East-West Baseline

Abstract

Long-baseline interferometry makes the world its radiotelescope. Combining signals from two observatories spaced far apart, astronomers can distinguish small objects as well as they could with a single telescope as big as the distance between the two (SN: 10/13/67, p. 370). To take full advantage of the technique, the telescopes should be as far apart as possible. This requirement even overrides political differences and is providing one of the smoothest examples of Soviet-American cooperation, with joint observations by the National Radio Astronomy Observatory at Green Bank, W. Va., and the Crimean Astrophysical Observatory at Simferopol in the U.S.S.R. The project, which involves reciprocal visits by personnel and use of American equipment in the Crimea, was planned by scientists who knew each other and were able to get the approval of their respective governments. Radio astronomers have practiced interferometry for years, but until recently telescopes used for the purpose had to be connected by a cable or microwave link. This limited distances between telescopes to a few tens of miles at most. In the last few years improvements in highly accurate atomic clocks have made it possible to combine recorded signals by computer after the fact rather than having to combine live signals at the time of observation. With this technique the distance between telescopes-the interferometry baseline -can be the diameter of the earth. That is the longest distance (until there are radio telescopes on the moon) between two telescopes that can see the same object at the same time. The United States and the Soviet Union are on opposite sides of the world, and the Green Bank-Crimea cooperation is the longest baseline interferometric observation yet attempted, a distance of about 6,000 miles. Green Bank has done intercon:~~~~~~~~~~~~~~~~~~~~~. .. .. . . . . ..