{"nrhp_refnum":"89002466","name":"University of Illinois Observatory","other_names":[],"category":"building","location":{"address":"901 S. Mathews Ave.","address_restricted":false,"city":"Urbana","county":"Champaign County","state":"IL","lat":40.10520989300005,"lon":-88.22618281099994,"geom_source":"nps_gis"},"listed_date":"1989-12-20","is_nhl":true,"nhl_designated_date":"1989-12-20","areas_of_significance":["Engineering","Education","Science"],"significance_levels":["national"],"summary":{"what_it_is":"A one-story, T-plan brick astronomical observatory with a domed tower at 901 South Mathews Avenue, Urbana, Illinois, built in 1896 to designs by architect Charles A. Gunn.","why_significant":"The nomination argues the observatory is significant for the development of the selenium photoelectric cell and later photoelectric photometry by director Joel Stebbins between 1907 and 1922. Using the 12-inch refractor, this work made photoelectric measurement of stellar magnitudes the standard technique in astronomy. The research replaced visual and photographic methods with a quantifiable science.","narrative":"Built in 1896 on a grassy knoll in Urbana, the University of Illinois Observatory is a one-story, T-plan building of buff Roman brick with limestone lintels and sills. An octagonal tower, which becomes round higher up, carries a copper-roofed dome housing a 12-inch Warner and Swasey refractor on a brick pier that extends to bedrock. Charles A. Gunn was the architect, and Bevis and Company the contractor. Additions in 1956 and 1966 used light cream-colored brick and copied the original details. The building matters for work done between 1907 and 1922, when director Joel Stebbins and physicist F.C. Brown attached a selenium cell to the refractor and recorded a light curve of the moon. Later work with Jacob Kunz's improved cells produced precise light curves of eclipsing stars. This research made photoelectric photometry the standard way to measure stellar brightness. The basement and dome remain in astronomy use, and the other rooms serve as university offices.","period_of_significance":"1907-1922","architect_builder":"Charles Gunn (architect); Bevis and Company of Urbana (general contractor)","architectural_style":"No style","criteria":[],"status_note":"The basement and dome with the 12-inch refractor are still used by the university astronomy department; the remaining rooms house administrative offices. Additions were built in 1956 and 1966.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:35.861239-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/0/8915/28891500/content/electronic-records/rg-079/NPS_IL/89002466_NHL.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/89002466/b24df7403e-800.webp","url_1600":"https://nationalhistoricalregister.com/media/89002466/b24df7403e-1600.webp","licence":"CC BY 2.0","author":null,"credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Champaign-Urbana_area_IMG_1138.jpg\" rel=\"noopener\">Unknown author</a>, <a href=\"https://creativecommons.org/licenses/by/2.0\" rel=\"license noopener\">CC BY 2.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Champaign-Urbana_area_IMG_1138.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28891500","wikipedia":"https://en.wikipedia.org/wiki/Astronomical_Observatory_(University_of_Illinois_Urbana-Champaign)","wikidata":"https://www.wikidata.org/wiki/Q3348346"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/champaign-county/university-of-illinois-observatory-89002466/"}