302 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
the various points in the grid scan different strips across the sun. In 
this way a picture of the sun is built up in the manner of a tele- 
vision picture in a period of about half an hour (fig. 1). All 64 
paraboloids are turned on equatorial axes to continue pointing at the 
sun during this time. These radioheliograms may be compared 
with the well-known optical spectroheliograms taken in Ha light. 
The optical spectroheliograms give a comprehensive picture of the 
chromosphere, with its prominences, flares, and plages. The radio- 
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Figure 1.—Radioheliogram of the sun at 21 cm. The contour brightness unit is 0.93 x 
105 °K. (Diagram courtesy of Dr. W. N. Christiansen, CSIRO Division of Radio- 
physics, Sydney, Australia.) 
heliograms give an indication of the brightness distribution at a 
height of approximately 50,000 km. They show a close, but not per- 
fect correspondence with the chromospheric plages and sunspots. 
Similar instruments have now been put into operation at 1.8 m. and 
3.2 cm. at Meudon, France; 10 cm. at Stanford University; and 88 
em. at the Department of Terrestrial Magnetism of the Carnegie 
Institution of Washington. 
TRANSIENT RADIO BURSTS FROM THE SUN 
The discovery of intense transient radio bursts from the sun was 
made accidentally in England during the air battles of World War II. 
In February 1942, radar operators, watching the skies for enemy 
aircraft, noticed an unusual form of interference. It was at first 
