Free Observatory Nights in Illinois

Illinois has been looking up for a long time, and it owns one of the great telescopes in American astronomy to prove it. On the roof of Northwestern’s Dearborn Observatory in Evanston sits an 18.5-inch Alvan Clark refractor that, when its lens was finished in 1862, was the largest refracting telescope in the world — and it was through that very lens, still being tested, that Alvan Graham Clark first glimpsed the faint white-dwarf companion of Sirius, a star nobody had ever seen. You can put your own eye to it, for free, on a Friday night. From the Chicago lakefront out to the western suburbs and all the way down to Carbondale, Illinois opens real telescopes to the public on a schedule you can plan around, and it costs nothing.

Illinois has a handful of public observatories and astronomy clubs that open free to the public on a schedule you can plan around, run by three universities, a downstate campus, and two of the state’s big amateur clubs. They stretch from Evanston on the north shore across the suburbs and central prairie to Carbondale in the far south. My own telescope is a 10-inch; the 18.5-inch Clark near Chicago gathers more than three times the light mine does, and you can look through a piece of astronomical history without paying a dime. Here is where the free ones are, which night each opens, and how not to waste the drive. (The Adler Planetarium’s lakefront observatory is a separate case worth knowing about — it gets its own note near the end.)

Dearborn Observatory, Northwestern, Evanston: the historic refractor that found Sirius B, free every Friday

On the Northwestern campus in Evanston, just up from the Lake Michigan shore, the Dearborn Observatory houses one of the most storied telescopes in the country: an 18.5-inch Alvan Clark refractor that was the largest in the world when its lens was completed in 1862, and the instrument through which Alvan Graham Clark first spotted the companion of Sirius, the faint white dwarf now called Sirius B. Built for it in 1889, the domed observatory still opens that telescope to the public, for free, on Friday nights.

The tours run every Friday, year-round, in two seasonal blocks: from April through September the sessions are 9 to 11 p.m., and from October through March they are 8 to 10 p.m. The one wrinkle on this page: the first hour is reservation-only (book it online through the observatory’s site), and the second hour is walk-up, no reservation needed — so if the reserved slots are full, just come for the later hour. Two cautions the observatory makes itself: the dome is neither heated nor air-conditioned, so dress for the outside temperature, and reaching the telescope means climbing several flights of stairs, so it is not wheelchair-accessible. For anyone in the Chicago metro, this is the marquee free night in the state.

University of Illinois Observatory, Urbana: a 128-year-old refractor, free the second Friday

In the middle of the state, the University of Illinois opens its historic campus Observatory in Urbana to the public free of charge, and its open houses run, in the department’s own words, “the second Friday of the month, for about two/three hours” during the fall and spring semesters. The centerpiece is the original 12-inch refracting telescope, more than 128 years old, alongside several smaller scopes staff and students set up for the crowd.

Timing shifts with the season: spring, summer and fall sessions usually run 8 to 10 p.m., and winter ones 7 to 9 p.m. It is free and there is no reservation. And here is the nicest touch — the observatory says that even if the sky clouds over, “we’ll still be there giving tours of the observatory” and talking through its history, so a cloudy night is not a wasted trip. It sits at 901 S. Mathews Avenue with free parking in the lot just east. For Champaign-Urbana and central Illinois, this is the free night to circle.

Davis Hall Observatory, Northern Illinois University, DeKalb: free every Wednesday

West of the Chicago suburbs, in DeKalb, Northern Illinois University’s Department of Physics opens its Davis Hall Observatory to the public — and it puts the deal plainly: “Public viewing is free and open to everyone,” with the observatory open from 8 to 10 p.m. on Wednesdays, weather permitting. No reservation.

The observatory runs a Celestron 14-inch Schmidt-Cassegrain and a TeleVue 85 mm refractor, a nice pairing — the big scope for planets and deep-sky objects, the small refractor for wide, bright views of the Moon and star fields. Because a Wednesday night in northern Illinois is a coin-flip for clouds, the department posts weather and observing conditions on its Facebook page, so check that before you make the drive. For DeKalb, Sycamore and the western edge of the metro, it’s the most reliable standing free eyepiece around.

Naperville Astronomical Association: free public nights all year in the western suburbs

Out in the western suburbs, the Naperville Astronomical Association — a 501(c)(3) club — hosts, in its own words, “free Public Nights at our Astronomy Education Center all year ’round.” The center holds two observatories: the Glen D. Riley Observatory, built in 1973, for looking through the eyepiece, and the DuPage Valley Observatory, added in 2003 and fitted with a live video-imaging system that puts faint galaxies and nebulae on a screen for the whole group.

The public nights run on scheduled evenings across the year rather than a fixed weekly night, so check the club’s calendar for the next date before you head out. Because it’s a club event, the members are there because they want to show you the sky — and the video observatory is a different way to see the deep sky than a plain eyepiece, worth catching at least once. For Naperville, Aurora and the DuPage County suburbs, this is the free night to build around.

Fox Valley Astronomical Society, Peck Farm Park, Geneva: a free monthly star party

Along the Fox River in Geneva, the Fox Valley Astronomical Society, a club that has been at it since 1944, “is proud to sponsor a free monthly public star party” at Peck Farm Park. The evening starts with a short optional presentation in the Meeting Barn, and then members roll their telescopes out into the parking lot and give visitors a tour of the planets, the Moon and whatever deep-sky objects the season offers — and you’re welcome to bring your own scope, too.

The star parties run 7 to 10 p.m., once a month, at Peck Farm Park, 4038 Kaneville Road in Geneva. Dates follow the club’s own calendar and the observing season, so check the society’s site for the next one before you drive out. For the Fox Valley — Geneva, St. Charles, Batavia and Aurora — it’s a relaxed, welcoming night where nobody minds a beginner’s questions.

Southern Illinois University, Carbondale: free public astronomy in the deep south of the state

Down in Carbondale, near the southern tip of Illinois, SIU Physics hosts free monthly public astronomy observations in partnership with the Astronomical Association of Southern Illinois. The main instrument is a computer-guided 14-inch Meade LX600, backed up by Celestron 8-inch Schmidt-Cassegrains, a Coronado solar telescope for daytime sun-watching, and a 105 mm refractor.

The sessions run roughly monthly and are timed to when the sky is worth showing, but the exact dates are posted rather than fixed to a weekly night, so check the department’s events page or its Facebook before you go. Far southern Illinois has darker skies than the Chicago half of the state — this stretch sat under the path of two total solar eclipses in recent years — so for Carbondale, Marion and the deep south, this is the free eyepiece to find.

The Adler, and the one that’s actually in Wisconsin

Two famous names come up that aren’t among the six above. The Adler Planetarium on the Chicago lakefront runs the largest publicly accessible telescope in the city — its Doane Observatory — and opens it to the public for viewing on clear Wednesday nights through its “’Scopes at the Adler” program; the museum’s daytime telescope terrace, by contrast, is included with paid admission. The night observing is weather- and staff-dependent and the schedule shifts, so if you want the Adler, check its own page and Facebook group for the current dates rather than just showing up. And the Yerkes Observatory, with its own record-holding 40-inch Clark refractor — the largest refractor ever built for research — is often lumped in with Chicago because the University of Chicago built it, but it sits across the state line in Williams Bay, Wisconsin, so it doesn’t belong on an Illinois list. Both are worth a trip; neither is one of the state’s six standing free nights.

What a public observatory night is actually like

None of these is a planetarium show. You’re visiting a working telescope run by staff, students or volunteers who show up because they like showing people the sky, and the evening has a rhythm worth knowing before you arrive.

• You’ll wait, then look, then wait again. A dome holds a dozen or so people and the telescope shows one object at a time, so expect a couple of minutes at the eyepiece per target. Ask the operator what’s next; it’s their favorite question.
• Red light only. Every site here runs on red light after dark to protect night vision. Bring a red flashlight (our red flashlight guide has picks from $10) and dim your phone before you walk up — a white screen in a dark dome is the one sure way to annoy everyone around you.
• Dress warmer than you think. Observatory domes sit at the outside air temperature, and Illinois clears off coldest on exactly the nights worth going — a crisp, transparent winter sky. A hat and a layer past what the day called for are the difference between staying two hours and leaving after twenty minutes.
• It cancels for cloud, and that’s a feature. A telescope aimed through overcast shows nothing, so every site above decides that evening. Check the status line, the page, or the club’s Facebook before you leave — and don’t take a cancellation personally, it just means the next clear night will be worth it.
• The Moon is a target, not an enemy. Dark-sky trips want a new Moon; observatory nights are the opposite. A first-quarter Moon through a big telescope is the best thing on the menu, its craters lit from the side. Our Moon-observing guide explains why the terminator, not the full Moon, is where the detail lives.

What you’ll see, by season

The planets set the calendar. Saturn is the reason most people say “oh” out loud at the eyepiece, and it’s an evening object from late summer through the end of the year; our Saturn guide has the dates. Jupiter follows it into autumn and winter, its four bright moons rearranged every night. Summer brings the Ring Nebula and the great globular cluster in Hercules; autumn the Andromeda Galaxy, a soft oval even from a lit suburb but the light of a trillion suns that left two and a half million years ago; winter the Orion Nebula, spectacular in any aperture. Illinois’s clearest, steadiest nights come in the cold months, when the summer haze is gone — bundle up, because that crisp January sky is when a big telescope earns its dome. The Moon is up about half the nights of any month, and through these telescopes it never gets old.

If the eyepiece gets you

It does that. Half the people who own a telescope bought one after a night like this. The next step isn’t an 18.5-inch; it’s the beginner’s guide to learning the sky with your eyes, then a pair of astronomy binoculars or one of our beginner telescope picks, most of which cost less than a nice dinner out. When you want the sky itself and not just the objects, Illinois has one properly dark refuge inside its borders — the Middle Fork River Forest Preserve near Champaign, the state’s first and only certified International Dark Sky Park, a two-hour drive from Chicago; our best national parks for stargazing guide has the darkest skies across the country. And if you’re reading this from another state, the New York, Pennsylvania, New Jersey, California, Texas and Florida lists do the same thing there. Do the free night first. Zero dollars and someone else’s telescope is the best deal in astronomy.