University of Illinois Observatory
Why it's listed
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.
Significance in brief: 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.
Machine-generated summary. This summary was generated by a language model from the official nomination document and has not been reviewed line by line by an editor. It may contain errors. Check the source document before relying on any detail. Source: nomination document (PDF) · National Archives catalog entry. NRHP reference 89002466, listed December 20, 1989. Summary generated October 2026 (model claude-sonnet-5-5, prompt v1.0-2026-10-29, confidence high).
Key facts
| Address | 901 S. Mathews Ave., Urbana |
|---|---|
| County | Champaign County |
| Listed | December 20, 1989 |
| Reference number | 89002466 |
| Resource type | Building |
| Period of significance | 1907-1922 |
| Architect / builder | Charles Gunn (architect); Bevis and Company of Urbana (general contractor) |
| Architectural style | No style |
| Areas of significance | Engineering, Education, Science |
| Level of significance | National |
| National Historic Landmark | Yes, designated December 20, 1989 |
| Status (as stated in the nomination) | 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. |
| Acreage | 0.9 |
| Coordinates | 40.10521, -88.22618 (NPS GIS) |
What listing means for this property
For a publicly owned building or structure, listing mainly matters when federal funds, permits or licences are involved: projects then go through Section 106 review so effects on the property are considered. Listing also strengthens applications for preservation grants and, for leased income-producing uses, can enable the federal rehabilitation tax credit.
General information, not legal or tax advice. Rules change; confirm with your State Historic Preservation Office or a qualified adviser.
Sources and further reading
- National Park Service, National Register of Historic Places database (snapshot May 2026), reference 89002466.
- Nomination form (PDF, National Archives) — catalog entry
- Wikipedia article (used for cross-checking only; text not reproduced here)
- Wikidata Q3348346
- This listing as JSON
Last updated October 2026. Found an error? See the editorial policy for how to report it.