Approaching Mars

Posted by jns on 22 August 2007

Before I even get that ridiculous e-mail about how Mars will soon look as big as the moon because of a close approach by the Earth, here’s a note from NASA:

August 21, 2007: By the time you finish reading this sentence, you’ll be 25 miles closer to the planet Mars.

Earth and Mars are converging, and right now the distance between the two planets is shrinking at a rate of 22,000 mph–or about 25 miles per sentence. Ultimately, this will lead to a close approach in late December 2007 when Mars will outshine every star in the night sky. Of a similar encounter in the 19th century, astronomer Percival Lowell wrote the following: “[Mars] blazes forth against the dark background of space with a splendor that outshines Sirius and rivals the giant Jupiter himself.”

Contrary to rumor, though, Mars is never going to outshine the Moon.

There is an email circulating the internet—called the “Mars Hoax” or the “Two Moons email”—claiming that Mars will soon swell as large as the full Moon, and the two will hang together side by side on the night of Aug. 27th. “Mars will be spectacular,” it states. “No one alive today will ever see this again.”

No one will see it, because it won’t happen.

It is true that Earth and Mars are converging–you’re now 300 miles closer–but even at closest approach the two planets are separated by a gulf of tens of millions of miles. From such a distance, Mars looks like a star, an intense yet tiny pinprick of light, never a full Moon.

[excerpt from Dr. Tony Phillips, "Hurtling Towards Mars", Science @ NASA, 21 August 2007.]

I rather like the poetry of their special-purpose units for velocity: miles / (sentence read).