Ladd Observatory is an astronomical observatory at Brown University in Providence, Rhode Island. Dedicated in 1891, it was primarily designed for student instruction and research. The facility operated a regional timekeeping service. It was responsible for the care and calibration of clocks on campus including one at Carrie Tower and another that rang the class bell at University Hall. Meteorological observations were made there from the time the building opened using recording weather instruments. In addition to general astronomy courses it was also used for teaching civil engineering topics such as geodesy. Nautical science subjects, including celestial navigation, were taught there during both the first and second world wars. Ladd began a regular schedule of open nights for public viewing in 1930. This led to the creation of the Skyscrapers amateur astronomy society in 1932 which regularly met at Ladd. The Skyscrapers then acquired the Seagrave Observatory in 1936 which was then used as a meeting place. Amateur astronomers from the group continued to volunteer at Ladd and also participated in Brown University solar eclipse expeditions. Members constructed a Schmidt camera for the 1937 Brown eclipse expedition. Ladd was added to the National Register of Historic Places in 2000. It continues to be used by the Department of Physics at Brown for astronomy instruction. It is regularly open to the public as a science center and technology museum. It is operated as a living museum.
Construction The observatory is named for benefactor Herbert W. Ladd who offered to fund the construction in the spring of 1889. The building was designed by the Providence-based firm of Stone, Carpenter & Willson in the Classical Revival style. The selected site was the highest point in Providence at the time, on what was once known as Tintop Hill on the East Side. Construction began in May 1890 and the building was dedicated on October 21, 1891. The total cost of construction and equipping the facility in 1891 was US$40,000 (equivalent to $1,400,000 in 2025.)
Telescopes
The primary telescope is a refractor with a 12-inch (300 mm) aperture objective and focal length of 15 feet (4.6 m). The lens was figured by John Brashear following the design of Charles S. Hastings. The crown glass was made by Mantois of Paris and the flint glass by the optical works at Jena in Germany. The equatorial mount and mechanical clock drive were made by George N. Saegmuller. This telescope was used for scientific work such as lunar occultation timings to make a more precise determination of the orbit of the Moon. Instruments such as a filar micrometer could be attached to the telescope to measure binary stars. A spectroscope could also be attached to measure spectral lines. Another telescope, a 3-inch (76 mm) meridian circle instrument, also made by Saegmuller, was used for observations related to timekeeping. Similar, but smaller, instruments were used for student instruction.
Timekeeping
As a number of other observatories did in the late 19th century Ladd provided an accurate regional timekeeping service by transmitting a time signal via telegraph wire. Observations of select stars were made with the meridian circle instrument as the star transited (or crossed) the meridian. This data was then used to calibrate a high quality pendulum clock set to keep sidereal time. Calculations were then performed to convert sidereal time to local standard time. A second clock keeping standard time was equipped with a telegraphic break circuit mechanism to automatically generate the time signals. These precision clocks were known as astronomical regulators. Timekeeping instruments used at Ladd include regulators designed by Robert Molyneux, Edward Howard, Hezekiah Conant, and Sigmund Riefler.
… excerpt ends here. Continue reading the full article.
