. Mid-sized bodies called planetesimals gradually formed, and eventually developed into today’s planets.
Kepler’s laws of planetary motion
Three laws, discovered by Johannes Kepler between 1609 and 1619, govern the behaviour of planets orbiting the Sun, or any object in an elliptical orbit around another. They reflect the changing influence of gravity with distance.
Solar System planets size and scale
Earth is the largest of the rocky planets in the inner part of the Solar System, but it is dwarfed in size by the gas giants found in the outer region. These, in turn, are relatively tiny when compared with the vast size of our Sun.
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