The Five Planets
The ancients had beautifully dark skies, dusted with thousands of stars of varying brightness. At some point, they noticed that five of these stars were quite different from the rest. Not only were they conspicuously bright, but they also moved against the background of the sky, while all the rest were fixed in place. These movements weren’t all at the same speed, and varied over time, so these special stars became known as “Planets“, from the greek word for “Wanderer”. The Romans eventually named them for five of their gods – Mercury, Venus, Mars, Jupiter and Saturn. The next planet in line, Uranus, is also visible to the naked eye, but only just — it is so faint that it can’t be distinguished from the background sprinkling of faint stars, and it is no surprise that nobody ever noticed it. Ancient stargazers noticed that for all their mysterious movements, the planets were bound to stay within a strip of sky which formed a ring all the way around. This area happened to be neatly populated with twelve distinct constellations, which we recognise today as the signs of the Zodiac. The association of planets with gods probably played a large part in the birth of Astrology as a tool to try predict the actions of the gods, and thus everything the gods affected.
Of the five Solar System planets, Venus is the easiest to find, and the most obvious. Within a few hours of either sunset or sunrise (depending on where Venus is in it’s orbit), you will see a very bright star above the area where the sun set (or will soon rise). It is unmistakable and far outshines anything else in the sky apart from the Sun, the Moon, and the International Space Station (ISS). Despite Mercury also being very bright, it is also the most difficult of the five to see. It is so close to the sun, that it is never visible at night, and must be glimpsed through the glow of sunset or sunrise. Occasionally conditions are right that we can see it during twilight. Because both of these planets are closer to the Sun than Earth, they appear bound to the Sun, never to travel far from it.
The remaining three, however, have no such limitation. Mars is bright, and shines with a dull orange-red colour. Jupiter is more than twice the distance from the Sun as Mars, but is vastly bigger, and so is a lot brighter. It shines with a clear white light, and it’s four major moons can even be seen through binoculars. Saturn is fainter again, and has a yellow-brown colour, and the rings can be also be seen through the most basic telescope.
Thanks to the work of Johannes Kepler and Isaac Newton, we are able to predict the position of all the planets with great accuracy, and tables of these predictions can be found in any astronomical almanac or magazine. But best of all, they are all easy naked eye objects and perfectly suited for urban astronomy. Get to know them well, and you’ll be able to amaze (and eventually bore) your friends and family by pointing out a star and saying “Oh, by the way, that’s Jupiter”