Return of the Mars Hoax

For the sixth year in a row, a message about the Red Planet is popping up

in email boxes around the world. It instructs readers to go outside after

dark on August 27th and behold the sky. "Mars will look as large as the full

moon," it says. "No one alive today will ever see this again."

Don't believe it.

Here's what will really happen if you go

outside after dark on August 27th. Nothing.

Mars won't be there. On that date, the red

planet will be nearly 250 million km away

from Earth and completely absent from

the evening sky.

Right: Only in Photoshop does Mars appear

as large as a full Moon.

The Mars Hoax got its start in 2003 when Earth and Mars really did have a

close encounter. On Aug. 27th of that year, Mars was only 56 million km

away, a 60,000-year record for martian close approaches to Earth. Someone

sent an email alerting friends to the event. The message contained some

misunderstandings and omissions—but what email doesn't? A piece of

advanced technology called the "forward button" did the rest.

Tolerant readers may say that the Mars Hoax is not really a hoax, because
it is not an intentional trick. The composer probably believed everything he
or she wrote in the message. If that's true, a better name might be the "Mars
Misunderstanding" or maybe the "Confusing-Email-About-Mars-You-Should-
Delete-and-Not-Forward-to-Anyone-Except-Your-In-Laws."

Another aspect of the Mars Hoax: It says Mars will look as large as the full

Moon if you magnify it 75x using a backyard telescope. The italicized text

is usually omitted from verbal and written summaries of the Hoax. (For

example, see the beginning of this story.) Does this fine print make the

Mars Hoax true? After all, if you magnify the tiny disk of Mars 75x, it does

subtend an angle about the same as the Moon.

No. Even with magnification, Mars does not look the same as a full Moon.

This has more to do with the mysterious inner workings of the human brain

than cold, hard physics. Looking at Mars magnified 75x through a slender

black tube (the eyepiece of a telescope) and looking at the full Moon shining

unfettered in the open sky are two very different experiences.

Above: Mars in August 2003 during a 60,000-year record close approach.

Even then, the planet resembled a bright star, not a full Moon. Photo credit:

John Nemy & Carol Legate of Whistler, B.C.

A good reference is the Moon Illusion. Moons on the horizon look huge; Moons

directly overhead look smaller. In both cases, it is the same Moon, but the human

mind perceives the size of the Moon differently depending on its surroundings.

Likewise, your perception of Mars is affected by the planet's surroundings. Locate

the planet at the end of a little dark tunnel, and it is going to look tiny regardless

of magnification.

Bummer!

To see Mars as big as a full Moon, you'll need a rocketship, and that may take

some time. Meanwhile, beware the Mars Hoax.

source:NASA