26 January 1998
Our nearest star, the Sun, is currently becoming more active after one of its relatively quiet periods. Continuous observations from SOHO reveal a never-ending cauldron of activity. Indeed, the surface of our Sun resembles a quilt of highly variable bright patches, known as supergranulation. This apparent mottling pattern is caused by an underlying structure of convection cells in the body of the Sun where extremely hot gas rises to the surface, cools and sinks back down again.
The CDS observers have noted what appear to be brief, localised bright patches within these supergranular patterns. These flashes, now known as blinkers, are small explosions in the Suns atmosphere, each of them about the size of the Earth. Although these blinkers appear to be rather insignificant since they are small and emit only one millionth the energy of a solar flare, they are distributed over the entire Sun and are visible for several minutes. They seem to be the visible representation of a transient process which is basic to the way the solar atmosphere works.
The discovery of the blinkers may help to resolve two outstanding problems in solar physics. How does the Sun ejects a continuous stream of gas into space as the so-called solar wind? And how is its outer atmosphere (the corona) heated to over 1 million degrees when the surface is only 5,500 degrees C (10,000 degrees F)? The blinker explosions may well represent sites of plasma heating or/and particle acceleration which can explain these phenomena. (Plasma is a very hot gas composed of electrons and atomic nuclei.)
The general SOHO Web site is at
http://sohowww.nascom.nasa.gov/ (click on Gallery and CDS or LASCO)
CDS is able to study different layers of the Sun's rarefied atmosphere, ranging from the superhot corona to the lowest levels where supergranulation is seen. By measuring the invisible radiation emitted at extreme-ultraviolet wavelengths, Dr. Harrison's team is able to study the 'weather' - that is, temperature, gas flow patterns and density - of these regions.
The CDS investigation has unveiled a huge range of solar activity. In addition to the supergranulation and blinkers, jets of superhot gas and huge clouds - or prominences - can be seen. These prominences, which could swallow up dozens of Earth- sized planets, lift high into the solar atmosphere without actually separating from the Sun, although they can occasionally erupt into space.
SOHO was launched on December 2, 1995, and placed in orbit around the Sun at a position between the Earth and Sun on February 14, 1996. Scientific operations began in April 1996. Since then, RAL's CDS instrument has been used by 36 institutes from 12 countries and has carried out 50,000 observations. Almost 100 scientific papers based on CDS have been published or submitted for publication. The CDS operation is run from RAL.
Scientists from the University of Birmingham, under the leadership of Dr. George Simnett, helped to build another instrument on SOHO, the Large Angle Spectroscopic Coronagraph (LASCO).