The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715-foot (1,742 m) peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observatory contains two historically important telescopes: the 60 inches (1.5 m) Hale telescope built in 1908, and the 100 inches (2.5 m) Hooker telescope, which was the largest telescope in the World from its completion in 1917 until 1948.
Due to the inversion layer that traps smog over Los Angeles, Mount Wilson has naturally steadier air than any other location in North America, making it ideal for astronomy and in particular for interferometry.The increasing light pollution due to the growth of greater Los Angeles has limited the ability of the observatory to engage in deep space astronomy, but it remains a productive center, with many new and old instruments in use for astronomical research.
The observatory was conceived and founded by George Ellery Hale, who had built the 40 inches (1.0 m) telescope at the Yerkes Observatory. The Mount Wilson Solar Observatory was first funded by the Carnegie Institution of Washington in 1904, leasing the land from the owners of the Mount Wilson Hotel in 1904. Among the conditions of the lease was that it allow public access.
60 inch (1.5 m) Telescope
George Ellery Hale received the 60 inches (1.5 m) mirror blank, cast by Saint-Gobain in France, in 1896 as a gift from his father, William Hale. It was a glass disk 71⁄2 inches (190 mm) thick and weighing 1,900 pounds (860 kg). However it was not until 1904 that Hale received funding from the Carnegie Institution to build an observatory. Grinding began in 1905 and took two years. The mounting and structure for the telescope was built in San Francisco and barely survived the 1906 earthquake. Transporting the pieces to the top of Mount Wilson was an enormous task. "First light" was December 8, 1908. It was at the time the largest operational telescope in the world.
The 60 inch reflector became one of the most productive and successful telescopes in astronomical history. Its design and light-gathering power allowed the pioneering of spectroscopic analysis, parallax measurements, nebula photography, and photometric photography. Though surpassed in size by the Hooker telescope nine years later, the Hale telescope remained one of the largest in use for decades.
In 1992, the 60 inch telescope was fitted with an early adaptive optics system, the Atmospheric Compensation Experiment (ACE). The 69-channel system improved the potential resolving power of the telescope from 0.5-1.0 arc sec to 0.07 arc sec. ACE was developed by DARPA for the Strategic Defense Initiative system, and the National Science Foundation funded the civilian conversion.Today, the 60 inch telescope is used for public outreach. Eyepieces are fitted to its focus instead of instruments. It is the largest telescope in the world devoted to the general public. As of June 2009, the cost for a half-night of observation is $900, $1700 for a full night.
100 inch (2.5 m) Hooker Telescope
Once the 60 inch telescope project was well underway, Hale immediately set about creating a larger telescope. John D. Hooker provided crucial funding for it, along with Carnegie.The Saint-Gobain factory was again chosen to cast a blank in 1906, which it completed in 1908, After considerable trouble over the blank (and potential replacements), the 100 inches (2.5 m) telescope was completed and saw "first light" on November 2, 1917. The blank started with over two tons of fused glass which was melted in a furnace into one piece. The blank once melted into one piece took over a year to cool without cracking.
Just like the 60" telescope, the mechanism incorporates a mercury float to provide smooth operation. The Hooker telescope was equipped in 1919 with a special attachment, an optical astronomical interferometer developed by Albert Michelson, much larger than the one he had used to measure Jupiter's satellites. Michelson was able to use the equipment to determine the precise diameter of stars, such as Betelgeuse, the first time the size of a star had ever been measured. Henry Norris Russell developed his star classification system based on observations using the Hooker.
In 1935 the silver coating used since 1917 on the Hooker 100 inch mirror was replaced with a more modern and longer lasting aluminum metallic coating that reflected 50% more light than the older silver method of coating. The newer method of coating for the telescope mirrors was first tested on the older 60 inch mirror telescope.
There are three solar telescopes, two of which are now used for astronomical research, also known as solar towers due to their construction. The 60-foot (18 m) tower telescope was completed in 1908, and the 150-foot (46 m) tower telescope was completed in 1912. The Snow solar telescope, built in 1904 is used for educational demonstrations. The telescopes are used to study helioseismology and other changes in the sun's nature.
A 24-inch (610 mm) telescope fitted with an infrared detector purchased from a military contractor was used by Eric Becklin in 1966 to determine the center of the Milky Way for the first time.In 1968, the first large-area near-IR (2.2 µm) survey of the sky was conducted by Gerry Neugebauer and Robert B. Leighton using a 62-inch (1.6 m) reflecting dish they had built.The instrument is now in the Smithsonian.