Mars passes closer to the Earth this week than it has at any time in almost 60,000 years.
The last time humans looked up and saw such a dazzling vision of the Red Planet they were living in caves and wearing animal skins.
The precise time of closest approach will be 9.51am on Wednesday, when a mere 34,646,418 miles will separate the Earth and Mars – 145 times the distance to the Moon.
As it is daytime, the moment will be missed in Ireland. But during the night before or after, Mars will only be about 2,000 miles further away and just as great a spectacle.
Already it is impossible to miss the planet, a fiery yellow-orange disc in the south-eastern sky that far outshines the brightest star, Sirius.
The event is a big occasion for amateur astronomers, who will have to wait 284 years for Mars to come as near again.
Mars-watching is very much an activity for nightbirds. At 11pm the planet will be just above the rooftops and shrouded by the murky layers of atmosphere that hug the horizon.
To see Mars clearly it is necessary to stay up until 1am, when the planet will be sufficiently high in the sky.
The reason Mars is so close to the Earth this year has to do with the planets’ orbits.
Earth and Mars are like two runners going round a racetrack at different speeds.
As it circles the Sun, Mars is on average about one and a half times farther away than the Earth. It takes 687 days to complete one orbit, compared with the Earth’s 365.
Roughly every 26 months, Earth overtakes Mars on the inside, causing a close encounter between the two planets as it passes. If the planets’ orbits were circles, the distance between them would be the same every time this occurs. But their orbits are actually oval-shaped, and Mars in particular follows a very non-circular path.
As a result the distance between Earth and Mars at their closest approach can vary between 35 million and 63 million miles.