HISTORY OF THE SOLAR OBSERVATORY
The National Solar Observatory/Sacramento Peak is located in southern New Mexico at the height of 9200 feet (2800 meters) in the Sacramento mountains. This site, chosen in 1947, overlooks White Sands Missile Range in the Tularosa Basin. The dry air of the southwest, isolation from any major source of air pollution, and plenty of sunshine make this an excellent site for observing the Sun.
The staff presently consists of research scientists, engineers, technicians, and support staff. In addition, scientists from other observatories and universities around the world come to the National Solar Observatory/Sacramento Peak to pursue research, along with many students in astronomy who work here during the summer months.
GRAIN BIN DOME
In 1950, the Grain Bin Dome was the first telescope dome built in Sunspot. The Observatory ordered the grain bin from a Sears catalog and modified it for use as a telescope dome. A 6-inch prominence telescope was mounted on a 10-foot spar inside for observing the limb (edge) of the Sun. The modifications included a slit in the roof and the ability to rotate so that the telescope could track the Sun. From March 1951 through 1963 daily flare patrol images were taken from the Grain Bin. Additional or newer telescopes were installed in 1952, 1955, and 1957. In 1963 the solar patrol duties of the Grain Bin were transferred to the then newly built Hilltop Dome.
The Grain Bin Dome seems not to have been used after 1963, until a night-time telescope was installed in 1995. Sunspot residents can now use that telescope to look at the night sky. Over the years that the Grain Bin Dome was not in use, the trees around the Dome have grown, limiting the amount of observable sky.
EVANS SOLAR FACILITY
The Evans Solar Facility is housed in the Big Dome, which was completed in 1952. There are two main telescopes in this facility: a 16" coronagraph and a 12" coelostat. Each of these telescopes can be used to feed one of several instruments. This means that two observing programs can be run simultaneously.
The Evans Solar Facility is used most often to look at the corona: the faint outermost layer of the Sun. Because the visible disk of the Sun is so bright, one cannot usually see the corona. The main telescope in the Big Dome is a coronagraph. It has a disk inside that blocks off the bright disk of the Sun simulating an eclipse, so the scientists can study the faint corona.
Most of the time, the scientists that use this facility investigate solar flares, a magnetic field high above the visible surface of the Sun, and filaments (which are called prominences when they are seen sticking beyond the bright disk of the Sun).
The Evans Solar Facility has no fixed observing program. Scientists are able to point the telescopes wherever they want on the Sun and to use whatever filters or other special equipment they need to complete their research.
The Hilltop Dome was completed in 1963. As with the Evans Solar Facility, the roof of the building (with the doors in it) can rotate around to allow the telescope to see the Sun anywhere in the sky. This telescope is used for taking patrol images of the whole Sun. These images are used to discover when something interesting is happening on the Sun, such as a solar flare, and to have a record of what the Sun looks like every day.
The Hilltop Dome contains several telescopes that have one task only: to look at the whole Sun all the time that the Sun is visible. Pictures are regularly taken through these telescopes; most of the time at the rate of one picture per minute, but more if it is likely that something interesting will happen. The Hilltop Dome telescope takes two kinds of pictures: ones that show what the Sun looks like to the human eye, and others at a particular color (with a wavelength of 6563 Angstroms) that is affected by hydrogen atoms in the Sun. In such pictures, faculae, filaments, and solar flares stand out much better than in ordinary pictures.
The Hilltop Dome pictures form an archive of observations of the Sun. It allows scientists to see the largest possible number of interesting things on the Sun (such as solar flares), even if the other telescopes at the observatory are looking at other parts of the Sun. If a solar flare is seen, then we can go back to the archive and check if something happened earlier that can help us predict when the next one will come.
This structure contains an entrance window and two mirrors that guide the light of the Sun down the tower in an evacuated tube from which the air has been removed. The tower is an impressive 136 feet (41m) tall, but the building has 228 more feet (72 m) below ground, so most of the building is in fact not visible. After the light has hit the two mirrors at the top, it goes straight down the tube at the center of the tower until it hits the primary mirror, 188 ft (57 m) below the ground. The primary mirror is 64 inches (163 cm) in diameter. It focuses the light and sends it back up to ground level, where it exits the vacuum tube and can be guided into the scientists' experiments on the optical benches.
The rotating part of the telescope weighs more than 200 tons. It is suspended at the top from a ring- shaped container holding 10 tons of mercury. The central tube is hanging: it does not sit on anything. Because mercury has very low friction, it is fairly easy to rotate the 200 tons of tube and instruments.
The kinds of things on the Sun that scientists investigate using this telescope include granulation, sunspots, faculae, weak magnetic field, filaments, and solar flares.
Sunspots are associated with strong magnetic field on the Sun. As the magnetic field twists and turns, it builds up a tremendous amount of energy. This energy can be released explosively in what is called a flare. Eruptive phenomena such as flares can eject particles which can reach the Earth. This can result in the Aurora Borealis, or Northern Lights, seen frequently at higher latitudes and it can also lead to the disruption of some radio communications.
Understanding of the Sun can also be gained by looking at the area where there are no sunspots. This spot-free area is known as the "quiet" sun. The fine, mottled background of the quiet sun is called granulation. Each bright granule represents hot gas rising from below. As the gas cools and falls, it becomes darker; creating the dark lanes between the brighter cells of rising gas. The rising, spreading motion of hot gas causes the magnetic field to collect in the dark lanes.
A wealth of information is obtained by spectral analysis, and much of the work done at National Solar Observatory/Sacramento Peak is based on spectroscopy. By examining the solar spectrum, it is possible to determine the sun's chemical composition, its temperature, the motions of its surface gases, and the strength of the magnetic field.