Throughout the week, three bright planets will line-up along the horizon just after sunset. The brightest of the planets will be Mars. Fresh from its closest approach to Earth in late July, it remains a stunning jewel: a blazing red beacon in the southern sky. Catch it as soon as you can, as it is now receding from Earth and by the end of the month will be roughly two and a half times dimmer than at the beginning. From Mars, begin turning westwards and you will find Saturn. It will not be as bright as Mars and its colour will be a much paler yellow. This planet too is receding from Earth, having made its closest approach to us in late June. Next, continue turning westward until you see the bright white light of Jupiter, setting to the west. Of all the planets on display, it will be the closest to the horizon. These three planets are all further from the Sun than Earth. They are the furthest objects in our solar system that we can see with the naked eye, and have therefore been known since times of antiquity.
Stuart Clark is an astronomy journalist and author of several books about space, both non-fiction and fiction, including The Sky's Dark Labyrinth trilogy