Zurich to cease compiling sunspot series



By the end of this year, one of the oldest continuous series of astronomical data—the Zurich Relative Sunspot Numbers—will no longer be compiled. Other indexes of sunspot activity are under consideration as replacements.

J. O. Stenflo, the new director of the Swiss Federal Astronomical Observatory, where the Zurich numbers are compiled, has directed that the observatory discontinue this service by the end of 1980. An attempt to find a more accurate substitute for the somewhat subjective observations may have prompted the decision.