290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
satellites that can carry several thousand pounds of scientific equip- 
ment into orbits hundreds of miles above the surface of the earth. 
It now appears certain that as a result of the developments in rocket 
technology, astronomy has entered a new era which promises to be 
the most exciting in its history. As Otto Struve so aptly put it in a 
message to the Tenth General Assembly of the International Astro- 
nomical Union recently held in Moscow: “Because of this event [the 
successful launching of the first sputnik] the year 1957 will be re- 
membered in the history of astronomical exploration as the year 1492 
is remembered in the history of geographical exploration.” 
The way is now open for attack on some of the most fundamental 
problems of astrophysics. Furthermore, the possibility of creating 
also artificial planets and artificial satellites of planets other than the 
earth has very important implications for celestial mechanics. Time 
does not permit the listing of the dozens of fresh and exciting satellite 
experiments that can be visualized by any competent astronomer. In- 
stead, since the Arthur Lectures are devoted to the sun, I shall confine 
my attention to this, the most important star in the sky. 
Most astronomers would agree that at present the sun should have 
the highest priority for investigation from satellites. The sun is 
such an intense source of radiation that instrumental problems are 
minimized. Further, the influence of the sun upon the earth makes 
its investigation of very great interest to geophysicists and meteor- 
ologists as well as to astronomers. Finally, the sun has been so 
thoroughly observed from the ground for several centuries that the 
goals of satellite research are already very clearly defined. 
Radiation from the sun takes the form of both photons and parti- 
cles. From the standpoint of photon radiation, the most important 
beginning project to be undertaken is the exploration of the complete 
X-ray and ultraviolet solar spectrum. The spectrum has been photo- 
eraphed from a rocket by Rense to an ultraviolet limit of about 80 A., 
from an altitude of over 200 kilometers. 'The spectrum down to 300 
A. also has been recorded by photoelectric scanning by J. Hintereg- 
ger of the Air Force Cambridge Research Center. An exceptionally 
beautiful spectrogram, obtained by the NRL on March 13, 1959, and 
covering the region from 500 to 1,800 A., is shown in plate 2. It 
can be seen that the continuous spectrum crossed by dark lines, 
which is characteristic of the solar radiation at longer wavelengths, 
terminates at about 1,600 A., and that thereafter the spectrum consists 
entirely of bright emission lines. By far the brightest line in this 
region is Lyman-a of neutral hydrogen at 1,216 A., but other lines 
arising from neutral and ionized atoms of carbon, nitrogen, oxygen, 
helium, iron, and silicon are also present. Especially noteworthy 
are the bright lines of neutral helium at 584 A., and of nine-times 
