A Brief History of Palomar Observatory

Credit: www.astro.caltech.edu/palomar

Since we, Ay20-ites, are going to Palomar Observatory tomorrow (Sunday 10/16), I should dig out some information before hand. Inside the big dome, the temperature is kept around 30 to 40 degree so we better bring a jacket!

The Palomar Observatory is located in north San Diego County, California around 100 miles south of Caltech. Its coordinates are 33 degree 21' 21''N and 116 degree 51' 50'' W with the altitude of 5618 feet or 1712 meter. It is a world-class instrument for astronomical research that is owned and operated by the California Institute of Technology. The observatory is consisted of five telescopes including the 200-inch telescope.

History

1908 - Mt. Wilson 60-inch telescope's construction is completed under supervision of George Ellery Hale and grants from the Carnegie Institution of Washington. At that time, it is the largest telescope sitting above the Los Angeles basin with few light pollutions. Because of its aperture, astronomers can see fainter and further away objects. Harlow Shapley, with the aid of this telescope, measured the size of our galaxy and the position of our solar system in it.

1917 - Mt. Wilson 100-inch telescope's construction is completed. Because of a large size, casting and shaping the glass mirror face technical challenges and difficulties. Moreover, it turns out to be a temperamental machine - only a small change in temperature can make the mirror change shape and out of focus. Despite these setbacks, it still provide the best of view of distant objects at that time. Edwin Hubble uses this telescope to investigate the distances and velocities of faraway galaxies which is a clue of expanding universe.

1928 - Eleven years after works at Mount Wilson are done, Hale received a grant of six million dollars from the International Education Board, a funding agency endowed by the Rockefeller Foundation for the project of another observatory. This time, the observatory is going to be operated by the newly-founded California Institute of Technology.

1930-34 - As Los Angles expands, it produces more and more light pollution which is not friendly for observing a sky at night. Hale surveys for less populated areas including sites in Arizona, Texas, Hawaii, and South America but the final result is the Palomar Mountain at an elevation of 5600 feet.

1934-36 - As mentioned before, mirror casters face technical challenges for 100-inch mirror for telescope at Mount Wilson. After spending over 600000 dollars, mirror casters are still unable to create a 200-inch mirror out of fused quartz. Hale decides to use a new glass bland called Pyrex which is less prone to temperature (much less expand or contract than ordinary glass) so it will have less problem of focus and distortion problems due to temperature which affects the 100-inch telescope. The image below shows two people standing on the unpolished mirror.

1936 - With the improvement of the road to the mountain and installation of water and electricity, the construction of 200-inch dome is completed in less than two years. "The telescope piers are anchored to the bedrock 22 feet below, while the dome supports go about 7 feet into the overlying granite."(http://www.astro.caltech.edu/palomar/history.html) Several Caltech undergraduates help pouring concrete too! The finished dome is 41 meters tall, 42 meters in diameter which is accidentally similar to the dimension of the Pantheon in Rome. 

1936 - The mirror gets transported from New York to Pasadena with a train which always traveling slower than 25 miles per hour. The telescope project gets media attention and thousands of people watch the transportation of the mirror. The trip takes 16 days in total.

1936-47 - Opticians at Caltech carefully grind and polish the mirror into a perfect paraboloid shape. The casting and annealing process causes scar tissue which occupies the top two inches of the mirror. In the end, almost 10000 pounds of glass are polished away.

1936 - The 18-inch Schmidt telescope is put into service. It is an ideal for photographing large regions of the sky scanning for interesting phenomena which are going to be carefully investigated by the bigger 200-inch telescope.

1938 - With the amazing success of the 18-inch Schmidt telescope, the construction of the 48-inch Samuel Oschin Telescope begins. It is the same design but bigger. It has a wide viewing area of 36 square degree. It is used to make detailed maps of the entire norther sky which systemically collect targets for the 200-inch telescope to study. This catalog is later used by the Hubble Space Telescope as the Guide-Star Catalog. The telescope is finished in 1948.

1941-45 - All works halt as the result of the outbreak of the World War II. The production resume on September of 1945.

1947-49 - The mirror is moved from Pasadena to the summit of Palomar on November 18-19, 1947. Since the initial images are not perfect, it takes two years to make final polishing, aligning and adjusting the mirror.

1949 - Finally, thirteen years of mirror polishing make the "Big Eye" to the desired form. It is formally named in honor of George Ellery Hale, who passed away in 1938. Edwin Hubble takes the first photographic exposure in January.

Credit: Danner/Hogg

Note: All pictures are taken from Caltech Archives, if not indicated otherwise.

I would like to end with a wonderful video containing many interesting images of the construction and importance of the Palomar Observatory.