New York.– An email promising a "Mars spectacular" on August 27 has astronomers seeing red, as scientists try to counter a seemingly unending Mars hoax. The anonymous message from an unknown part of the globe says that the red planet " … will look as large as the full moon" in the night sky, and that "no one alive today will ever see this again."

According to National Geographic, the claim has been bombarding people's inboxes worldwide every summer for five years. Today the Mars hoax has grown into a kind of cyber legend –one that astronomers are still struggling to debunk.

"The possibility of seeing Mars as large as the moon strikes the imagination," said Marc Jobin, staff astronomer at the Montréal Planetarium in Quebec. "The sad reality is that a lot of people have little comprehension of astronomy and are unable to call the hoax."

In fact, there is a thread of truth that inspired the prank several years ago. Planets are not on perfectly circular orbits, and during their elliptical paths around the sun, planets can vary in their exact distances to each other over time.

For example, Mars's orbit means that its distance from Earth can range from 34.6 million miles (55.7 million kilometers) to almost 250 million miles (401.3 million kilometers).

On August 27, 2003, Mars made a historically tight approach to Earth, coming about 34.7 million miles (56 million kilometers) away. Such a near pass hadn't happened in nearly 60,000 years, and it won't happen again until August 28, 2287.