Skip to main content

Dearborn Observatory Records

Identifier: 29/2
The records of the Dearborn Observatory fill fifty-four boxes and thirteen oversize folders. The records span the years 1863-1967, although the bulk dates from 1863-1941. The records consist almost entirely of observational data gathered by astronomers using Dearborn's 18½ inch refracting telescope or its meridian circle, calculations performed on the data, and the results of such investigations. Six folders of clippings, reports, and miscellaneous correspondence precede the observational records and two boxes of visitor's registers and material relating to the observatory's library follow the observational records.

The observational records created during the directorships of Truman Safford, Elias Colbert and George W. Hough were entered in notebooks, two hundred and five of which survive. Initially all observations were entered sequentially in notebooks. Separate records were kept for the equatorial (the 181/2 inch refractor) and the meridian circle. As various observational programs became more extensive, separate notebooks were created to record the results of the respective programs. The early notebooks are arranged as either equatorial or meridian circle observations and chronologically within oversize folders these categories, while later notebooks are grouped according to the subject of the observation.

The records include five and a half boxes, containing fifty-five volumes, of general observations made with the equatorial spanning the years 1863-1908 and the directorships of Safford, Colbert, and Hough. The majority of the observations were made by the three directors, although S.W. Burnham and several assistant astronomers contributed to the observations. The volumes include records of planetary studies, with observations of Jupiter, Uranus, and Neptune being the most numerous; stellar observations concerned primarily with fixing the exact locations and magnitudes of various stars; observations made to establish precise longitudes and latitudes; and observations of other celestial objects and events, such as asteroids, comets, and eclipses. In many cases the recorded data is not clearly identified, thus limiting its usefulness to all but experienced astronomers. For the most part, data recorded in the equatorial notebooks was not derived from systematic research projects and no narratives exist detailing the nature of the observations for the non-scientist.

Five boxes of meridian circle observations spanning the years 1868-1908 follow the general equatorial observations. The meridian circle was an instrument developed in the 18th and 19th centuries to establish the precise positions and proper motions of all bright stars. The planets, Moon, and Sun were then studied in relation to the meridian observations. The sixty volumes of meridian circle observations are arranged in categories according to the types of observations recorded as indicated in the titles of the volumes (Zero Stars, Great Catalogue, Working Lists, And general observations) and chronologically within each category.

Several worldwide cataloging projects were begun in the mid-nineteenth century. The Dearborn Observatory participated in a project directed by the Astronomische Gesellschaft in Berlin. Volumes of records document Dearborn's participation from 1868 until 1871 when the Chicago Fire curtailed research. Systematic meridian circle observations began again in 1879.

Notebooks detailing more specialized observations include seventeen volumes of occultation studies concerning the blocking of light from celestial bodies by other bodies, two boxes and one oversize folder of observations of Jupiter (see also the George Washington Hough Papers, Series 29/1), seven volumes concerning the Moon's parallax, and two volumes concerning a project to precisely measure the longitude, latitude and sizes of the Great Lakes. Following the volumes that record clearly identified specialized observations are three and one-half boxes of miscellaneous observations dating from 1863-1908. Some of the volumes have indications of their content, such as planets, zenith distance and Bradley stars. However, the majority oversize folders merely record observations and would require expertise in astronomy to be useful. The miscellaneous observations are arranged chronologically.

In addition to observational records from the period 1863-1908, the records include two boxes and three oversize folders of data pertaining to instruments used in the Observatory. The bulk of this data relates to Dearborn's standard time service, recorded in twenty-three volumes spanning the years 1869-1908. Also included are three oversize folders of meteorological data produced by Dearborn's printing barometer.

Following Hough's death, observational data gathered at Dearborn was no longer recorded in notebooks. With the directorship of Philip Fox, Dearborn's astronomical program was expanded, with the result that much of the actual observational work was done by graduate students. Fox instituted a regular reporting format that resulted in more clearly labeled records. Each sheet of observations records the observer's name, the date and the nature of the observation.

The records include one box of Fox's spectroheliograms that detail the sun's features by photographing it with monochromatic light. The bulk of the observational data from Fox's tenure concerns the stellar parallax measurement project.. Parallax refers to the apparent displacement in direction of an object when seen from two different, points not on a straight line with the object. The differing perspectives of a given star are created by observing it over a period of time as the earth moves in its orbit. Knowing the parallax for a star allows the astronomer to fix its position precisely by correcting for the parallax effect.

The records also include five boxes of parallax measurements taken between 1916 and 1929. Arrangement is chronological according to the date of the first observation made for a given star, even though in many instances a star was re-observed several times over as many as twelve years before a true value for its parallax could be calculated. The records indicate the identification of the star under observation by its name or its star catalog number, the name of the observer, the time and date of the observation, the observational data and the calculations resulting in an accurate parallax value.

In addition to the parallax measurements, there are one and one half boxes of reduction calculations which represent the determinations of the true positions of stars when corrected for parallax and proper motion error. (See also the Records of the Annals of the Dearborn Observatory, Series 29/3. Volume 3 of the Annals published Fox's parallax measurements and other volumes include further information on the stellar parallax project.)

During the directorship of Oliver Lee, several large projects were carried out. The records include one box of miscellaneous observations and five oversize folders of time clock records, 1933 to 1934. Also included are six boxes of records concerning Lee's observations of the asteroid Eros in 1930-1931. Eros' orbit brings it closer to the earth than any other large heavenly body besides the Moon. In 1931, Eros came within 13.8 million miles of the Earth, making it the subject of intense astronomical interest. The gravitational force of a large body passing so closely made it possible to more precisely measure the Mass of the Earth and the Moon, in addition to making close up general observations of the large asteroid itself. The records pertain to the measurements of the effects of the Earth on Eros and the changes caused in observed parallax. General observations of the character of Eros are also included.

The bulk of the observations during Lee's directorship document his Red Star Project from 1931-1941. Fourteen boxes detail Lee's study of huge-forming, red stars. The bulk of the data is arranged numerically according to folder numbers assigned by Lee, with the remainder arranged by photographic plate numbers or star name. The data pertains to the magnitude, or brightness of selected red stars and changes in their magnitude.

The only observational records from Hynek's directorship are two oversize folders of charts recording magnitudes of stars. The charts are not clearly labeled and require a sophisticated knowledge of astronomy to be useful. In addition, two oversize folders of miscellaneous observations and mechanical drawings of scientific instruments follow the main body of the records.


  • 1863-1967


Conditions Governing Access

This collection is stored off-site and requires 48 hours advance notice for retrieval. Please contact the Northwestern University Archives at or 847-491-3136 for more information or to schedule an appointment to view the collection.


59.00 Boxes


Records of Dearborn Observatory, built in 1865 by the Chicago Astronomical Society and the University of Chicago and in 1889 moved to Northwestern University's Evanston campus. Dearborn Observatory was a significant contributor in the area of double star research. The records consist almost entirely of observational data gathered by astronomers using Dearborn's 18-1/2 inch refracting telescope or its meridian circle, calculations performed on the data, and the results of such investigations.


The observations are grouped into the following major groups: equatorial (arranged by date); meridian circle (arranged by date); transits of meridian (arranged by date); occultations (arranged by date); Jupiter (arranged by date); double stars (arranged by date); instrument; parallax measurements (arranged by date); time set reductions (arranged by date); time clock observations (arranged by date); Eros observations (arranged by date); redstar (organized by project number). Interspersed among these are several groups of miscellaneous observations, and many minor groups (typically arranged by date) and other topics.

Method of Acquisition

The Records of the Dearborn Observatory were transferred to the University Archives prior to June, 1974 as Accession #74-65.

Separated Materials

One-half cubic foot of faculty publications was transferred to the Archives' Biographical Files; one cubic foot of Bulletins of the Royal Astronomical Observatory was sent to the Library's Gifts and Exchange Department; three cubic feet of material were separated as the George Washington Hough Papers (Series 29/1); one cubic foot was separated as the papers of Truman Safford and Philip Fox; two cubic feet were separated as the records of the Annals of the Dearborn Observatory.

Processing Information

Thomas J. Dorst, July, 1982


Guide to the Dearborn Observatory Records
Thomas J. Dorst
Description rules
Describing Archives: A Content Standard

Repository Details

Part of the Northwestern University Archives Repository

Deering Library, Level 3
1970 Campus Dr.
Evanston IL 60208-2300 US