Category: Technology

These views within the McMath–Pierce solar telescope enclosure were captured during a guided tour of the instrument, April 20, 2005. By way of orientation, the observation room we visited is near the location labeled “4” on the model of the following photograph or the “Observation Room” of the drawing.

We learned each of the sets of mirrors is considered a separate telescope. The first step in designing the new solar telescope was to determine the optimal image scale. Working on the spectra of the solar granules, on the physical structure of the sunspots and their associated magnetic fields, requires a considerable image size. Past experience has shown that the optimal image of the sun should be approximately 0.91 meters. The highlight of our visit to the Main Observation room was meeting with the technician operating the recently developed low-cost adaptive optics system.

Tip-tilt correction and low order wavefront correction is available with a number of portable optical benches.  These are primarily used with the Main spectrograph and the Solar Stellar spectrograph on the Main telescope, but due to their compact mounting they could be used with other telescopes and instruments in the facility.

This configuration uses a rapidly deformable mirror to correct distortions introduced by the turbulent atmosphere. Using sensors to measure the degree of image distortion, the adaptive optics system adjusts the shape of the mirror accordingly and converts a blurred image into a clear one. The following image demonstrates the correction. “Low-cost” = $25,000 in 2003 US dollars. Under references is a link to a full description of the device by the creator.

A main area of ​​study in the observatory is the structure of sunspots, which are relatively cold, dark spots on the surface of the Sun created by intense magnetic activity.

Some of the most important discoveries made at McMath-Pierce include the detection of water vapor in the Sun, the measurement of kilogauss magnetic fields (thousands of times stronger than those on Earth) outside sunspots and the detection of a natural maser (like a laser, but with a microwave instead of visible light) in the Martian atmosphere.

Over the years and technological advances, the National Solar Observatory has moved its headquarters from Tucson to Boulder, Colorado. The organization abandoned its solar telescopes at Kitt Peak and in New Mexico for a larger instrument in Hawaii, the Daniel K. Inouye Solar Telescope on the island of Maui, which began operating in 1919.

References:

Wikipedia “McMath–Pierce solar telescope”

“Low Cost Adaptive Solar Optics” by Christopoher Kellar

Insights into the architectural design.

National Solar Observatory website..

Copyright 2022 Michael Stephen Wills All Rights Reserved

These views within the McMath–Pierce solar telescope enclosure were captured during a guided tour of the instrument, April 20, 2005. By way of orientation, think of yourself at the location labeled “4” on this model. This is the only large telescope where humans can view the interior and visually experience the light paths “bouncing” between the mirrors.

McMath–Pierce solar telescope has three heliostats mounted on a 110-foot tower adjacent to a slanted enclosure. The 2.03-meter heliostat feeds a 1.61-meter primary mirror, there are 1.07-meter and 0.91-meter primary mirrors fed by a pair of 0.81-meter heliostats. Here we are inside the slanted enclosure, looking up the shaft to the tower mounted heliostats, readily identified as the three circles, the largest at center (3.51 feet in diameter). The smaller (2.66 feet) heliostats named “East” (on left) and “West.”

Built in 1962, the building was designed by American architect Myron Goldsmith and Bangladeshi-American structural engineer Fazlur Rahman Khan. It was the largest solar telescope and the largest unobstructed aperture telescope in the world. It is named after the astronomers Robert Raynolds McMath and Keith Pierce. Painted white to reflect sunlight to reduce heat accumulation, the enclosure is water cooled to prevent convection currents through the column of air within the slanted enclosure, keeping the air as still as possible along the light path between the mirrors.

In the three photographs following, we face the underground portion of the slanted shaft and (what looks to be) the 0.91 meter (2.99 feet) primary concave mirror. I say that because in some of the photographs a beam of light, to the left of the mirror, can be seen travelling further underground, presumably to the largest primary mirror. As there is only one such light beam, I conclude the west heliostat is inactive.

Here we looking up the slanted enclosure. Look carefully at the first photograph, below, to see reflections on the glass partition. The observation platform was separated from the light paths to maintain the stillness of the air column. The two mirrors of the first photograph are the third mirror, reflecting concentrated sunlight from the 0.91 and 1.61-meter primary mirrors into the observatory rooms. The mirror for the 1.07-meter primary is out of sight in foreground, I believe this set of three mirrors (West heliostats, primary and third) was out of service.

The second photograph, on right, is a close up of the third mirror for the largest primary. A foreshortened, perfectly round light disk is clearly visible.

Here we are inside the slanted enclosure, facing the underground portion of the slanted shaft and (what looks to be) the 0.91-meter primary concave mirror. In the lower right corner is the reverse side of the third mirror for the largest primary mirror, the 1.61-meter.

Reference: Wikipedia “McMath–Pierce solar telescope”

Copyright 2022 Michael Stephen Wills All Rights Reserved