Sommers-Bausch Observatory (SBO) on the University of Colorado Boulder campus is operated by the Department of Astrophysical and Planetary Sciences (APS) to provide observational experience for undergraduate students and hands-on training in astronomical observations and instrumentation for departmental majors and graduate students, as well as lab space for the APS departments labratory classes.


The University of Colorado Boulder, Colorado’s flagship university, honors and recognizes the many contributions of Indigenous peoples in our state. CU Boulder acknowledges that it is located on the traditional territories and ancestral homelands of the Cheyenne, Arapaho, Ute and many other Native American nations. Their forced removal from these territories has caused devastating and lasting impacts. While the University of Colorado Boulder can never undo or rectify the devastation wrought on Indigenous peoples, we commit to improving and enhancing engagement with Indigenous peoples and issues locally and globally.



  • Latitude: +40 deg 00' 13.36" (40.00371 degrees North)
  • Longitude: -105 deg 15' 46.84" (105.2630 degrees West)
  • Altitude: 1653 meters (5423 feet ASL)

Geographic Latitude

The observatory is slightly over 1/4 mile (1,357 feet) north of the Earth's 40th Parallel of Latitude (the street named Baseline which runs east-west through the southern portion of the city of Boulder).

Observatory Code

Sommers-Bausch Observatory is listed with the IAU and MPC with an Observatory Code of 463. SBO users who file a report with the International Astronomical Union or its Minor Planet Center should include the code for identification.

Sidereal Time

The Observatory lies 7 hours, 1 minute, 3.24 seconds of time west of the Prime Meridian, hence our Local Sidereal Time trails that of Greenwich England by 7h 1m 3s.

Mean Solar Time

Our Local Mean Solar Time lags behind Mountain Standard Time (mean time at the 105th meridian) by 63 seconds. Subtract 1 minute and 3 seconds from the civil timezone MST to obtain the Local Mean Solar Time at SBO.

Local Apparent Solar Time

Sundial time is the true solar time at our location equal to the hour angle of the Sun (plus 12 hours since LAST begins at midnight rather than noontime). From your adjustment for Mean Solar Time, subtract the appropriate value from the Equation of Time chart to obtain the SBO Local Apparent Solar Time.