With exactly one month left before New England's last total eclipse of the century, two teams of Harvard astronomers are busily preparing their instruments.

A 25-foot tall Acrobec rocke? equipped with special ultra-violet light cameras, designed in part at the Harvard College Observalory, will arrive at NASA's missile range on Wallop's Island, Virginia next week. Edmond M. Reeves and William H. Parkinson, lecturers on Astronomy, are participating in the joint Canadian-British American rocket project that will observe the sun's chromosphere-a thin, outer layer of the sun that is distinguishable only during an eclipsc.

A second team of astronomers, headed by Donald H. Menzel, Paine Professor of Practical Astronomy and former director of the Harvard College Observatory, leaves today for Miahautlan, Mexico, where they will set up a temporary ground-based observatory for the March 7 eclipsc.

Sunny Mexico

The eclipse's deep shadow, called the umbra, will pass only over Southern Mexico, the Southeast U. S., Nantucket Island, Nova Scotia and Newfoundland. But, because the weather is likely to be best in Mexico, Menzel's group, as well as thousands of other observers, will set up camp there.

During the 3 minutes of the eclipse's totality, Jay M. Pasachoff 63, research associate in Astrophysics, will photograph the spectrum of the sun's corona-the shifting white halo of ionized gases that extends millions of miles from the sun's surface. These visible light spectra will provide a detailed picture of the chemical and physical events in the corna.

Winfield W. Salisbury, lecturer inAstronomy, will also study how the corona's light waves are oriented or polarized. The corona's polarization can reveal how the sun's magnetic field changes through space.

Pasachoff plans to report on the expedition for National Geographic, one of the group's sponsors.

While the Mexican expedition will make its most important observations in 3 minutes, the Aerobee rocket project will have only 3 seconds to photograph the chromosphere before the moon covers up that narrow layer.

The rocket will have to lift off within a specific five or ten second period known as the "launch window," rise to an altitude of 94 miles, and fall into the eclipse's shadow at a specific point. "Either it goes during that launch window or we pack it up and go home and wait for the next eclipse," said Edmund Reeves, shortly after supervising the hook-up of the 120-pound instrument package with the rocket at Goddard Space Flight Center in Maryland.

Even during an eclipse, the chromosphere's strong ultra-violet light emissions are blocked out by the earth's atmosphere. Thus a rocket or satellite is needed for studying this region.

The one previous attempt to do this-a French rocket launched from Brazil-was only a partial success.

"This is the first time a natural eclipse has passed over an established rocket range with all the established support facilities-the radar, weather prediction, telemetry, and ground crews-which you don't get when you do the job quick and dirty," Reeves said.

"We are compounding the problems of eclipse observation with the problems of ultra-violet rocketry, and just for spice, adding in the difficulties of a water recovery," he added.

"If you just sit down and rationally calculate the chances of success [10-20 per cent] you really wonder why you do it. But it is such a unique opportunity that we can't avoid trying for it," Reeves said.

The Harvard College Observatory's Orbiting Solar Observatory VI (OSO-VI) will take simultaneous ultra-violet observations of the sun's visible disc and corona during the rocket launch.

Since the March 7th eclipse is the last total eclipse to pass near a heavily populated area of the U.S. in this century, local amateur astronomers plan to congregate on Nantucket Island. The moon will cover all but 2 per cent of sun in Boston, but that 2 per cent of sunlight will be enough to drown out the sun's faint corona.

The Nantucket Chamber of Commerce expects the Island's winter guest houses and one hotel to be filled that weekend, while others may open temporarily. There is no public campground to house extra overnight visitors.

Executive Airlines and the Woods Hole, Martha's Vineyard, and Nantucket Steamship Authority may bolster their Nantucket schedules with extra trips to the Island on the eclipse date, but neither company has made a firm decision yet.

Nantucket eclipse-watchers may be disappointed: March 7 has a habit of being a very cloudy day on the Island.