Rock and roll: Asteroid swings by Earth

Space Situational Awareness - Near Earth Objects Asteroid approaching Earth.

An asteroid nicknamed after a maligned dog and with the potential to cause catastrophic damage will pass within 40,000km of Earth today and scientists are ruling out any chance of it colliding with the planet in the foreseeable future.

The asteroid, officially called 2014RC and nicknamed "Pitbull", was first spotted on August 31.

Nasa says it will be a close shave but there is no risk and at its closest approach - expected between 6am and 7am today - the asteroid should be at its brightest over New Zealand.

Stardome Observatory astronomer Dr Grant Christie said casual observers wanting to catch a glimpse of the giant rock, which is 20m across, would probably be "searching for a cork in the ocean".

He said experienced star gazers would need a telescope with at least a 35cm to 40cm aperture to see it comfortably.

"But even at its brightest you would need a decent-sized telescope like the device at One Tree Hill," he said.

Dr Christie said that after the asteroid encounters the Earth's gravitational field, it would probably get a kick, causing a slingshot effect.

"I am not sure what will happen to the dynamics after that."

He said scientists would be able to calculate its precise position in space and by using that data, others would be able to calculate its orbit.

National Geographic's website said astronomers had ruled out any chance of Pitbull colliding with Earth for the foreseeable future. James Ihaka