Yerkes Observatory
Historic observatory in Williams Bay, Wisconsin, with ticketed guided tours inside the building and the Great Refractor dome, plus free arboretum grounds and trails open daily from sunrise to sunset.
Ways to visit
Space & Spaces Tour Open
Tour dates depend on the season and are posted about two months ahead.
- What you see
- Inside touryerkesobservatory.org, 2026-10-26
- How
- Timed ticket · about 1.5 hoursyerkesobservatory.org, 2026-10-26
- When
- Summer tours are typically Thursday through Monday; in spring, fall and winter the days vary by week. Arrive about 10 minutes early; guests more than 10 minutes late are not admitted.Calendar ↗yerkesobservatory.org, 2026-10-26 · yerkesobservatory.org, 2026-10-26
- Booking
- Required · opens 60 days ahead · onlineTickets are non-refundable and non-transferable; rescheduling may be possible with a week's notice.Book ↗yerkesobservatory.org, 2026-10-26
- Cost
- Not stated on the official pageNo ticket price is given; no cash accepted, cards and mobile pay only.yerkesobservatory.org, 2026-10-26
- Requirements
- Minimum age: 5+. Ages 5+.
- Fitness and accessibility: Yes. Involves standing, walking, climbing staircases and small spaces; not wheelchair accessible.
Arboretum grounds and trails Open
May close for private events.
- What you see
- Groundsyerkesobservatory.org, 2026-10-26
- How
- Walk inyerkesobservatory.org, 2026-10-26
- When
- MonTueWedThuFriSatSunOpen daily from sunrise to sunset; the building itself is not open on this basis.Closed: Occasional private eventsyerkesobservatory.org, 2026-10-26
- Booking
- Not required · same day possibleNo ticket needed for the grounds.yerkesobservatory.org, 2026-10-26
- Cost
- FreeFree to explore.yerkesobservatory.org, 2026-10-26
- Requirements
- Photography: Yes. Photo sessions on the grounds need advance permission; no photo shoots inside the building.
About
Yerkes Observatory houses the Great Refractor, described by the observatory as the world's largest refracting telescope. The building can be entered only on ticketed tours and events, with tickets released about two months ahead and tours often selling out. The surrounding arboretum and trails are open without a ticket from sunrise to sunset unless a private event is on. Night-sky viewing programs and seasonal events such as Frostlights also run, and prices are listed only on the ticketing system.
Getting there
Williams Bay, WI
Tour check-in is at the south (main) entrance of the building, about 10 minutes before the tour time.
The pin marks the site itself, not necessarily the entrance (42.57028, -88.55667). Show on our map · Google Maps · Apple Maps
Yerkes Observatory (phones answered Mon-Fri 9-3): 262-245-5555 · info@yerkesobservatory.org
Last checked 2026-10-26. Sources are listed below.
Sources
- yerkesobservatory.org · official page · read 2026-10-26For: name
- wikidata.org/wiki/Special:EntityData/Q1431… · Wikidata · read 2026-10-26For: location
- yerkesobservatory.org/tour-and-event-tickets/ · official page · read 2026-10-26For: phone and email; Space & Spaces Tour: open or closed; Director's Hidden Spaces tour: open or closed; Director's Hidden Spaces tour: what you see; Director's Hidden Spaces tour: cost; Director's Hidden Spaces tour: requirements; Arboretum grounds and trails: kind of visit; Arboretum grounds and trails: booking
- yerkesobservatory.org/tours-and-events/space-spaces… · official page · read 2026-10-26For: Space & Spaces Tour: what you see; Space & Spaces Tour: cost; Space & Spaces Tour: requirements
- yerkesobservatory.org/faqs/ · official page · read 2026-10-26For: Space & Spaces Tour: kind of visit; Space & Spaces Tour: days and hours; Space & Spaces Tour: booking; Director's Hidden Spaces tour: kind of visit; Director's Hidden Spaces tour: days and hours; Director's Hidden Spaces tour: booking; Arboretum grounds and trails: open or closed; Arboretum grounds and trails: what you see; Arboretum grounds and trails: days and hours; Arboretum grounds and trails: cost; Arboretum grounds and trails: requirements
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