Eclipses Of The Sun And Moon (1965)

Early in the morning, a powerful jet prepares for takeoff from Edmonton, Canada. Inside, special equipment for a mission that would take its crew of astronauts, physicists, and astronomers on a race with the shadow of the moon. Okay. From the air, the scientists in this flying laboratory would observe and record one of nature's most spectacular displays, a total eclipse of the [Music] sun. For most men, a total eclipse is a sight of awesome beauty. But to scientists, it is a unique opportunity to investigate features of the sun that are normally blatted out by its blinding light. Why do eclipses occur? And what can scientists learn from them? [Music] The sun, the source of all man's energy. Around it, the Earth moves in perpetual orbit. And around the Earth, its smaller satellite, the Moon, also journeys in orbit. Both are illuminated by the sun. Occasionally, the shadow of one body falls on the other. We call this an eclipse. These are actual telescopic pictures of one kind of solar eclipse. There are in fact several kinds. To understand them, we must know something about the shadows cast by the Earth and Moon. These consist of two distinct regions. an inner cone of dense shadow called the umbra and a surrounding region of partial shadow called the penumbra. When a solar eclipse is seen from the region of the earth covered by the penumbra, only a part of the sun's surface is hidden by the moon. This is a partial eclipse of the sun. But when seen from the area covered by the dense shadow of the umbra, the sun is completely blocked out by the moon. This is a total eclipse of the sun. The sun is actually 400 times larger than the moon. Yet during an eclipse, they seem almost the same size. What accounts for this? Another kind of eclipse occurs when the moon as it moves around the earth falls into the earth's shadow. This is a lunar eclipse. Let's watch an actual eclipse of the moon. This film taken through an observatory telescope shows the moon, many times enlarged, entering the Earth's umbra. It will take the moon approximately 2 hours to pass through the shadow area. In that time, it will have traveled some 5,000 [Music] mi. Now, as the lunar eclipse ends, the moon emerges from the Earth's shadow. Notice the shape of the Earth's shadow on the moon. What did this suggest to early astronomers about the shape of the [Music] earth? The moon orbits the earth approximately once every month. Yet, eclipses of the sun and moon do not occur monthly. Why is this so? Imagine a straight line extending through the sun and the earth and beyond the earth on the other side. If the moon passed directly through this line in its journey around the earth, we would see monthly eclipses of both the sun and the moon. But the moon does not travel this way. Instead, the moon's orbit places it either above or below the line on most of its revolutions. Unless the three bodies are in position on the line, the shadows of both Earth and Moon fall off into space and no eclipses occur. Even when the moon's umbra reaches the Earth, it usually covers an area no more than 60 m wide. It sweeps across the planet at more than500 m an hour, passing ground observers in less than 7 minutes. A plane flying with the eclipse shadow can extend observations for a few minutes longer. But on the ground, only those people in the narrow path of the moving shadow can observe and record a total eclipse of the sun. Consequently, scientists often travel to remote regions to be in the shadow path. For the next few moments, we will join an eclipse expedition and see a total solar eclipse as a scientist does. Outside the observation compound, the clouds darken and semi twilight bathes the landscape, announcing the approach of totality. Now through the telescope, totality itself. Let's look at the eclipse again, stopping the camera at several points. Just before totality, we see only a thin crescent of the sun's chromosphere, the gaseous atmosphere that envelops the sun. The spots at the sun's opposite edge are called prominences. A special lens shows these prominences in detail. They are actually super hot portions of the chromosphere's gas thrown out with explosive force in long flamelike tongues. The prominences travel as far as a quarter of a million miles outward from the sun at speeds as fast as 250 m an hour. The eclipse proceeds to totality. Now the sun is completely covered by the moon, allowing us to see the faint pearly glow of another gaseous layer surrounding the sun and its chromosphere. This outer layer is called the corona. The gases of the corona are thin and they reflect and scatter light to produce the halo effect. In this view, clouds in the Earth's atmosphere obscure the full extent of the corona. But as the clouds pass, the full corona appears, extending more than half a million miles outward from the sun. This is the prime target of most eclipse expeditions. Its temperature is almost a million degrees, and data recorded from it give scientists a unique opportunity to study characteristics of high temperature gas. Occasionally, the outermost rays of the corona reach as far as the Earth, where they heat our upper atmosphere, influence our magnetic field, and probably our surface weather. The shimmering aurora or northern lights is caused by radiation from the corona. All photographs and observations of the corona must be quick and precise. For in less than 2 minutes, the moon passes on and the full light of the sun returns as quickly as it vanished. And so from the brief passage of a shadow across the Earth, scientists gain new knowledge of the sun, new data and measurements that only an eclipse will yield. But in spite of modern technology, eclipse information must be built up slowly, for all total eclipses occurring in one lifetime add up to less than 2 hours in time. Because the sun's heat, light, and gas intimately affect all life on Earth, eclipse studies are extremely important to us. But our sun is only one single star among millions in a firmament whose size defeats imagination. Recently, we have been able to cross the threshold of space. But how far into its vast reaches can we travel? How much can we discover of the universe in which our earth is only an infinite decimal speck? [Music] [Applause]