The Planetary System from The beauty of the heavens : a pictorial display of the astronomical phenomena of the universe

The beauty of the heavens : a pictorial display of the astronomical phenomena of the universe : one hundred and four coloured scenes, illustrating a familiar lecture on astronomy

The Planetary System

If we had to guess, we’d say you’re reading this from somewhere on planet Earth. The ancient Greeks used the word “planet”, which means wanderer, to describe the huge objects they saw in the sky because they appear to move while the stars in the background appear to stand still. While now we know that everything is moving, including the stars, the name “planet” stuck with us. According to how scientists define the term, there are eight planets in oursolar system, meaning, objects that orbitthe Sun. The sun uses gravity to keep the planets spinning in orbit, and it also provides heat and light to each of them. The four inner planets are Mercury, Venus, Earth, and Mars. Composed of mostly rock and metal and with solid surfaces, these are given the term “terrestiral” or Earth-like. The four outer planets are Jupiter, Saturn, Uranus, and Neptune. They are all much larger than the inner planets; Jupiter is larger than the seven other planets combined! In addition to their size, they also differ from the inner planets in that they have no solid surfaces; they are made of liquid and gases, and they each have a ring system and several moons. Not such a small world, after all.