WASHINGTON (AFP) - A mysterious meteor shower late Friday and early Saturday is captivating countless astronomers and amateur skywatchers with the promise of a falling-star show unlike any ever before seen.

The first appearance of a meteor shower known as Camelopardalids could start for North American viewers at early as 10:30 pm Friday, astronomers say.

It should be visible in the United States and Canada, anywhere with a cloudless night sky. Unfortunately, the rest of the world is likely to miss out.

The peak is expected between 3 and 4 am (0700-0800 GMT), according to Bill Cooke, head of NASA's Meteoroid Environment Office in Huntsville, Alabama.

"However, I would recommend folks get out a bit earlier, just to be safe," Cooke told AFP.

And what will it look like? Astronomers aren't exactly sure. They have never seen this one before.

"Meteor showers are like the weather. They are a little bit hard to predict," said Paul Wiegert, associate professor at University of Western Ontario.

This meteor show originates from the trail of dust behind a comet known as 209P/Linear, which gets tugged into Earth's orbit this year by the force of gravity from Jupiter.

Meteors are space rocks that burn up upon hitting the top of Earth's atmosphere, producing a bright flash of light that gives the appearance of a falling star.

"The predictions at this point are that we will see a few hundred meteors per hour," Wiegert told AFP.

"That means that you would see a few meteors per minute. So it is not a special-effects extravaganza, here, but it is in line with many of the strong annual meteor showers."

The annual Perseids meteor show that lasts for several days in August consists of shooting stars that barrel by at a pace of 241,000 kilometers per hour.

The Camelopardalids meteors will move comparatively slowly, traveling at around 58,000 kilometers per hour, Cooke said.

A key piece of this meteor show mystery lies in the ancient trail of dust behind the comet, which was produced centuries ago.

"The problem we are having is even though we can tell precisely when these particles are going to encounter Earth's orbit, we don't know how many of them there are," said Cooke. Right now the comet does not produce much debris.

"But we have no idea what it was doing 200 years ago, because it wasn't discovered until 2004," added Cooke.

The best way to take in a meteor show is to go outdoors, lay flat on your back and look skyward, said Cooke. No special equipment necessary.