The Structure of Sunspot Penumbras. I. Observations.

Abstract

In continuation of Project Stratoscope, the 12-inch solar telescope first flown in 1957 has again been flown to an altitude of 80000 feet during four unmanned balloon flights in 1959. The main new feature of these flights was the addition of television, telemetry, and channels which enabled the airborne telescope to be operated by remote control from a ground station. As a result, high-definition time sequences of sunspots were obtained. The penumbra is resolved into a complex array of predominantly radial bright filaments. These filaments are long, narrow structures having widths of 300 km or less and lengths of the order of 5000 km. Their lifetime is roughly five times that of the granules.