The University of Chicago

373 W. Geneva St, Williams Bay WI 53191 (Latitude 42 34.2, Longitude -88 33.4)
Look Through a Large Telescope at the Moon, Planets, Galaxies, the Milky Way, Nebulae, Star Clusters and More at Yerkes Observatory!

From season to season the evening sky changes slowly and reveals many different celestial wonders visible with, and without, optical aid. Every month during the year, on select weekday and weekend evenings, Yerkes Observatory offers observing sessions with our 40-inch diameter refractor telescope, the largest lens telescope and the third largest telescope available for public viewing in the world, and with our 24-inch diameter reflector telescope, weather permitting, for participants who are age 10 and older.

Both telescopes were formerly used for astronomical research and are now available for public observing opportunities. For most participants either one will likely be the largest telescope they will have access to for viewing the night sky in detail. The difference between the views presented by the refractor vs. the reflector is dramatic, though. For an affordable, general night sky tour and introduction to astronomy we suggest reservations with the 24-inch reflector. For a truly once-in-a-lifetime and unforgettable observing experience using the same telescope as some very famous astronomers over the past century, we suggest the 40-inch refractor.

We are currently accepting observing reservations for the following dates through July 2018 with the 40-inch refractor:

June 18. Programs begin at 9:30 pm.
July 1, 3, 5, 6, 9, 10, 11, 16, 18, 19, 29, 30 and 31. Programs begin at 9:15 pm.

40-inch refractor programs last about 2 to 2-1/2 hours.

August public observing dates, including Labor Day weekend, with the 40-inch refractor will be posted here by June 22.
Please read the note below concerning suspension of the large telescope programs at Yerkes after September 2.

We are currently accepting observing reservations for the following dates in June 2018 with the 24-inch reflector:

June 17, 18 and 19. Programs begin at 9:15 pm

24-inch reflector programs last about 90 minutes to 2 hours.

July dates for public viewing with the 24-inch reflector will be posted here by June 22, and August dates (including Labor Day weekend) will be posted here by July 20.

The public observing programs with the 24-inch reflector and 40-inch refractor telescopes at Yerkes will be temporarily suspended after Sunday, September 2, 2018. No public observing sessions will be available after that date until further notice.

Public observing events with the large telescopes at Yerkes are very popular and often sell out quickly. Space on each tour is limited and subject to availability. Scheduled sessions can be canceled due to adverse weather conditions (clouds, rain, storms or high winds) and, in rare circumstances, Observatory event conflicts that arise after public observing dates have been announced or due to equipment problems.

The program costs are $100 per person for the 40-inch refractor program and $37.50 per person for the 24-inch reflector program, payable the evening of the event by cash, VISA or Mastercard. Reservations are required and can be made by email only at Please use this email address for reservations and questions concerning the telescope programs only.

IMPORTANT: Reservation requests MUST include the following information:

  • The name of the group organizer.
  • An email address the group organizer can access the day of the event.
  • The group organizer’s cell phone number.
  • The number of people in the party.
  • The telescope program in which the group wished to participate (""reflector" or "refractor").

Reservation requests will be answered by an Observatory representative via email with additional information and instructions pertinent to your visit. Confirmations are sent periodically throughout the week so please be patient - we are a small staff with many duties at Yerkes.

For information and questions about other Yerkes tours please email (monitored seven days a week) or call us at 262-245-5555, ext. 825, 9:00 am to 4:00 pm, weekdays. The Observatory office is not staffed outside of these hours or on weekends.

Scheduled event dates are removed from the above listings as quickly as possible after each sells out. During late spring and early summer evenings from the dark sky environment at Yerkes you may see superb views of the moon, constellations, hundreds of stars, star clusters, nebulae, galaxies, the Milky Way, an occasional meteor and artificial satellites. Binoculars can enhance your viewing experience, but are not necessary.

For information about regularly scheduled Saturday tours, weekday tours, and other events, please click here.