Yerkes Observatory is open to the public from 9:45 a.m. to 1:30 p.m. every Saturday throughout the year excluding Christmas and New Year's Day. Our expert, engaging and entertaining tour guides provide a fascinating program covering the Observatory's history, architectural detail, astronomical research, and a look inside the 90-foot dome at the 40-inch refractor, still the largest lens-type telescope in the world. Guided tours begin at 10:15 a.m., 11:15 a.m., and 12:15 p.m. and last 45 to 50 minutes. We do not accept reservations. A suggested donation of $8 per person is requested to support our public programs which are intended for families and small groups. The interior of the 90-foot dome is unheated, so dress appropriately on the day of your visit for outdoor temperatures. For more information about all Yerkes tour programs call 262-245-5555, extension 825, weekdays between 9:00 a.m. and 4:00 p.m. Tour questions can also be emailed to firstname.lastname@example.org.