Unusual Telescope Reveals Sun’s Mysteries

WE HAD taken a day off to picnic in the cool Lincoln National Forest in southern New Mexico, trying to escape the desert’s heat for a while, when we saw a sign that directed us to the Sacramento Peak Observatory at Sunspot, near Cloudcroft, New Mexico. Our curiosity now aroused, we drove to Sunspot.

No one in our small group was used to the high altitude of 9,200 feet [2,800 m], and all of us were out of breath as we walked up the path to visit the telescopes housed on the peak in odd-​shaped buildings. We expected a domed building, so we were not disappointed when we saw the Hilltop Dome, but we found that visitors were not allowed to enter. Then we saw a strange-​looking building.

It was a tall, narrow-​base, triangular building rising out of the ground, and it was open to visitors. (See photo, next page.) We soon found ourselves in a laboratory housing a long telescope suspended from a bearing in the top of the tower high above us. Signs warned us not to step on the platform and disturb the balance of the instrument.

Making the Sun “Stand Still”

In a small reception room, colored diagrams explained what was being studied, and it was interesting to see that this complex of buildings is devoted to the study of the sun. We asked one of the scientists working there if this was a project to learn how to get energy from the sun. He explained that it was not that type of study but that it was a basic research project to gather information about the sun and its effect on the earth’s atmosphere and upon space in the solar system. Also, scientists are studying the interior of the sun by constantly observing its surface.

Our guide explained that the observatory was located there because the dry mountain air and lack of pollution make it a good site. Established in 1951, it was one of the first of its kind built in the United States to be devoted to the study of the sun. A diagram nearby showed us that this large tower projects 136 feet [41 m] above ground but that another 193 feet [59 m] of the telescope lie buried below ground. Thus, the telescope has a total length of 329 feet [100 m], the length of a football field! There is an almost total vacuum inside the telescope tube so that when sunlight enters, it is not distorted by heated air. This allows for reflected images of unusual clarity, providing researchers outstanding views of the sun’s surface.

The whole telescope (weighing over 250 tons) hangs from a mercury-float bearing, allowing the telescope to rotate freely to compensate for the earth’s rotation. Thus, the telescope can be directed at the sun for long periods, so that the sun effectively “stands still” in relation to the telescope. It is designed to observe and photograph very small features of the sun’s surface, the photosphere, and in the sun’s lower atmosphere, the chromosphere.

Grain Bin Dome

As we returned to our car, we passed an unusual building that to us looked like a round farm silo. And that was exactly what it was! It is called the Grain Bin Dome and was purchased in the early days of the observatory from Sears Roebuck and Company; it was modified to house the first telescope at Sunspot. At that time, space travel was being planned, and there was need for information about how the sun affected the atmosphere of the earth, especially in creating disturbances that might be caused by unusual sun activity.

Later, in 1957, a nonprofit organization, AURA (Association of Universities for Research in Astronomy, Inc.), was organized in connection with the Kitt Peak National Observatory in Tucson, Arizona; the Cerro Tololo Inter-​American Observatory in La Serena, Chile; and the Space Telescope Science Institute in Baltimore, Maryland. AURA felt that by sharing scientists and information, all could gain more understanding of the sun. We were beginning to see that this isolated observatory had connections in various parts of the earth.

[Diagram/​Picture on page 23]

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Mirrors (136 ft [41 m] above ground)

Ground level

Vacuum tubes rotate (250 tons)

193 ft [59 m]

221 [67 m] ft below ground

[Credit Line]

From a sketch by National Optical Astronomy Observatories