Shallow Thoughts

Akkana's Musings on Open Source, Science, and Nature.

Fri, 28 Oct 2005

A Value of "Close" With Which I was Previously Unfamiliar

A very strange article in today's SF Chronicle describes "Mysterious, bright lights in the night sky Wednesday that alarmed or bemused scores of Bay area residents".

It atributes to Andrew Fraknoi, chairman of the Foothill College astronomy department and media hound (it doesn't say that second part), information that "the lights were probably Mars and Venus, two planets that currently appear close together and will probably remain brilliant for another week or two until their orbits begin moving them away from the Earth again."

Aside from the "probably" (I was under the impression that the basic orbits of the major planets were fairly well understood, and that it's fairly rare that a planet suddenly deviates from its regular orbit in a visible way), I found this curious because Venus is currently in the early evening sky -- since its orbit lies inside that of the Earth, it can never appear to move very far from the Sun -- while Mars, a week before opposition, is rising in the early evening and overhead at roughly midnight.

Just to be sure, I checked with XEphem. The angular distance between Mars and Venus is current 146°. They're almost at opposite ends of the sky. This is a definition of "close" with which I was previously unfamiliar.

I don't know if Fraknoi really said this, or if he was simply misquoted by the reporter, David Perlman, the Chronicle's Science Editor. If so, the misquote is quite pervasive -- he repeats several times throughout the article Fraknoi's assurance that the lights (shown in a photograph accompanying the article, indeed close together though we aren't told anything about the lens used to take the photo) must be Venus and Mars.

Other giggle-inducing quotes from the article:

No one except astronomers could offer an explanation.
Well, gosh, you certainly wouldn't want to listen to those egghead astronomers about a question involving lights in the sky.

(Well, okay, in this case you shouldn't listen to them, because the Mars/Venus explanation obviously doesn't fit the observations.)

According to Fraknoi, Mars now far outshines even the brightest of all the stars in the sky, and when skies are clear, the fourth planet from the sun could look even bigger than normal.
Mars at opposition is certainly brighter than any star (except the Sun, of course). It currently shines with a magnitude of about -2.2 (a smaller number means a brighter object; the brightest star, Sirius, is magnitude -1.4. Venus, at the moment, is much brighter than either one at -4.2, as is usual since it's larger, closer, and more reflective than Mars. That might have been worth mentioning.

I can't figure out whether "even bigger than normal" is supposed to refer to size or brightness. Mars is normally a tiny object as viewed from Earth, too small to see much detail except for a few months around opposition every couple of years. Indeed it is much bigger than normal right now (and a lovely sight in a telescope!), as well as brighter; but "even bigger" seems like an odd phrasing for something normally so small.

But since Mars' size isn't visible except in a telescope, Dave thinks "bigger" here was meant to refer to brightness: the misconception that brighter objects look bigger. I shouldn't make fun of this: the great astronomer Tycho Brahe, in the 1500's, was convinced that stars had angular size instead of being point sources. He thought brighter stars appeared bigger, and based his geocentric solar system model on that. That view wasn't disproved until Galileo invented the telescope. It's a common misconception even today, but I'd hate to think the Chronicle's science editor was encouraging it, so I'll stick to the assumption that he really meant size and that the "even" was just an odd journalistic embellishment.

So what were the mysterious lights? I don't know. I didn't see them, and the article doesn't give enough detail to make a good guess. But the photo looks a lot like airplanes or helicopters; at least one of the lights has a couple of smaller lights to either side, usually a dead giveaway for an aircraft.

Update the following day: I wasn't the only one to complain about this article, and the Chron published a paragraph in the Corrections section this morning clarifying that Venus is nowhere near Mars and could not have been related to the lights people reported.

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