An airborne eye on the cosmos

''Here we are deep in the heart of Taurus,'' puns Neil J. Evans II, an astronomer from the University of Texas, laconically. As he jokes, he keeps an eagle eye on the column of numbers which march down the green computer screen in front of him.

These figures represent measurements of an obscure object in the constellation Taurus which he hopes will turn out to be a star in the throes of birth.

Dr. Evans is observing these data from aboard a Lockheed Starlifter, especially modified to carry a 36-inch telescope. The aging military jet transport, known as the Gerald P. Kuiper Airborne Observatory, was converted in 1975 by the National Aeronautics and Space Administration (NASA). Since then, the plane, which makes 60 flights a year, has carved out a unique astronomical niche for itself.

Mission director Carl Gillespie checks off some of the high points: discovery of the rings around Uranus; demonstration that the giant gas planets - Jupiter, Saturn, and Neptune - are giving off more energy than they receive from the sun; discovery that the atmosphere of Venus contains concentrated droplets of sulfuric acid; determination that a certain class of galaxies is 100 times brighter than is our own.

By flying into the upper reaches of the atmosphere, the observatory enables astronomers to study features obscured at lower elevations. In particular, it provides a window on the cooler objects in the universe: those whose temperatures are less than 3,000 degrees C. These shine brightest in the infrared, that portion of the electromagnetic spectrum which is sandwiched between visible light and microwaves and absorbed by water vapor.

Infrared sources include interstellar dust clouds and planetary systems. Stars at both the beginning and end of their lives glow brightest at infrared wavelengths. And some of the most distant objects in the universe - remote galaxies and mysterious quasars - are receding at such high velocities that their light is shifted into the infrared.

On this particular November flight, there are no great discoveries. Instead, the flight was illustrative of a less dramatic but far more common side of science that requires much painstaking and unglamorous labor. Here's a rundown:

At 6 in the evening, Dr. Evans is in high spirits as the Kuiper thunders down the runway and into the fading twilight over San Francisco Bay. The sensitive detector that he will be using, developed by his University of Texas colleague Paul Harvey, has checked out perfectly.

Tonight our course takes us out into the Pacific, back across California, north over Oregon, Washington, Idaho, and Montana almost to the Canadian border, then south to Nevada, zigzagging over Ogden and Salt Lake, Utah, and Pocatello, Idaho, then back to San Francisco.

While the plane climbs to cruising altitude (39,000 to 41,000 feet), where it will be above 99 percent of the atmosphere's water vapor, the crew pays close attention to monitors and gauges. NASA crewman Don Oishi readies the telescope, which sits in an airtight compartment just behind the cockpit. This is isolated from the rest of the plane by a series of shock absorbers. Dr. Harvey begins calibrating the detector.

The telescope swings up and down through 40 degrees but moves backward and forward only 4 degrees. This means that most of the pointing must be done by steering the aircraft. Dr. Evans supplied NASA with a list of objects he wished to observe and space-agency navigators worked out a complicated flight plan.

''Pointing an airborne telescope like this is quite a bit more complicated than it is on an ordinary telescope,'' explains Allan Meyer dryly. His sole job is acquiring targets for the scientists. He does this by using photographs of the sky prepared in advance. Three television cameras are used to help point the telescope.

''Generally, the objects the scientists want to look at are too faint to be seen,'' Mr. Meyer elaborates. ''So we pick out a visible star in the area to serve as a guide star. The telescope can be offset by an amount corresponding to the distance of the object from the star.''

Above his head is a large television monitor which displays the view from one of the telescope cameras. Working from astronomical plates that show the pattern of visible stars in the region of the object, Meyer uses a joy stick to guide the telescope to the proper guide star.

Now Paul Harvey takes over with an air reminiscent of a symphony conductor. Instead of a baton, however, the astronomer clutches a small aluminum box at the end of a cable. On it are four buttons which move the telescope. He uses this to keep the guide star in focus when taking measurements at various points around the object of interest.

The evening's research starts badly. As the telescope slues in on the first target, suddenly the instruments begin registering noise. Then, as abruptly as it started, the mysterious noise vanishes.

As the infrared measurements of the first object begin coming, they look good. But soon the signal seems to vanish.

Most of the objects Evans is investigating were found with a radiotelescope. These radio observations provided evidence that they are violently ejecting dust and gas - a sign of a newly formed star. The infrared measurements will tell Evans how hot the objects are. And this will help him determine what stage in their evolution the dust-veiled stars have reached.

''A couple of years ago,'' the astronomer explains, ''everybody's picture of star formation was that dust and gas collapse to form the star. But no one has yet seen evidence of collapsing dust. Instead, people are seeing matter coming out, being ejected, even at very early stages in a star's life.''

Evans's frustration builds, as several of the targets fail to show significant infrared radiation. In addition, a strong tailwind has unexpectedly reduced observing time on a number of targets.

It is not until the end of the flight that Evans finally hits pay dirt. The columns of numbers scrolling on the computer screen indicate something interesting. Excitedly, the scientists begin taking readings at a number of points around the object. Its hot core is located. They map the temperatures of dust fans radiating out from it at several points.

''It started off pretty bad but ended on a real high note,'' Evans summarizes , as the plane drops rapidly toward a landing. It will be more than a month until he can analyze the computer tapes of the measurements.

Gillespie, who has been with the airborne observing program since its inception, dreams of one day mounting a larger telescope on a Boeing 747. He even has a picture of it on his office wall. But he admits it's not very likely. ''The agency isn't giving much emphasis to aircraft these days,'' he sighs.

NASA's plans for infrared astronomy are now focusing on space. The infrared astronomical satellite (IRAS) has proved successful. In the short run, this will probably increase the demand for the Kuiper, because its telescope can focus in on smaller details than can the satellite. But in the long run the space agency has its eyes on an infrared observatory to fit in the bay of the space shuttle.