On June 17-18, Mars and Mercury will appear together in the sky, separated by less than half the width of the full Moon. It will be the closest apparent approach of any two planets for the year. Such events are often only visible to early risers, but this is one that many people should be able to witness with ease, weather permitting.
Two planets, or a planet and a star, appearing to line up to us are known as conjunctions. Most planetary conjunctions are a degree or two apart, but that can still make for a spectacular site. Next week, however, Mars and Mercury will have less than a quarter of a degree between them – putting them in the same field of view of a telescope.
Better still, the approach will take place while Mercury is close to its best position for viewing – it will be at its furthest east of the Sun on June 23.
Nevertheless, this will still be an event that is easy to miss, which is why we're giving you some warning. The planetary pair will be lowish in the west as the Sun sets, and get lower still as the sky gets darker. Even with a good view west there will only be a narrow window between when the sky is dark enough and when they are too low to see.
Binoculars or a home telescope will be ideal for this, but neither is required. Even from a highly polluted part of a city, the two planets should be visible, their closeness emphasizing the difference in color. Obviously, the further you can get away from bright lights, the better they will look.
Mars will be a long way from its brightest. Were it not for the conjunction with Mercury this wouldn't be a time it would attract much attention. Even a decent-sized backyard telescope that might reveal the polar ice caps at other times will only show a small red disk.
As the pair sets, you may wish to turn your eyes to Jupiter, which will have just passed its brightest for the year days before. Besides the dance of its four bright moons, you may even get a last look at the Great Red Spot, which is showing signs of disappearing after swirling away for at least 400 years.
You won't be able to see Saturn at the same time as the Mars-Mercury conjunction, but it will be rising shortly after they set, and even with a just-past-full Moon running some interference, will be a beautiful sight.