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.
The Quivering Sun
Dr. Bernard Durney, a research director, graciously offered to answer some questions about the sun. He explained that he is working in the field of solar seismology. We needed an explanation of what that meant. It seems that it was first studied there at Sacramento Peak. He explained: “The sun not only rotates on its axis but moves in many other ways that can be studied by viewing its surface constantly and seeing changes that occur. From these changes, we can formulate ideas about what may be occurring inside the sun and then plan studies to confirm or disprove our ideas.”
“About 1970,” he continued, “a quivering, or shaking, of the sun was predicted. It is much like the shaking, or vibration, that occurs when a large bell is rung. One can also think of the illustration of a pebble thrown into a pond and how it causes the entire surface of the pond to be affected as the rings of waves cross the pond from the point of impact. The difference is that the waves in the sun go throughout the sun in all directions.”
It appeared that these vibrations originated at different levels, some beneath the surface and others from deeper within the sun. Because of these studies, it is known that the sun expands slightly and then contracts again about once an hour, much as if it were breathing. An investigator first saw these movements of the sun in 1975. In 1976 Russian scientists also reported a rising and falling of the sun’s surface.* It was not until 1979-80 that this vibration was confirmed, partly at the Sacramento Peak Observatory.
“Actually,” Dr. Durney continued, “the sun has many unusual movements. Since everything on the sun is gaseous, parts of the sun’s surface can rotate faster than others. . . . By constantly viewing the sun as we do here at the Sunspot observatory, we can determine how the inside of the sun is rotating. . . . Since the sun rotates faster at its equator, much mixing occurs on the surface, and this causes many strange phenomena. This unusual movement creates magnetic fields deep inside the sun, which float to the surface. Sunspots on the sun are a manifestation of these magnetic fields.”
Observing the Sun Day and Night!
Dr. Durney explained: “We really need to observe the sun continuously so that we can see all the activity and all the changes on the sun’s surface. Since the earth rotates every day, it is not possible to do this in one place on the earth’s surface. That means that there is a need for solar observatories all around the earth.”
At present this is not possible, but Dr. Durney told us that, in 1980-81, some of the scientists from Sacramento Peak traveled to the Antarctic to view the sun during three three-month periods. The sun does not set for up to three months in the Antarctic, and therefore it can be observed continuously day and night by one telescope. It was interesting to learn that the gathering of this information involved so many places on the earth. Scientists hope some day to be able to classify all the sun’s vibrations and interpret them so as to understand what is happening inside the sun. Investigators now have prospects of forming an earth-wide network of observatories to do this.
Solar Flares and Corona
“What else is being studied here at Sacramento Peak?” was our next question to Dr. Durney. He told us of the solar flares. “These tremendous flares burst from the sun’s surface outward millions of miles into space, ejecting particles that disrupt radio communications when they arrive at the earth. There is also a continuous flow of particles out of the sun called the solar wind. This slows down the rotation of the surface of the sun, which in turn acts on the rotation deep inside the sun. The result is that as the sun ages, it rotates slower and slower. How the solar interior reacts to the braking of the surface is one of the things we study here.”
Another study being performed at the observatory involves daily taking pictures of the sun’s corona. These pictures reveal how the heat around the sun changes daily. Diagrams are prepared that show the distances that high temperatures extend from the sun. These diagrams change daily and provide useful information for space travelers.
Sun’s Vital Role
Energy from the sun is needed for life to continue on earth. It affects us, our vision, and the earth’s plants and animals. A study published in 1979 shows that there is evidence of a 22-year cycle of drought in the western United States that seems to be related in some way to the complete sunspot cycle of about 22 years. This is one reason for interest in the sun’s activity and its possible influence on the weather.
In the 1950’s the Sacramento Peak Observatory was one of the first to help determine the solar constant, which is the total units of power reaching an object in space at the distance of the earth from the sun. Possibly more important is how much the solar constant may vary.
Sunspots are one of the more interesting features of the sun and one that affects us on earth. Sunspots were first observed by Galileo. Later it was determined that a sunspot cycle lasts 11 years and that a complete sunspot cycle has two 11-year periods of sunspot activity. As Dr. Durney explained: “Sunspots are magnetic fields. They are dark because they block the motions that transport energy. Flares are thought to be caused by the annihilation of these magnetic fields on the sun’s surface, which then release enormous amounts of energy that affect us by disrupting radio waves and by electrifying parts of our atmosphere. This energy also causes what are called northern lights and southern lights, or auroras, a wonder to mankind throughout history.”
Sun studies may help to predict the geomagnetic storms that may occur in our atmosphere when there is sunspot activity. These affect world communications and thus the activities dependent on good radio communication, such as air travel. Because of the high cost of satellite transmission, most communication is still done by means of radio transmitters on the ground. The energy released by sunspots disrupts the shell of ionized particles surrounding the earth that reflects the radio waves back to earth. When the shell is ineffective, radio messages are lost.
More about sunlight needs to be known. Plants that produce our food depend on sunlight to make the sugars and other chemicals in our food. Photochemical reactions caused by sunlight allow us to take photographs both in black and white and in color. Therefore, it seems prudent to many to learn all that they can about our nearest star.
From our short visit to Sunspot and from talking to experts, we came to realize that we are quite limited in our knowledge of the sun. Most of us appreciate the sun on a cold winter day and wish it were not so hot in the summer months, and that is about all. We enjoyed our glimpse into the more technical side of the sun. All of us had to conclude that mankind is really just beginning to comprehend the wonders of our beneficent star, the sun.—Contributed.
The Soviet Union has an impressive solar research agency based in Irkutsk, Eastern Siberia. They have the world’s most powerful solar radio telescope, consisting of 256 antennae that synchronously track the sun from its rising to its setting.
[Box on page 24]
What Do Sun Temperatures Mean?
The book Life and Death of the Sun, by John Rublowsky, explains on pages 59 and 60: “We should understand something about the meanings of temperature. There are two different kinds. One is called ‘kinetic temperature’; the other, ‘radiant temperature.’ Kinetic temperature is the measure of the average molecular motion of a particle. The faster this motion is, the higher the temperature. When we speak about the temperatures of the solar atmosphere, we speak about this kinetic temperature. What we are saying, then, is that the average speeds of motion of the particles in the solar atmosphere increase as we go upward from the photosphere. Though these particles have temperatures of millions of degrees, they could not blister your skin.
“Radiant temperature, on the other hand, is a measure of the amount and quality of the radiation given off by matter. When we speak of temperatures deep inside the sun, we use the word in this sense. The temperature of a flame is also a radiant temperature.
“But we cannot use the concept of temperature in this radiant sense when we speak of the solar atmosphere. If the temperature of the corona were at a radiant temperature of 1,000,000 degrees [Celsius], the atmosphere of the sun would be so bright that we could not see the photosphere. In fact, if this were the case, the atmosphere of the sun would give off so much radiation that Pluto, the planet farthest from the sun, would be vaporized from the intense heat. It is a good thing for us that the temperature of the solar atmosphere is a kinetic temperature rather than a radiant temperature.
“This does not mean that the solar atmosphere gives off no radiation at all. Not only does it emit a great deal of radiation, but it gives off a very peculiar kind. The highest parts of the corona give off X rays as well as some visible light, and the lower parts give off ultraviolet light. This radiation is very important for the earth because it produces the different layers of the earth’s atmosphere.”
[Box/Diagram on page 25]
The Sun—Earth’s Star
The sun is a huge furnace supplying life-supporting heat and light to our earth. This vast ball of mainly hydrogen gas is so large that it could hold over a million earths! Yet, as stars go, it is not among the largest. As scientists are finding out, this energy source is full of subtleties. For example, “most of the visible light emanates from a region within the photosphere only about 100 km [60 mi] thick.” Yet, the sun’s radius is calculated to be 432,651 miles [696,265 km].—The Sun, by Iain Nicolson.
The Sun’s Design
THE CORE—The nuclear “burning” zone at the sun’s center where the highest temperatures are found.
THE RADIATIVE ZONE—Energy from the core transfers by radiation through this zone as gamma rays and X rays.
THE CONVECTIVE ZONE—A cooler region through which energy from the radiative zone travels by convection.
THE PHOTOSPHERE—Practically all the sun’s light is emitted from this apparent surface of the sun. It is to some extent transparent, and “it can be observed down to a depth of a few hundred kilometers.” (The Sun) The temperature is about 10,000 degrees Fahrenheit [6,000° C.].
THE CHROMOSPHERE—Seen only during a total eclipse of the sun. Tenuous layer of gas a few thousand miles thick but hotter than the photosphere, about 18,000 degrees Fahrenheit [10,000° C.].
THE CORONA—Visible only during a total solar eclipse, when it appears as plumes and streamers extending over great distances and having very high temperatures.
[Diagram] (For fully formatted text, see publication)
From a sketch by National Optical Astronomy Observatories
[Diagram/Picture on page 23]
(For fully formatted text, see publication)
Mirrors (136 ft [41 m] above ground)
Vacuum tubes rotate (250 tons)
193 ft [59 m]
221 [67 m] ft below ground
From a sketch by National Optical Astronomy Observatories
[Picture on page 26]
[Picture on page 26]
National Optical Astronomy Observatories