Lowell Observatory’s 21-inch Telescope Delivering Long-Term Results

NASA-Funded Program Still Gathering Outer Planets’ Light Over 50 Years Later

Flagstaff, Ariz.– A unique 21-inch telescope housed in a 1920s stone building on Lowell Observatory’s Mars Hill campus continues to serve as astronomer Wes Lockwood’s main telescope in a project originally aimed a half century ago atmonitoring solar irradiance variability. After the arrival of astronomer Harold L. Johnson in 1952, the telescope was used to “train on the Sun’s light reflected from planets Uranus and Neptune.” Over half a century later, Lowell’s 21-inch remains productive in monitoring the brightness of Uranus and Neptune against a reference set of precisely measured sunlike comparison stars, aprogram in its 52nd year.

“We never expected this work would go on for a half a century,” said Wes Lockwood, Lowell Observatory Astronomer. “But, once we realized we had a unique product whose value increases the longer it goes on, it seemed crazy to quit.”

The telescope was installed in 1953 on a homemade mounting in a stone building with a fully retractable roof. Although no solar variations were ever detected in this original quixotic quest of monitoring the Sun’s light — and indeed could not have been detected given the Sun’s now well-known, miniscule 0.1 percent variation over the solar cycle — this 21-inch telescope has made it possible to indirectly approach the question by measuring, more precisely than elsewhere, and for a longer interval, the tinyfluctuations of stars that closely resemble the Sun.

During this program, the telescope has also hosted many astronomers over the years and been used in observations for 150 refereed journal publications. It has attracted significant funding, as well. Over $3,500,000 (2005 dollars since 1970) has been granted for research with this 21-inch from the National Science Foundation, NASA, and the U.S. Air Force.

The 21-inch was first used for Johnson’s seminal work definingstandards for the UBV photometricsystem and measurements of color-magnitude diagrams for nearby open clusters. Since then, Lowell’s 21-inch has supported a steady stream of variable star work by Jerzykiewicz; early interstellar polarization measurements by Serkowski and Krzeminski; drift scans of the Andromeda Galaxy by de Vaucouleurs; characterization of the variability of sunlike stars by Jerzykiewicz and Serkowski; and a modern reincarnation of the same project with higher precision by Lowell Observatory’s Lockwood and Skiff, plus 50-plus-year lightcurves ofUranus and Neptune and a complete 29.5-year seasonal lightcurve of Saturn’s moon, Titan.Byproducts from the astronomical datainclude a decades-long time series of atmospheric extinction measurements and a record of sky brightness above Mars Hill that aided the Observatory’s efforts in dark sky preservation in Flagstaff, the first International Dark Sky City.

“Working with a manually slewed telescope on 1,200 nights gives one a tremendous appreciation of the richness of the sky,” said Brian Skiff, Lowell Observatory Research Assistant.

With fully robotic photometric telescopes now taking over much of the stellar research begun with Lowell’s 21-inch telescope, the future of this historic workhorse is in question. Nevertheless, it continues to fill a niche not easily satisfied by more sophisticated, modern instrumentation.

Lockwood and Jerzykiewicz’s study, “Photometric variability of Uranus and Neptune 1950-2004,” is in press in Icarus. Support is provided by NASA. Lockwood presents these results during the 207th meeting of the American Astronomical Society in Washington, DC.