«Looking?»
«Lasers,» I said, pointing to the low-key lights over the consoles. «Optical lasers. Superlamps shining out in the darkness of the void. Pump in a modest amount of electrical power, excite a few trillion atoms, and out comes a coherent, pencil-thin beam of light that can be seen for millions of miles.»
«Millions of miles aren’t light-years,» Rizzo muttered.
«We’re rapidly approaching the point where we’ll have lasers capable of lightyear ranges. I’m sure that some intelligent race somewhere in this galaxy has achieved the necessary technology to signal from star to star— by light beams.»
«Then how come we haven’t seen any?» Rizzo demanded.
«Perhaps we already have.»
«What?»
«We’ve observed all sorts of variable stars—Cepheids, RR Lyrae’s, T Tauri’s. We assume that what we see are stars, pulsating and changing brightness for reasons that are natural, but unexplainable to us. Now, suppose what we are really viewing are laser beams, signalling from planets that circle stars too faint to be seen from Earth?»
In spite of himself, Rizzo looked intrigued.
«It would be fairly simple to examine the spectra of such light sources and determine whether they’re natural stars or artificial laser beams.»
«Have you tried it?»
I nodded.
«And?»
I hesitated long enough to make him hold his breath, waiting for my answer. «No soap. Every variable star I’ve examined is a real star.»
He let out his breath in a long, disgusted puff. «Ahhh, you were kidding all along. I thought so.»
«Yes,» I said. «I suppose I was.»
Time dragged along in the weather dome. I had managed to smuggle a small portable telescope along with me, and tried to make observations whenever possible. But the weather was usually too poor. Rizzo, almost in desperation for something to do, started to build an electronic image-amplifier for me.
Our one link with the rest of the world was our weekly radio message from McMurdo. The times for the messages were randomly scrambled, so that the chances of their being intercepted or jammed were lessened. And we were ordered to maintain strict radio silence.
As the weeks sloughed on, we learned that one of our manned satellites had been boarded by the Reds at gunpoint. Our space-crews had put two Red automated spy-satellites out of commission. Shots had been exchanged on an ice-island in the Arctic. And six different nations were testing nuclear bombs.
We didn’t get any mail of course. Our letters would be waiting for us at McMurdo when we were relieved. I thought about Gloria and our two children quite a bit, and tried not to think about the blast and fallout patterns in the San Francisco area, where they were.
«My wife hounded me until I spent pretty nearly every damned cent I had on a shelter, under the house,» Rizzo told me. «Damned shelter is fancier than the house. She’s the social leader of the disaster set. If we don’t have a war, she’s gonna feel damned silly.»
I said nothing.
The weather cleared and steadied for a while (days and nights were indistinguishable during the long Antarctic winter) and I split my time evenly between monitoring the meteorological sensors and observing the stars. The snow had covered the dome completely, of course, but our «snorkel» burrowed through it and out into the air.
«This dome’s just like a submarine, only we’re submerged in snow instead of water,» Rizzo observed. «I just hope we don’t sink to the bottom.»
«The calculations show that we’ll be all right.»
He made a sour face. «Calculations proved that airplanes would never get off the ground.»
The storms closed in again, but by the time they cleared once more, Rizzo had completed the image-amplifier for me. Now, with the tiny telescope I had, I could see almost as far as a professional instrument would allow. I could even lie comfortably in my bunk, watch the amplifier’s viewscreen, and control the entire set-up remotely.
Then it happened.
At first it was simply a curiosity. An oddity.
I happened to be studying a Cepheid variable star—one of the huge, very bright stars that pulsate so regularly that you can set your watch by them. It had attracted my attention because it seemed to be unusually close for a Cepheid—only 700 lightyears away. The distance could be easily gauged by timing the star’s pulsations. [Astronomers have been able, since about 1910, to estimate the distances of Cepheid variable stars by timing their pulsations. The length of this type of star’s pulsation is a true measure of its intrinsic brightness. Comparing the star’s actual brightness to its apparent brightness, as seen from Earth, gives a good value for the star’s distance.]
I talked Rizzo into helping me set up a spectrometer. We scavenged shamelessly from the dome’s spare parts bin and finally produced an instrument that would break up the light of the star into its component wavelengths, and thereby tell us much about the star’s chemical composition and surface temperature.
At first I didn’t believe what I saw.
The star’s spectrum—a broad rainbow of colors—was crisscrossed with narrow dark lines. That was all right. They’re called absorption lines; the Sun has thousands of them in its spectrum. But one line—one— was an insolently bright emission line. All the laws of physics and chemistry said it couldn’t be there.
But it was.
We photographed the star dozens of times. We checked our instruments ceaselessly. I spent hours scanning the star’s «official» spectrum in the microspool reader. The bright emission line was not on the catalogue spectrum. There was nothing wrong with our instruments.
Yet the bright line showed up. It was real.
«I don’t understand it,» I admitted. «I’ve seen stars with bright emission spectra before, but a single bright line in an absorption spectrum! It’s unheard-of. One single wavelength … one particular type of atom at one precise energy-level … why? Why is it emitting energy when the other wavelengths aren’t?»
Rizzo was sitting on his bunk, puffing a cigaret. He blew a cloud of smoke at the low ceiling. «Maybe it’s one of those laser signals you were telling me about a couple weeks ago.»
I scowled at him. «Come on, now. I’m serious. This thing has me puzzled.»
«Now wait a minute … you’re the one who said radio astronomers were straining their ears for nothing. You’re the one who said we ought to be looking. So look!» He was enjoying his revenge.
I shook my head, and turned back to the meteorological equipment.
But Rizzo wouldn’t let up. «Suppose there’s an intelligent race living on a planet near a Cepheid variable star. They figure that any other intelligent creatures would have astronomers who’d be curious about their star, right? So they send out a laser signal that matches the star’s pulsations. When you look at the star, you see their signal. What’s more logical?»
«All right,» I groused. «You’ve had your joke …»
«Tell you what,» he insisted. «Let’s put that one wavelength into an oscilloscope and see if a definite signal comes out. Maybe it’ll spell out ‘Take me to your leader’ or something.»
I ignored him and turned my attention to Army business. The meteorological equipment was functioning perfectly, but our orders read that one of us had to check it every twelve hours. So I checked and tried to keep my eyes from wandering as Rizzo tinkered with a photocell and oscilloscope.
«There we are,» he said, at length. «Now let’s see what they’re telling us.»
In spite of myself I looked up at the face of the oscilloscope. A steady, gradually sloping greenish line was traced across the screen.