Mars WILL NOT Appear As Large As The Full Moon

Mars WILL NOT Appear As Large As The Full Moon

via One-Minute Astronomer de admin em 28/07/09

Yes, the "great Mars hoax" email is back. Since 2003, the email seems to make rounds at least once a year, claiming Mars will appear as large as the full moon in late August.

Sorry to say, that's not going to happen.

The email got started in 2003. In August of that year, Mars came within 56 million km of Earth, the closest approach in 60,000 years. It was an impressive event. But even then, when the planet was a breathtaking magnitude -2.9, Mars measured about 25 arc-seconds across. That's about 75x smaller than the full moon.

As it turns out, the original email about the close approach of Mars correctly mentioned this fact. It said:

"The encounter will culminate on August 27th when Mars comes to within 34,649,589 miles (55,763,108 km) of Earth and will be (next to the moon) the brightest object in the night sky. It will attain a magnitude of -2.9 and will appear 25.11 arc seconds wide. At a modest 75-power magnification Mars will look as large as the full moon to the naked eye."

This was true… in a telescope at 75x, Mars would subtend an angle of about 1/2 degree, the same as the full moon.

I suspect when the email was forwarded, eventually the words "At a modest 75-power magnification…" were left out. That's when the confusion began. And on some versions of the email, the year in which the event took place was left out, which is why the email seems to get most traffic just before August.

To be fair, I think the email going around today isn't really a hoax, but a misunderstanding. But if it appears in your inbox, remember, its claims are completely bogus, although they was founded in fact back in 2003.

Right now, Mars is about 250 million kilometers away and appears almost 5x smaller than it was in August 2003. At a puny 6 arc-seconds across, it's putting on a middling show in the early morning sky. You can see it between Venus and the Pleiades, right above Orion. Here's an image of what you'll see in late July when you face east at sunrise.

Mars and Venus in the pre-dawn sky in late July 2009

Because Mars is so far away, you won't see much surface detail, even in a powerful telescope.

The best planet for viewing this month is Jupiter, visible in the southeast sky after 10 p.m. local time. It's the brightest object in that part of the sky (except for the moon).