Mars and Earth are about to pass closer together than at any time in almost 60,000 years.
On Wednesday at 1051 BST (0951 GMT) the two planets will be 56 million kilometres (35 million miles) apart - about the closest they can get.
Mars has been visible as a bright orange object in the night sky for many weeks.
Mars will be visible in the southern sky
It currently outshines any other celestial body except the Moon and Venus.
Sir Patrick Moore, presenter of the BBC's Sky at Night, said: "You can find it easily, it is so bright, in the south at midnight, you can't mistake it, bright and red."
The event will be a feast for astronomers who, with a small telescope, will be able to pick out surface details on the planet such as its southern ice cap.
It will be a treat even with the naked eye but could provoke a crop of spurious UFO sightings.
Mars can be seen from anywhere on Earth but skywatchers at lower latitudes will have the best chance of a spectacular sighting when night falls.
Cloudy weather could obstruct the view but the planet has been particularly bright since July and will continue to be unusually visible for the next few weeks.
Shooting for Mars
The close encounter is a consequence of the orbits the Earth and Mars take around the Sun.
Best observing is between 10pm and 2am on August 26, 27 and 28
Earth has a more-or-less circular orbit while Mars takes a more elliptical path around the star.
This means Mars passes closer to Earth than usual at various times.
Calculations suggest that the last time they were this close together was when Neanderthals roamed the planet, on September 12, 57,617 BC.
Other significant encounters happened during the month of August in 1924, 1845 and 1766.
Space agencies have taken advantage of this year's celestial event to shoot probes at Mars.
Four space craft are on route to the Red Planet - two Nasa missions, Europe's Mars Express and a Japanese orbiter.
Mars Express, which was launched in June, has almost reached its halfway point.
It has flown about 24 million km and has some 32 million km left to travel.