Mount Wilson Observatory has a rich history of astronomical research and discovery spanning nearly 10 decades. As the centennial approaches, Mount Wilson Observatory continues to conduct research and develop new instruments. There are not only long-term observing projects developed during the last century in operation, but state-of-the-art telescopes and cutting-edge instrumentation operating and under development at the observatory.

From 1997 to 2000 I had the unique privilege of working at the Mount Wilson Observatory (MWO) in various capacities. I started as a volunteer telescope operator for the Telescopes in Education program (TIE), became a night assistant on 60-inch telescope, graduated to operating the natural guide star adaptive optics system on the 100-inch Hooker Telescope, then finally obtained a full-time position at the 150-foot Solar Tower, which enabled me to live on the observatory grounds.

The experiences I had during those three years could never be duplicated. Living on the mountain I was able to study first-hand the operation of many of the telescopes at the observatory. Through my participation with the Mount Wilson Observatory Association (MWOA) I became interested in the history of the observatory and went through their docent training, which further sparked my interest in the history. Working closely with Don Nicholson, President of MWOA and son of the well-known astronomer Seth Nicholson, I was privy to stories of what life was like at Mount Wilson in the early days. Those were the days when women weren’t generally allowed to use the telescopes or spend the night on the mountain in the astronomers’ quarters, a building called the Monastery, with the stock excuse that there were no bathroom facilities for women.

On every instrument that I had the honor to observe, I was reminded of the notable personalities who were there before me. When using the 24-inch TIE telescope I thought of those who designed and used it in the early 1960’s to determine the landing conditions for the Apollo moon missions. From the broken shell of the building next to the TIE dome, Edward. E. Barnard took some of the most beautiful wide-field photographic images of the northern Milky Way, unrivaled by any other in their clarity and detail at the time. When using the 100-inch Hooker Telescope I could not help but remember I was using an instrument used by Edwin E. Hubble to determine that the Milky Way is just one of many galaxies in an expanding universe. When going up the elevator of the 150-foot solar tower I would think of the 1930’s newsreel clip of Albert Einstein traveling up the tower in that same bucket (too generously referred to as an elevator), smiling and waving to the camera. Everywhere I went on Mount Wilson I was intensely aware that I was walking in the footsteps of giants.

Today many projects continue to be carried out much in the same manner as they did decades ago. The 60-foot Solar Tower uses the same white light camera developed by Ferdinand Ellerman in 1907 to photograph the Sun on every clear day. The solar observers at the 150-foot Solar Tower create sunspot drawings using the same methods as those developed in 1917. The 60-inch Telescope is once again used for public observing sessions, having such well-known visitors as author Tom Clancy and actor Jody Foster. In the 1920’s, hundreds of people would ascend upon the mountain each night to get their turn to view the heavens through the then second-largest telescope in the world. Today, the public still makes such a pilgrimage, though in smaller numbers, to spend a full night of viewing on the glorious telescope.

Which so much history surrounding the MWO staff all the time, so much of the original equipment still being utilized, so many of the original structures in existence on the grounds, it is impossible not to be reminded of the great astronomers of days gone by. To the staff who live and work at the observatory, it is fondly referred to as a ‘working museum’.

And yet, MWO does much more than continue research that was conducted in the past. It is home to a number of cutting-edge projects from optical interferometry to adaptive optics. Directly across the narrow dirt road from the large somewhat run-down building that once housed Albert A. Michelson’s 50-foot interferometer sits a small, shiny new dome housing one of the six one-meter telescopes constructed by the Center for High Angular Resolution Astronomy (CHARA) for their six-element optical interferometer. Such fascinating juxtapositions of 20^th century and 21^st century astronomy are found all over the observatory grounds. Perched on the side of the 100-inch Telescope, which was used in the 1920’s to produce some of the sharpest and most detailed views of distant galaxies, is the natural guide star adaptive optics system ADOPT developed by the Mount Wilson Institute over seven decades later, a system that gives the 100-inch even sharper vision. While adaptive optics is considered cutting-edge science, Horace Babcock first started experimenting with the concept to mechanically compensate for poor ‘seeing’, a term denoting how well or poorly the atmosphere allows an image to appear, 50 years ago on the 60-inch Telescope ⁽¹⁾.

Mount Wilson Observatory is a fascinating place. Beautiful in both its surroundings and its science, it is arguably one of a kind. There are not many places where one can so fully experience the past and future of astronomy in the same moment. My goal in writing this paper is not only to discuss the telescopes on the mountain and some of the programs in operation at the observatory, both past and present, but to describe what it was like to work there, to be a part of the Mount Wilson Observatory and its incredibly rich heritage. With this in mind, I have chosen not to deliver the information following a strict historical timeline, but rather in the order of my introduction to the different telescopes and projects on the mountain. I begin with a brief discussion of the founding of the Mount Wilson Solar Observatory, then take the reader on a journey through the past, present and future, although not necessarily in that order, of the Mount Wilson Observatory.

The founding of the Mount Wilson Solar Observatory, as it was called for the first thirteen years of it operation, is closely tied to the Carnegie Institution of Washington, which was established in 1902 to support original research in the natural sciences. During the first year of the Institute’s operation, many small grants were awarded to various scientific projects. To aid the Institution in its consideration of projects requiring major expenditures, eighteen advisory committees on different branches of science were formed.

George Ellery Hale, who was at that time the Director of the Yerkes Observatory operated by the University of Chicago, was a member of the first advisory committee on astronomy, and as such had intimate knowledge of the astronomical proposals received by the Institution. Included in this committee were other well known astronomers of the day such as Edward C. Pickering, Director of the Harvard College Observatory, and Lewis Boss, Director of the Dudley Observatory. Hale was the only member in the group who was interested in astrophysics; the other members’ research centered primarily on photometry or astrometry. In other words, they focused on measuring the luminosities or positions of the stars they observed. Only Hale was deeply interested in the physical nature of the Sun and stars. Moreover, Hale recognized the value in developing specialized instruments for the detailed study of these physical processes. At that time, most astronomers chose their research project based upon the capability of the instruments they already had, as well as the limits imposed upon their observing projects by the location of their observatories.

Hale was keenly aware that the Sun was the only star that could be studied in detail. He believed that the physical nature of the stars could be best understood through studying the Sun. Therefore, Hale desired to build a solar observatory and brought this idea to the committee. However, the original charge of the advisory committee was to recommend a number of small projects to fund, and such a large-scale project as Hale’s was beyond their scope. Moreover, it proved difficult to get the members of the advisory committee with their diverse interests to agree with the idea of a new observatory utilizing reflecting telescopes to conduct astrophysical studies of the Sun and stars.

Hale suggested that as a first step, they establish a small solar observatory on a temporary basis to determine a suitable site, then if all went well they would add the necessary instrumentation to carry out more sophisticated investigations. Included in the second phase would be the construction of a 60-inch telescope for stellar studies. Hale still had trouble gaining support for this proposal, particularly from Lewis Boss of Dudley Observatory, who was himself seeking funding for a southern observatory and support for the creation of a star position catalog. Boss’s opposition to Hale’s solar observatory was most likely due to the fact that in a real sense, Boss and Hale were competing for the same piece of the pie, and a relatively small piece at that.

In 1903 the Institution awarded a small grant to Boss, Hale, and W. Wallace Campbell, Director of Lick Observatory, to conduct site surveys for both a southern observatory and solar observatory. Among the sites chosen to investigate for Hale’s solar observatory were Mount Wilson, Palomar Mountain and Flagstaff. The results of the survey proved Mount Wilson to be not only an excellent site but the most accessible, so Hale decided to go there himself in order to prepare a more detailed report on the observing conditions, transportation issues, water and land availability, and other practical matters.

Hale first traveled to Mount Wilson in June of 1903, making the trip from the city of Pasadena in the Los Angeles basin below to the summit of the mountain on mule-back. Once there, he was willing to go to any lengths, or in this case, heights, to determine whether the observing conditions at the site were acceptable. He could often be found scrambling up tall pine trees, dragging his 3-inch telescope with him. The following is an excerpt from an entry Hale made in his diary during that expedition: "Seeing poor at tree…at 32 feet and 68 feet, seeing better…" ⁽²⁾

Hale had discovered that getting just an extra 60 feet above the ground resulted in improved seeing conditions, especially for solar observing, a discovery that he would put to use several years later when constructing the 60-foot and 150-foot solar towers. To his delight, he found the observing conditions to be excellent during the duration of his survey, with clear, calm weather and low winds, resulting in extraordinary seeing. He knew that daily observations of the Sun of the high caliber that he was seeking could be carried out at this site.

Upon his return to Yerkes, in a letter to the Executive Committee of the Carnegie Institution Hale wrote, "... the Sun’s image as observed from the summit of Mount Wilson is of remarkable sharpness. There can be no doubt... that the first images, such as we obtain here only a few times over the course of a year are often observed on Mount Wilson in the course of a single week, at least during the summer months." He continued on to say, "... it would be possible to extend indefinitely the numerous branches of solar work which require fine definition." ⁽³⁾

Equally important, Hale had confirmed that the summit was indeed relatively accessible from the well-developed city of Pasadena at the foot of the mountain, that the water supply was more than adequate, and that the Mount Wilson Toll Road Company, who held title to the land, would be willing to deed a large plot of land to the Institution on which to establish the observatory.

While impressed with Hale’s findings, the Institution was still not in the position to grant the funds that would be needed to establish an observatory of the magnitude Hale had proposed, as it had already committed substantial funds to support large projects in other scientific fields.

Hale decided to return to Mount Wilson and start building his observatory with or without the Institution’s support, even if it meant he had to fund the effort himself. He sent his family ahead to take up residence in Pasadena and arrived a few weeks later in December of 1903. At this point his salary was still being paid by the University of Chicago, as he was still the acting Director of the Yerkes Observatory, but the expenses he incurred in making the future observatory grounds habitable came out of his own pocket.

In short time Hale began his own fundraising campaign, and received a commitment from John D. Hooker, one of the founders of the California Academy of Sciences, to give money to bring Edward Emerson Barnard and his Bruce photographic telescope to Mount Wilson to continue working on his photographic atlas of the Milky Way. This was the same Hooker who would be responsible for funding the mirror in Hale’s 100-inch telescope a dozen years later, called the Hooker telescope in his honor.

Hale had plans to transport the Snow Solar Telescope which was at Yerkes, to Mount Wilson. This idea met with much opposition from Helen Snow of Chicago, the donor of the telescope, who wanted to see the instrument remain at Yerkes. Hale eventually convinced her to let him erect the Snow at first on a temporary basis, and ultimately on a permanent basis at Mount Wilson. While he was waiting for this transfer to transpire, he decided to install a smaller coelostat on the mountain known as the Wadesboro telescope, named for the town of Wadesboro in North Carolina where the telescope was used to observe the total solar eclipse of 1900. The observations he conducted with the Wadesboro further confirmed his belief that Mount Wilson was the ideal location for his solar observatory. This telescope also afforded him the opportunity to experiment with methods to improve the seeing conditions in the immediate vicinity of the telescope by shielding the horizontal tube through with the light traveled from the direct sunlight, thus decreasing the buildup of heat in the tube which was responsible for distorting the solar image. It was during this period that Hale first considered the advantages of placing a solar telescope on a tower, a design he would bring to fruition several years in the future ⁽⁴⁾.

After Miss Snow gave control over the Snow Solar Telescope to Hale, he requested a grant of $10,000 from the Institution to relocate the instrument at Mount Wilson in April 1904. Although this amount would not fully cover the costs of the construction of the rest of the observatory facilities and its operation, Hale was confident that he would be awarded this modest amount of money. In addition to granting his request for the $10,000, the Institution promised at least another $30,000 to be given to him in December of that year.

Hale was impatient and did not want to wait until December to be able to proceed with his plans. He so deeply believed in his observatory that he took it upon himself to fund the construction of a permanent building for the Snow Solar Telescope, an electrical power plant, a water system, and living quarters for the astronomers (the Monastery) on the mountain, as well as an instrument and optical shop in Pasadena. Hale knew that his act of spending the money promised to him before he received it and without approval could anger the Institution and perhaps even jeopardize his chances to receive support from them in the future, but he was willing to take that risk. If the Carnegie Institution did not fund the observatory, Hale would manage to fund and operate it himself, albeit on a smaller scale. With that in mind, on June 13, 1904, Hale signed a 99-year lease with the Mount Wilson Toll Road Company for 40 acres on the mountaintop free of rent for the term of the lease.

In the fall of 1904 Hale heard that one of the scientists who had received a $40,000 initial grant and continuing operating fees from the Institution for marine biology studies in the South Pacific decided not to proceed with his project, so the grant reverted back to the Institution. With such a large sum of money freed up, Hale had great hopes that the Institution would look more favorably upon funding his plans for a large-scale observatory that included the 60-inch reflecting telescope. He applied for a grant of $65,000 and an additional $25 – 40,000 per year for operational costs and instrument development. Hale also had to admit to spending in advance $27,000 of the $30,000 already promised to him.

Luckily for Hale, his impulsive behavior was not met unfavorably by the Institution. After reviewing his proposal, the Executive Committee recommended that Hale be awarded not $65,000 but $150,000 to be followed by the same amount the next year. This amount was far more than Hale had anticipated; if he were to be awarded the full amount he could easily establish his solar observatory with the Snow Solar Telescope and the 60-inch telescope for stellar studies. While he had support from the Board of Trustees, he was not entirely confident that he would receive such a large amount of money, as that would be the largest grant the Institution had ever made.

On December 20, 1904, exactly one year to the day after moving to Pasadena to start his venture, Hale received word of the Institution’s decision. He was on his way up the mountain when he stopped at Martins Camp, a small mountain resort about one mile below the summit, to receive a phone call over an old single-wire telephone. It must have been with much joy that Hale listened to the telephone operator read the telegram from the Carnegie Institution stating that not only had he been awarded $150,000 a year for two years, but was guaranteed the future financial support for new instruments, facilities and maintenance. Hale’s dream became a reality and the Mount Wilson Solar Observatory of the Carnegie Institution of Washington was born.

For the next forty-four years, the Mount Wilson Observatory (the word ‘Solar’ was dropped from the name when the 100-inch telescope began operating in 1917) was home to the largest solar and stellar telescopes in the world, dominating the field of astronomy and turning out an unparalleled volume of scientific research.

My first trip to Mount Wilson was with a friend of mine who worked with Telescopes in Education (TIE), an educational outreach project. I remember the trip up the winding mountain road in darkness, aware of the sheer drop of hundreds of feet off one side of the road. After a rather harrowing half-hour drive we reached the summit of Mount Wilson and entered the locked gate of the observatory. Once inside the TIE dome, I watched with interest as my friend readied the telescope for the night’s work, started the CCD camera cooling, turned on the computer and initialized the software that controlled the telescope and camera, and checked the phone line over which the students would connect via modem to assume control over the telescope and imager.

I watched as he took the telescope and imager through its paces, getting it ready for the remote observers. The first image he took to focus the CCD camera, which was the first CCD image I had ever seen taken, was amazing. In a mere three seconds there was an image of a globular cluster – a gravitationally bound collection of millions of stars – right before my eyes. Such an object is not generally visible to the naked eye, and only marginally visible with a small aperture amateur telescope such as the 8-inch reflecting telescope I owned. But with 24 inches of aperture and a couple of millimeters of silicon, an image of countless individually resolved stars appeared on the computer screen. In that moment, I knew that I was hooked on CCD imaging.

I spent the duration of the night observing my friend run the remote session. I could hear the oohs and ahs of the class-full of excited school children at the other end of the line when the image they had taken popped up on their computer screen. Something special was going on, and I wanted to be a part of it.

Telescopes in Education (TIE) is a NASA sponsored program that gives K-12 students around the world the rare opportunity to remotely control a telescope and charge-coupled device (CCD) imager. The images can be saved to a local computer where they can be processed at a later time using software developed by Software Bisque. The primary instrument is a professional-grade 24-inch reflecting telescope, which TIE has on permanent loan from Caltech, fitted with a Santa Barbara Instruments Group (SBIG) ST-6 CCD imager. This telescope, like many of the instruments on Mount Wilson, has an interesting history of research and discovery.

The telescope was designed and built by Jim Westphal (former director of Palomar Observatory), Bruce Rule, and Bruce Murray (former director of NASA's Jet Propulsion Laboratory) during the Apollo space mission era in the 1960’s. It’s purpose was to study the moon in order to determine whether the surface was covered by a thick layer of fine dust, as some scientists believed at the time. There were questions as to whether the Apollo spacecraft would be able to land on the surface without sinking into this dust. Infrared observations carried out with this telescope revealed that there was no such dust layer, and therefore landing on the moon would not prove hazardous to the Apollo astronauts.

After this distinguished duty, the telescope was put to use as a teaching tool for Caltech students where it suffered more than its share of hard knocks, then was eventually mothballed. It took the vision of Gil Clark, Robert Jastrow and Sallie Balliunas to bring the telescope out of its retirement and put it to good use once again as both a teaching tool and research instrument.

The TIE program was conceived of in the early 1990’s by Gil Clark, who was at that time an engineer at the Jet Propulsion Laboratory. While working with Boy Scouts, Clark had observed how the children came alive when looking through telescopes. His idea of developing an automated telescope that could be used remotely was to reach those students who would not generally have access to a telescope. Robert Jastrow, Director of the Mount Wilson Observatory and Sallie Balliunas, Deputy Director, heard of Clark’s idea and decided to get involved. Jastrow and Balliunas offered Clark the use of a science-grade 24-inch reflecting telescope owned by Caltech and a dome to put it on the observatory grounds. By 1993 TIE was fully operational, and since that time has served well over10,000 students from over 300 schools around the world.

While most of the students use the telescope simply to image interesting objects and take pretty pictures, some have progressed to using the system for scientific research projects. One such student was Heath Gibson, a high school student competing for the Intel scholarship. After six months of variable star observing he discovered a new variable star, determined to be an eclipsing binary ⁽⁶⁾. From such discoveries of variable stars to supplying data to help in revising the ephemeris for the planet Pluto, many TIE users have greatly contributed to the program.

From the original loan of the instrument by the Mount Wilson Institute and its reconstruction by Caltech, through its control system hardware installed by Tom Melsheimer and its control software developed by the Tom, Steve and Matt Bisque, to the numerous volunteer telescope operators that man the facility every night it operates, TIE depended upon volunteers to keep it going. I was determined to be one of those volunteers.

It was not long after that evening that I mustered up the courage to call Steve Golden, the telescope technician and program administrator, to inquire whether they were accepting any new volunteer operators. I was told that they were not, but that they would make an exception in my case. I signed up that day. After my training period of about a month, I’d be given keys not only to the 24-inch dome but to the observatory itself!

For the first time I realized the preparation involved in running an observing session. The first order of the night was to monitor and record the observing conditions – temperature, humidity, transparency, seeing, some terms I had never really been aware of. I had to think about the moon’s phase and position and the impact that would have on determining what objects could be observed and when. I had been accustomed to pointing my small telescope at any part of the sky to track down my target; this telescope had limits below which it could not be pointed and areas in the sky in which it would not track well. I became accustomed to making observing lists, carefully taking into consideration all of these concerns, as well as observing objects only near the meridian (an imaginary line that runs through the point directly overhead and due south on the horizon). I found that with adequate preparation, the actual observing a snap.

With the Windows-based control software, Software Bisque’s TheSky, I could point and click my way around the sky and the telescope would follow. Once the telescope was pointing at the desired object, I used CCDSoft to control the camera to image the object. I had to be careful to select the appropriate image exposure time, science filter, binning amount, then take darks, flats and bias exposures, all the while monitoring the camera temperature. After saving the image, I used CCDSoft to process the image into something visually appealing.

In a typical TIE session, the remote user would call on the voice line to get permission to connect to the telescope via modem. Usually the user would maintain voice contact throughout the session, often to get suggestions on what objects to image or just to chat. Once the remote user would take control of the telescope and CCD imager, all I was expected to do was rotate the dome so the shutter opening aligned with the telescope, and monitor the conditions in and around the dome. There would be one or two sessions per night lasting two or three hours apiece.

Once the remote sessions were over, the telescope was mine! I spent many hours imaging objects and processing the images to create pretty pictures. I stayed up all night on my birthday that first year, seeing how many Messier objects I could image before the Sun came up. I built a sizable image library, part of which is posted on the TIE website (http://tie.jpl.nasa.gov/tie).

 
M27, M8 and M16 BVR images taken with SBIG ST-6 on 24-inch telescope by author in 1999.

One evening while working at TIE, someone dropped by the dome and invited me to join the observing session taking place on the 60-inch. It was a night reserved for the members of the Mount Wilson Observatory Association, one of the perks of being a supporting member. I still remember walking up the metal stairway leading up to the telescope floor in the large dome eerily illuminated by dim red lights. As my eyes adjusted to the low light, I could see people standing in line at the telescope. Others were sitting in lawn chairs sipping coffee, some were snuggled in sleeping bags. I anxiously took my place in line to view Jupiter. I climbed six feet up a ladder to look through the eyepiece, which at 4-inches had a larger aperture than many amateur refracting telescopes. The view took my breath away. The image was bright, stable and crystal clear, with the colorful cloud bands clearly visible. I had never looked through a 60-inch telescope before (not many folks have), and was impressed beyond words.

Jupiter taken with digital camera through the
eyepiece of the 60-inch telescope by author in1999.

Little did I know at the time that just a few months later I would have the opportunity to operate the telescope on a part-time basis. I will never forget those moonless summer nights of operating the 60-inch, warm nights with extremely stable atmospheric conditions and sub-arcsecond seeing. Sometimes the Los Angeles basin would be covered by a layer of clouds lying a few hundred feet below the summit of the 5700-foot mountain, completely blocking the bright glow of the city lights, resulting in a sky so dark that one could clearly see the Milky Way. I wondered what it must have been like to observe on the 60-inch decades ago, before the basin below became so overpopulated, and dark skies weren’t such a rarity on Mount Wilson.

Hale had the 60-inch mirror blank for twenty years before he was able to turn it into the largest telescope in the world. He began planning for the 60-inch telescope construction in 1905, less than a year after the observatory was founded. The telescope structure and support structure was massive, and consisted of many large parts. Hale knew that it would be difficult to transport the structural pieces up the mountain on the narrow 9½ mile path up the mountain, so he decided to widen the road. He also had a special transport car designed with electric motors on each wheel, wheels that could be steered independently. The car was not adequate to carry the heavy loads, and needed to be helped along by several mules. Hale finally concluded that the job could be best accomplished by the mules alone. All 150 tons of material used in the telescope and dome were carried up the mountain by mules.

Meanwhile, George Ritchey, who had designed the telescope, was working in the optical lab in Pasadena grinding and figuring the mirror blank. This job took one and one half years to complete. In a disastrous final polishing, the perfectly-figured surface was deeply scratched rendering it unusable. The glass disk had to be reground to a sphere then refigured to a parabola, taking another four months. The telescope was completed in 1908.

One of the great advantages of a reflecting telescope over a refracting telescope is the smaller focal length. The 60-inch telescope tube is only 15 feet long, compared with the 60-foot length of the 40-inch refractor at Yerkes. This allowed the dome for the 60-inch to be much smaller as well; at a diameter of 58 feet, it is approximately two-thirds the size of the dome for the 40-inch. The telescope tube assembly, which supports the mirror with a system of levers housed at the bottom of the tube, is fork-mounted on the polar axis. The telescope is supported by a mercury flotation device beneath the fork mount in the floor below. The dome is a double-walled steel structure on a concrete foundation. The optical system was designed to be used in many different configurations for a variety of studies, from photography to spectroscopy.

In 1914, Harlow Shapley began a survey of globular clusters using the 60-inch Telescope, and by mapping out the three dimensional distribution of the clusters determined that the center of the Milky Way Galaxy was located in the constellation of Sagittarius ⁽⁷⁾. Later, the 60-inch was used to study the spiral nebulae, whose physical nature was not fully understood. The Andromeda nebula was found to have a spectrum similar to that of the Sun, leading astronomers to speculate that it was composed of stars. Then in 1919, George Ritchey used the telescope to discover novae in spiral nebulae. Photographs showed star-like condensations in some spiral nebulae, further evidence to support the theory that they were composed of stars. The final confirmation of this fact was to come some years later from Edwin Hubble using the 100-inch Hooker Telescope, and instrument that was able to resolve individual stars in galaxies outside of our own.

60-inch Telescope, taken by the author.

I was on the mountain at least one or two days every week between working at the 24-inch and the 60-inch telescopes. I decided it would be best to start spending the night on the mountain rather than make 45 minute drive home in the middle of the night or first thing in the morning after being up all night, so I was assigned a room in the Monastery. The accommodations were Spartan; the room was just large enough to fit a single bed, small desk and chair, and a small chest of drawers. The room did not have a private bathroom, but it did have a sink. The bathroom was about 50 feet down the hall – the long trek down the windowed corridor walking barefoot on the icy linoleum floor was not the most pleasant experience in the dead of night. Sometimes I would run into other residents; there was usually another couple of folks staying in the Monastery as well. Sometimes the other residents were not so friendly – the scorpions, potato bugs, and black widows that also called the Monastery their home.

The kitchen facilities for the observatory were in a building near the 100-inch called the Galley. It was not exactly a kitchen designed for a chef, but adequate to cook a decent meal for oneself. Unlike many other professional observatories, Mount Wilson does not have a large dining facility and staff to cook and clean for the visitors. If you want food, you make it yourself. But the Galley was a gathering place for the Monastery residents and visiting astronomers at mealtimes, and as such was a good place to get to meet the people on the mountain.

At one such mealtime, I met two people who were working on the 100-inch. The primary designer of the adaptive optics system, Chris Shelton, was there to perform general maintenance and tuning of the system, with the help of the adaptive optics operator Morning Roberts. They described their work and it sounded very interesting. They invited me to observe a session, and I happily accepted. I ran into Chris and Morning several times during their stay on the mountain. Near the end of that time, I was approached by Morning who asked if I would be interested in learning to operate the AO system and science camera in order to conduct queue observing for the current program. She had decided to resign from her part-time post to return to graduate school, and was looking for someone to replace her. Since I seemed to be collecting jobs at the observatory, I jumped at the chance to have one more (and to have one more set of keys!).

I had visited the 100-inch Hooker telescope before, even looked through it once on some special event night (the view was less than stunning, as I remember). I had been given the Hooker tour, been shown the cage used by Hubble for glass plate photography, walked on the catwalk encircling the outside of the dome high above the ground. I was shown the old direct current electrical panels for controlling the telescope and dome power, the original operating console and clock, and even the chair that Hubble supposedly had sat in while conducting his observations. New technology or no, being in the 100-inch dome was like taking a trip back in time.

Hale began to make plans for the 100-inch telescope even before the 60-inch was completed in 1908. In 1906 Hale placed an order for the glass disk to be used for the mirror with the Plate Glass Company of Saint Gobain in France, thanks to the generous donation of $45,000 from John D. Hooker. After many failed attempts at casting a glass disk of that size, the company was successful and the mirror blank was delivered to Hale’s optical laboratory in Pasadena in 1908. Between 1910 and 1917 the construction of the telescope and dome structure as well as the figuring of the mirror was carried out. The major challenges that were faced, such as designing a telescope tube assembly strong enough to accommodate a 4½ ton mirror, and developing a mount that would be sturdy enough to handle the telescope tube assembly were solved by Francis Pease, while Ritchey successfully ground and precisely figured the mirror blank.

Astronomer Scott Teare prepares 100-inch mirror for aluminizing.
Lighter colored swirls are bubbles in the green champagne glass. Image courtesy Gale Gant.

Following Hale’s belief of fitting the instrument to the observing project, the Hooker was designed to be used in four different optical configurations: prime focus, Newtonian, bent-Cassegrain and coudé. This change in configurations is accomplished by changing the end-piece of the telescope tube, called the cage.

Like the 60-inch, the 100-inch employs a mercury flotation device for the smooth rotation of the 87-ton telescope as it tracks objects across the sky. The rotating dome, weighing 500 tons, is supported by railroad trucks which travel on a double railroad track around the perimeter of the dome structure. For smooth operation, the railroad track is ground level to a high degree of precision.

Thanks to the 100-inch Hooker Telescope, Mount Wilson Observatory once again dominated the field of astronomy with its many discoveries. The Hooker was used to discover that the intrinsic luminosities of stars (the total output of energy per square meter of a star’s surface per second) could be determined spectroscopically. This information was used to study stellar evolution and eventually to determine the relative ages of the stars ⁽⁸⁾.

Arguably the most important and well-known astronomical discovery carried out on the 100-inch by Edwin Hubble in 1929 was that our universe is expanding. First, Hubble was able to prove that the so-called spiral nebulae, commonly believed to be located in our own Milky Way Galaxy, were actually individual associations of stars like our own galaxy. He accomplished this by discovering Cepheid variable stars in some of the spiral nebulae that he observered, to which accurate distances could be determined by the relationship between their period of variability and luminosity.

Hubble then went on to measure the recessional velocities of galaxies by means of their spectroscopic redshift, and found that the further away a galaxy was from us the faster it was moving away from us. This distance/speed relationship, known as the Hubble Constant, led him to deduce that the universe is expanding. Astronomers now believe that the universe began this expansion somewhere between 12 and 15 billion yeas ago in a cataclysmic event referred to as the Big Bang.

One of my favorite stories of what it was like to observe at the prime focus of the 100-inch was told to me by Don Nicholson, son of astronomer Seth Nicholson. When Don was a teenager in the 1930’s, his father had reserved the 100-inch for a photographic session to image Jupiter’s ninth satellite, one he had discovered years earlier while a student at UCLA, and hopefully to detect another satellite. Don was told by his father that obtaining a clear photographic image was impossible due to the telescope’s tracking errors, unless the telescope was manually guided throughout the two to three hour photographic exposure. The job of guiding the telescope had to be carried out by a very experienced observer, according to the senior Nicholson. Don was convinced that he was up to the task and begged his father to allow him to take the exposure. Nicholson eventually acquiesced. On the day of the observing session they had a practice run during the afternoon. All went well and both Don and his father were confident in his ability.

That night, they pointed the telescope toward Jupiter, and Don took his position on the observing platform. The exposure was begun, and Nicholson bade his son goodnight as he went off to get some sleep. In short time Don realized the catch in the whole procedure – it was absolutely freezing sitting on the platform in the open dome in the dead of winter! Don withstood the cold despite his lack of adequate warm clothing, and carefully guided the telescope for the next couple of hours.

Right around the time that the exposure was finished, Nicholson magically appeared, warm and well-rested, to aid in the development of the glass plate. The resulting exposure was perfect; the ninth satellite was well resolved, although unfortunately no new satellite was discovered at that time. To this day, Don muses that he thinks his father had set him up – Nicholson knew how cold it would be on that observing platform and didn’t relish the idea of carrying out the task himself! Don says that he has his father to thank for giving him the coldest experience he ever had ⁽⁹⁾.

After the 200-inch Hale Telescope at Palomar Observatory went into operation in 1948, the 100-inch was not utilized for scientific studies to the same degree it had been before. Within a few years, the Carnegie Institution and Palomar Observatory, owned by Caltech, formed a partnership and became the Mount Wilson and Palomar Observatories, a partnership that lasted until 1980. In 1969, the Carnegie Institution diverted most of its astronomy funds toward building the Las Campanas Observatory in Chile, resulting in less support for MWO. Over the years, more and more of their research was carried out at their southern observatory. Finally in 1984 the Institution removed its support from MWO completely, claming that the increasing light pollution created by Los Angeles rendered the site unsuitable for scientific studies. Luckily, not everyone agreed with this judgement. In 1986 the Mount Wilson Institute (MWI) was formed, and the Carnegie Institution handed over the management of Mount Wilson Observatory to MWI. Unfortunately, MWI was not able to support the operation of the Hooker telescope and it was closed down in 1986, and all further studies were conducted at the 60-inch Telescope. After nearly a decade a new source of funding was obtained and the 100-inch was put into service once again after receiving a major upgrade to its control system in 1994. At this time, a natural guide star adaptive optics system, ADOPT, was developed by Chris Shelton, Sallie Balliunas and Tom Schneider. It is this adaptive optics system that I was trained to operate.

Small image at left is the view looking up the tube of the 100-inch standing on the mirror (when covered).
Image at right is close-up view of secondary mirror, where the author can be seen taking the image.

CHARA’s primary scientific goal is to measure the diameter, distance, mass and luminosity of stars to a higher degree of accuracy than any other ground-based instrument. They are currently in the process of measuring stars whose diameters are accurately known, in order to calibrate the instrument. Once the array is operating at its best, the astronomers working on the project will be able to measure hundreds of stars per night ⁽¹⁴⁾.

The Snow Solar Telescope, the first permanent telescope installed at the Mount Wilson Solar Observatory, did not perform as well as Hale had expected. While he used the telescope to discover the differential rotation of the Sun, and even measure the surface temperature of some red giant stars showing that they were relatively cool, in general the images produced were distorted due to turbulence caused by heat radiating from the ground. This image distortion increased throughout the day as the ground became more and more heated by the increasingly direct sunlight.

To Hale the solution was obvious: he would build his next telescope vertically, on a tower. He calculated that by being 60-feet above the ground the image would not be affected by the rising currents of hot air. In 1907 the 60-foot Solar tower was completed enough to be put into operation. While taking Hydrogen-alpha spectroheliograms using a technique that he had developed when he was a student, Hale observed swirling patterns surrounding sunspot groups, leading him to deduce that there was a magnetic field associated with sunspots. He then used the tower’s 9-meter spectrograph to study sunspot spectra. In 1908 he photographed such a spectrum that clearly showed the spectral line being split in two due to an associated magnetic field. This was not only the first instance of Zeeman line splitting observed on the Sun giving direct evidence of a magnetic field on the Sun, but the first observation of a magnetic field being associated with any object beyond the Earth ⁽¹⁵⁾.

White light photographs of the Sun using a simple camera placed in the focal plane of the telescope developed by Ferdinand Ellerman were begun in 1907. The camera, which was built in 1905 for use on the Snow Solar Telescope, was never meant to be a permanent part of the 60-foot’s instrumentation. Although a different camera was specifically designed for use at the 60-foot tower, Ellerman’s original camera outperformed the newer rotating camera, so the focal-plane camera was reinstalled and the programs of taking white light photographs continued.

In yet another example of early observational programs employing original instrumentation still continuing today, Ellerman’s camera is used to take direct photographs of the Sun daily, resulting in the largest collection of white light solar photographs in existence. Through these photographs, the size, number and motion of sunspots continue to be monitored.

More recent discoveries include Robert Leighton’s discovery in the early 1960’s that the surface of the Sun oscillates over a 5-minute period. The method used by Leighton to detect this motion was suggested by Hale decades earlier. By taking spectroheliograms in Zeeman split blue and red shifted spectral lines (indicating motion toward and away from the observer) then combining the two images to forma ‘difference’ photograph, direction and velocity could be measured. The resulting velocity maps show the up and down motion of the solar surface (Doppler shift). Thus began the field of helioseismology.

Helioseismological studies continue at the 60-foot solar tower under the direction of Edward Rhodes from the University of Southern California. The 60-foot is part of the High Degree Helioseismology Network (HiDHN) along with the Crimean Astrophysical Observatory in the Ukraine, other groups such as the Global Oscillation Network Group (GONG) and the Birmingham Solar Oscillations Network (BiSON). The studies by these groups have revealed that the solar oscillations are manifestations of standing waves trapped within the solar interior. The five-minute period discovered by Leighton is the strongest resonant mode of oscillation, while a multitude of more discreet modes have been discovered as well, and are being used to study the internal structure and dynamics of the Sun.

The mountain is a close-knit community. There are about 15 full-time residents, a couple of part-time workers and occasional visiting observers. As with any small community, news travels fast. If one didn’t run into folks at the galley, all one need do is to make a visit to the Post Office, about 300 yards outside the observatory grounds, to catch up on the news. I heard through the grapevine that there was a full-time position opening at the 150-foot Solar Tower. At first I was not particularly interested. Astronomy in the daytime? Who needs it! Get up early in the morning just to look at the sun day after day? Boring! Not a job for a night owl like me, I said. Then I heard the magic phrase – "you would get to live in a house on the observatory grounds". Live on the mountain? In a house with a huge fireplace, not in a cold little Monastery room? I’d have a private bathroom that I could keep heated for those middle of the night visits during the dead of winter? Where do I sign up!

Within a few days I applied for the position, and received a favorable response. I was first approved by the senior solar observer, Larry Webster. That was not surprising, as we were already somewhat acquainted and he knew of my dedication to the observatory. Then I successfully interviewed with UCLA astronomer Roger Ulrich, the head of the 150-foot program. The final test was a trip up the tower in the elevator.

The elevator is no more than a large rectangular metal bucket, suspended from the top of the tower, that operates like a dumb-waiter – tug down on the cable, the bucket goes up; tug up on the cable, the bucket goes down. The job would require me to make the trip up the tower to the platform where the optics were located once or twice a day, so being comfortable with the quaint elevator and unafraid of heights was a necessity. Despite the butterflies fluttering wildly in my stomach as I looked down at the receding ground when taking my first trip up the tower, I enjoyed it. I was not about to let some primal fear of heights get in the way of a job opportunity. Once I got onto the telescope platform, I quickly forgot my fear. I was in a tower rising 150-feet above the observatory grounds, and the view of the surrounding mountains and the city below was enough to take my breath away. I had passed the elevator test; the job was mine if I wanted it.