The date alone may be unlucky for some, but it could prove to be a fatal encounter for the people of Planet Earth when the 350 metre wide asteriod passes by.

Apophis was originally given the less apocalyptic name of 2004-MN when it was first spotted by astronomers four years ago.

But since then its trajectory has been charted, and perhaps more fittingly it has been re-named after the enemy of the ancient Egyptian sun god Ra, a serpent that dwells in the eternal darkness of the underworld.

And like a snake, Apophis has the potential to strike.

Calculations indicate that while there is only a slim chance it could enter the Earth's atmosphere on that given day, there's also the possibility that it could return seven years later.

The reason is that Apophis may instead hit a so-called "gravitational keyhole", no more than about 600 meters across, which could set up a future impact in 2036.

As fate would have it, that would also fall on April 13.

Experts consider Apophis serious enough that the Planetary Society decided to award $50,000 in prize money to whoever who could design a space probe that would put a tracking device on or near the asteroid.

Even then, however, the possibility of a collision, particularly in 2036, can't be ruled out.

Jon Giorgini, a senior analyst at Nasa's Jet Propulsion Laboratory's Solar System Dynamics group, and a member of the radar team that observed Apophis, said: "The future for Apophis on Friday, April 13 of 2029 includes an approach to Earth no closer than 29,470 km (18,300 miles, or 5.6 Earth radii from the center, or 4.6 Earth-radii from the surface) over the mid-Atlantic, appearing to the naked eye as a moderately bright point of light moving rapidly across the sky.

"Depending on its mechanical nature, it could experience shape or spin-state alteration due to tidal forces caused by Earth's gravity field."

But he added: "The problem of computing an impact probability for Apophis is that the true 2029 "keyhole" leading to a 2036 impact is not known in the absence of knowledge of the complete dynamics.

"The problem is acute enough for Apophis that, if impact hasn't been previously excluded, and there hasn't been a thorough physical characterization, it can't be known for certain it will impact until during or after the 2029 encounter, even if a spacecraft is accompanying Apophis and providing position measurements good to two meters.

"That is, the keyhole could be determined only retrospectively, after passage through it."

And what if it does come crashing down to Earth?

Nasa has previously estimated the energy delivered by Apophis would be the equivalent of 1,480 megatons of TNT.

That's the twice the level of every single nuclear test carried out since the invention of the atom bomb, all combined in a single explosion.

By comparison, the 1883 eruption of the Krakatoa volcano in the Pacific Ocean was roughly 200 megatons.

That was enough to lower the average global temperatures by 1.2 degrees Celsius for a year, and cause chaos in weather patterns for the next five, as well as increase acid rain.

Optical effects caused by Krakatoa blowing itself apart were seen as far away as Oslofjord in Norway, and spectacular sunsets caused by the enormous cloud of dust ejected into the atmosphere were recorded world-wide.

When Apophis eventually does reach us, many will be crossing their fingers.

It will follow a path across southern Russia, the north Pacific, relatively close to the coastlines of California and Mexico, then between Nicaragua and Costa Rica, crossing northern Colombia and Venezuela, ending in the Atlantic, just before reaching Africa.

Computer simulations project casualties in the region of 10 million were it to come down in Central America, and if it hits the sea it would create an equally devastating tsunami.

But we do have one thing going in our favour, at least.

April 13, 2036 falls on a Sunday, so luck may just be on our side.

And if not, at least we won't have to turn in for work on Monday morning.