El Terror del Marte

It is hard to imagine what kind of cataclysm could cause Mars to appear as large in the sky as the full Moon, but it would probably mean the destruction of the Solar System as we know it and thus the end of all humankind.

That does not seem to stop the annoying e-mail circulating which says that Mars will be making its closest approach to Earth for 5,000 years (true, but this happened three years ago) and that Mars will look as large as the full Moon.

How could this possibly be true? Mars is about twice the size of the Moon, so a little elementary arithmetic reveals that if it looked the same size, it would be twice as far away; in other words, the Moon would be about half way between Earth and Mars. That’s wrong by a factor of about two hundred. This is the kind of order of magnitude error that you would be making if you thought I was 1200 feet tall, or that England and France are 4,000 miles apart. It’s not even vaguely plausible.

I think this is telling us that we have a worrying lack of basic astronomical literacy. Consider a circulated email which warned that the average temperature in England this summer would be 3,000 degrees Centigrade. This is wrong by approximately the same amount as the Mars meme, yet we wouldn’t give it a moment’s credence. It’s so obviously, hugely divergent from reality that we would assume immediately that it was a joke, or a typo.

It looks as if this is what happened with the Mars alert, as if you read the text carefully you can see that the confusion is caused by a rogue paragraph break:

The encounter will culminate on August 27th when Mars comes to within 34,649,589 miles 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.

The important bit is easy to miss: at a modest 75-power magnification. In other words, through a fairly decent telescope, Mars will look a similar size to that of the full Moon seen with the naked eye.

But this is stupid! Through a telescope, anything could look as big as anything else! You could say that at a modest 1,000-power magnification, an ant will look as large as a human being to the naked eye. That’s what a telescope is for. It magnifies things.

The circulation of this rubbish has become an annual event and wastes an awful lot of people’s time and inbox space, and the reason I mention it is that I see it has now been translated into Spanish - omitting, of course, the crucial qualifier.

Desmienten rumores sobre acercamiento de Marte a la Tierra (El Universal)

Rumors denied about Mars’ approach to Earth

(quoting from the e-mail)

El encuentro terminará el 27 de agosto, cuando Marte este a 55.439.342 Km de la Tierra. Entonces, junto con la Luna será el objeto más brillante en el cielo nocturno.

The encounter will end on 27th August, when Mars will be 55,439,342km from Earth [true]. At that time it will be, together with the Moon, the brightest object in the night sky.

A simple vista Marte parecerá tan grande como la Luna llena y será fácil de ver.

To the naked eye Mars will appear as large as the full Moon and will be easy to see. [no kidding]

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