The , or Manuel Foster Observatory, is an astronomical observatory constructed on Cerro San Cristóbal near Santiago, Chile in 1903. This site was originally known as the D. O. Mills Observatory after the philanthropist Darius Ogden Mills. It was built as an offshoot of the Lick Observatory to observe stars in the southern hemisphere, and, under the direction of the American astronomer W. W. Campbell, was used in an extensive project to determine the apex of the Sun's motion through space.
The initial funding for the project financed operations for a two year period. Because Campbell had been seriously injured, the expedition was headed up by his assistant, William H. Wright. After setting up the telescope and the observation dome, the instrument quality was found to be satisfactory and operations began late in 1903. A total of 800 spectrograms had been successfully collected by October 1905. Heber D. Curtis took over operations in March 1906, and new financing from Mills allowed improvements to the observatory. Using the data collected from this observatory, Campbell completed his study on the motion of the Sun in 1926. With added funding, operations continued at the observatory until 1928, when it was purchased by Chilean lawyer Manuel Foster Recabarren for the Universidad Católica de Chile and transferred to their control.
The observatory is located in the Santiago Metropolitan Park and became a national monument in 2010. The main telescope is a cassegrain reflector with a aperture and an equatorial mount. This instrument is housed inside a rotating dome.
History
In 1897, the astronomer William Wallace Campbell, assisted by William H. Wright, began a program of measuring the radial velocity of all stars in the northern hemisphere having an apparent visual magnitude of 5.51 or brighter. This task was facilitated by the newly installed Mills spectrograph, which was attached to the telescope at the Lick Observatory. This instrument was specifically designed for photographing stellar spectra, and was made possible by a grant from the banker Darius O. Mills. It saw first use in May 1895 and proved highly successful, improving accuracy by an order of magnitude over previous instruments. The design included three prisms and an iron arc comparison system. However, there were flexure and light loss issues that limited its capabilities. By 1903, an improved design allowed measurements of stars at fainter magnitudes.
In 1894 Campbell first recognized the need for similar radial velocity measurements of stars in the Southern Hemisphere. This would allow a more complete investigation of the Solar System's motion with respect to the neighboring stars. The director of the Lick observatory, James Edward Keeler, died on August 12, 1900, and Campbell was named to succeed him as of January 1, 1901. When Campbell brought the need for a southern observatory to the attention of D. O. Mills, the banker agreed to finance this expedition. In sum, an amount of $26,075 would be provided, to cover the cost of instruments, building construction, salaries, travel expenses, and supplies for this two year expedition. This is . The plan was for the completed observatory to be a much less costly duplicate of the spectroscopic capabilities of the instruments used for the northern survey. The resulting cost was one eighteenth the cost of the Lick observatory main telescope. For the observatory location, Campbell initially considered possible sites in Australia. However, climate records and the reports from other astronomers indicated that Chile would be a better site. He finally settled on placing it in the vicinity of the Chilean capital of Santiago, so that supplies and living quarters would be readily available.