the earth's magnetosphere. The next Explorer, RAE-B, will be launched later this year into an orbit about the moon (figure 233). In this location, RAE-B will not only be farther from the earth's radio noise, but can also use the moon as a shield from both the earth and the sun. This should make it possible to REVISED HEAO CONFIGURATION FIGURE 232 NASA SG73-3132 (2) 2-21-73 detect the low-frequency component of Jupiter's radio bursts. Further, by using the moon as an occulting screen, RAE-B may be able to identify discrete sources of low-frequency radiation if they exist. The sky looks quite different in infrared than in visible light. Infrared radiation is absorbed less than visible light by interstellar dust and gas. Thus, it was possible to find the previously discussed X-ray star Cygnus X-3 in the infrared but not in visible light. Infrared is radiated by "cool" objects and in 1972 observations were made of a cold galaxy (figure 234) and of a star that has the low temperature of 350 degrees Kelvin (170 degrees Farenheit), not even hot enough to boil water. Yet it is so large that its total energy output is 30,000 times that of the sun. The sky is uniformly aglow in the far infrared. With a balloon-borne telescope we have measured the brightness distribution over an extended range of wave number (figure 234). The result confirms a prior theoretical prediction; the spectrum corresponds to that which would be emitted by a black body at 2.7 to 3 degrees. According to the prediction, this glow is the red-shifted remnant of the light that was produced by the primordial cosmic fireball. This lends strong support for the so-called "big bang" theory of the origin of the universe. Research will continue to be conducted with balloons, a Lear jet, and on the ground through a few atmospheric windows. A major new capability will become available when the C-141 airplane with its 91-cm (36-inch) telescope becomes operational later this year. Sun/Earth Relations The sun as the life giving source of energy for earth has a special significance. In order to appreciate its role fully, we are studying processes on the sun, how their effects are transferred to earth, and the specific role they play in the power budget of earth. A variety of capabilities is needed to investigate the diverse phenomena (figure 235) that are superimposed on the steady flux of visible light from the sun. Conditions in the solar atmosphere change over a period of years following a cyclic pattern (figure 236) that is due to the evolution of the solar magnetic field. This field reverses direction about every 11 years. Large solar flares are the most spectacular phenomena observed; they tend to occur every cycle just prior to and just after the maximum number of sunspots. Most of the radiations they emit cannot be observed directly from the ground. During 1972, we observed a number of interesting events, including the most spectacular solar activity in this solar cycle. The OSO 7, Explorer 41 (IMP-G), Explorer 43 (IMP-I), and Explorer 45 (Small Scientific Satellite-I) operated during this period. On 28 July 1972, OSO 7 observed X-ray emissions from above a very active region. On the morning of 2 August a bright flare erupted, followed by another late that afternoon. Even larger flares occurred on 4 August and 7 August. The radiation hazard near earth was the greatest ever recorded, but there was no danger below our protective atmosphere. Flares occur in a hot magnetized plasma in the solar atmosphere. In a few minutes they generate more energy than man in a million years. The flare plasma is up to 1000 times as dense as its surroundings and is vastly hotter. Electrons and charged nuclei are accelerated to high energies and clouds of coronal gas are ejected. Radio noise and X-rays are emitted by electrons as they plow through the solar atmosphere. It had been speculated that the energetic nuclei, primarily protons and alpha particles, would produce nuclear reactions. During the August flares, we obtained the first direct evidence for this process by observing with OSO 7 the gamma rays resulting from such reactions. Some of the reaction products apparently can reach earth as components of solar cosmic rays. Normally less than one percent of the helium from the sun consists of the light isotope. The solar cosmic rays from two flares had as much as 20 percent of the helium in the form of He'. It is possible to follow changes in temperatures in the solar corona and in flares by using metal ions as a thermometer. As the temperature increases: more and more electrons are knocked off the atoms in the solar corona. Each charge state of an atom emits characteristic spectral lines, or "colors," which are observed and identified by OSO 7. The temperature distribution on the sun observed during the August activity will be most important for reconstructing the events (figure 237). Flares cause drastic disturbances of the interplanetary medium and the magnetosphere (figure 238). Excellent observations of these disturbances were obtained with Explorers 43 and 47 near earth (figure 239); with Pioneer 9 closer to the sun, and with Pioneer 10 at about twice the distance of earth from the sun. Most of the direct effects stop at the ionosphere, and it is generally believed that the loss of radio propagation is the main practical consequence. After the August flares, the large magnetic storms on earth also affected power transmission lines. In most cases, protective devices prevented major problems, but one power company reported an exploded transformer. Even greater effects might have been produced. On 19 December 1971, OSO 7 observed the ejection from the sun of three luminous clouds of gas with speeds of about 3,500,000 km |