When will I see you again?

Natural History, Dec, 2004 by Peter Brown

On December 7, as Joe Rao reports in this issue (see "The Sky in December/January)," page 58), the Moon passes in front of the planet Jupiter, a relatively rare kind of eclipse known as an occultation. The event brings to mind a star date the author kept several years ago.

Driving north in the dark on the thruway, I think about the e-mail alert I got this afternoon from IOTA, the International Occultation Timing Association: "Naked-eye eclipse of bright star. ... Astronomers need your camcorder records for lunar and solar (Earth climate) studies." It's short notice: the last-quarter Moon is passing in front of the star Aldebaran tonight. But one point in the message caught my eye. Amateurs, it noted, can contribute to the basic science of global warming by timing the event. Whoa!

Against the drone of the traffic, my mind rehearses the steps in IOTA's logic. The trend toward global warming is clear, but there's plenty of debate about its causes. Could the problem be, say, too much Sun--a hundred-year hiccup in the solar output--instead of too many greenhouse gases from the twin trailer trucks around me?

But how do you detect changes in the Sun's output? One way is to measure changes in the size and shape of the Sun, best done when the Moon crosses the Sun during a total solar eclipse. According to IOTA, that's where I come in. The biggest source of error about the size and shape of the Sun is imprecise knowledge about the size and shape of the Moon. If I--and hundreds like me--can pinpoint our positions, and can time exactly when Aldebaran disappears and then reappears from behind the Moon, we can help astronomers determine the precise shape of the Moon. So I'm on my way to my house in rural upstate New York, to do my bit for science.

In my rush to get there, though, I've forgotten my watch. But I do remember that IOTA's alert mentioned something about using local TV broadcasts to fix the timing. Commercial radio, I figure, will do just as well, so I hatch my scheme: I'll bring a radio out into my yard, and sync the astronomical events with whatever I hear. After the occultation is over, I'll call the radio station to calibrate my times with the songs they've just broadcast. It seems like a plan.

I dash into the house for my toys: radio, lawn chair, paper and pencil, binoculars, a can of beer. Making fundamental contributions to astronomy and climatology might as well be comfortable. A lone bright star is about a third of the Moon's diameter away from the brilliant half Moon. The air is cool, and desert-clear. I crack the beer and turn on the radio.

The idea is to find some station that can give me sharp and unambiguous reference points that I can later describe to the station DJ. I tune in Z93 in New Paltz, but they're playing a long rock ballad: too hard to tell one moment from the next. The star is closing in fast, about a sixth of a lunar diameter from contact. I surf the dial for another station.

I pick up Jukebox Radio, out of Fort Lee, New Jersey. Bob Bober, the DJ, says he'll do ten in a row. He starts off with the 1963 Beach Boys hit "Surfer Girl," and I know I'm on familiar turf. But the Moon's bright limb is overwhelming the star. "Surfer Girl" fades out and song number two fades in, "Ready to Take a Chance on You Again." I notice the jewel-like Pleiades just above the Moon; Aldebaran, though, is lost in the Moon's glare. My chance to fix the instant of the star's disappearance is lost. Success now depends on spotting Aldebaran the moment it reappears from behind the dark lunar limb.

Jukebox Radio plays number three: "When Will I See You Again?" I realize I have no idea how to answer the question. Worse, my station is breaking up. I fiddle with the antenna, make notes in the dark, try to hold the binoculars steady on the edge of the Moon. It's a struggle. Bob Bober plays "Any Day Now." I look down briefly to scribble something in the darkness. When I look back, there's the star! I've missed its "emersion" by three, maybe five, seconds.

Bober gives the weather: Saturday will be clear, high seventy-five. I get up and stretch. The Moon and the star are drifting apart now. I hear the crickets, notice the fireflies for the first time. I walk up the road, drained from the excitement. Dawn is coming: another celestial rendezvous. This one I'll pass.

PETER BROWN is the editor of Natural History. Since his abortive attempt to time this occultation, he has learned how a videotape of the event, dubbed with the calibrated audio signal of a broadcast, can time such events to within several hundredths of a second.