The Adler Planetarium’s Doane Observatory is pretty special. It is home to the largest telescope available to the public in the Chicagoland area! That means that guests get to see the sharpest and brightest view of our universe that Chicago has to offer. It gathers over 7,000 times more light than the unaided human eye, allowing you to see celestial objects that are trillions of miles away. And we think that’s pretty cool!
With the Adler Planetarium currently closed until March 2022, the Doane Observatory is only open for select ’Scopes at the Adler events. Information about those events can be found here.
The following observing opportunities are currently unavailable while the Adler Planetarium is closed.
10:00 am–1:00 pm*
The Doane is open to the public periodically for safe, daytime telescope views of the Sun. We suggest inquiring at the Box Office when you arrive at the Adler to find out if the Observatory is open on the day of your visit.
Access to the Observatory is facilitated by Adler Planetarium telescope volunteers; as such, this schedule may change without prior notice.
Doane at Dusk
While the Observatory is open periodically during daytime hours, Doane at Dusk offers visitors a unique opportunity to see a variety of celestial objects, like Jupiter or Saturn, with nighttime telescope viewing. These events are offered throughout the year and are free to the public!
Often during evening events, the Doane Observatory is open for viewing or ticketed tours. These events include Adler After Dark, Family After Dark, and Members’ Night. Unsure if the Doane is open during the event you’re attending? Just ask an Adler staff member (in the grey and yellow shirts)!
Visiting the Doane
Where Can I Find the Doane Observatory?
Great question! The Doane is actually located outside of the Adler. You can find it to the east of our main building, right next to the shores of Lake Michigan. Just follow the sidewalk around the building. If the doors are open, you’re welcome to come on in and check out the sights!
Our Observatory is staffed by some of the most awesome, trained telescope volunteers this corner of the Milky Way. Each volunteer goes through technical training on how to operate a telescope and learns practical observing techniques. Plus, they’re equipped with a ton of cool facts and information about the Sun and other celestial objects.
Technical Details and History
We know some of you are wondering about the history and specs of our telescope, so here you go!
The telescope in the Adler Planetarium’s Doane Observatory was manufactured by PlaneWave Instruments, Inc. of Adrian, Michigan, and it was installed in 2020. This is the third telescope to be housed in the Doane Observatory in its 40+ year history. The first was a 16-inch telescope installed in 1977, and the second was a 20-inch telescope installed in 1987. The size refers to the diameter of the main mirror; mirror diameter is also known as aperture. Why’d we get telescopes with bigger apertures over the years? A bigger telescope means more light-gathering ability. More light-gathering ability means that dim objects appear brighter. Astronomy is all about seeing dim objects better.
The current telescope is a reflector. It uses a 24-inch wide curved mirror to gather light from distant objects. Reflector telescope design is often credited to Isaac Newton, and Newton created his reflector telescope in 1668. Newton was not the first person to think and write about using reflecting mirrors instead of transparent glass lenses in telescopes, but he was the first person to create a reflector telescope that actually worked. There are many different versions of reflector telescopes, and the differences are mainly due to the shapes of the various mirrors used in the design – spherical shapes, ellipse shapes, parabola shapes, and flat shapes. We still use Newton’s 350+ year old design in telescopes today. Why? Because it works!
Our telescope’s design is generally based on a telescope type called Cassegrain. Design notes about this type of telescope were published in the year 1672, and these notes have been attributed to a French Catholic priest named Laurent Cassegrain. In a Cassegrain-type telescope, light reflects off the concave main mirror, then off of a smaller convex secondary mirror, and then the light is directed through a hole in the main mirror to the eyepiece in the back. What’s the appeal for a Cassegrain-type design? It makes for a compact telescope.
The specific design that our current telescope is based on is called Dall-Kirkham. The concave 24-inch mirror is shaped as an ellipse, and the smaller convex secondary mirror is shaped as a part of a sphere. However, one problem with Dall-Kirkham telescopes is that objects at the edges of the view can appear misshapen and distorted. PlaneWave staff created a version of this design called a Corrected Dall-Kirkham, or CDK. There is a set of correcting lenses that is situated in the light path just in front of the eyepiece. What is the point of those lenses? This combination of mirrors and lenses creates images that are in focus and without distortions from one edge of the view to the other.
Our telescope is attached to an L-shaped mounting that continually moves so that it can precisely track celestial objects. The mount uses no mechanical gears to move the telescope. Instead, there are encoder reference points inside the mount, and precise pointing and tracking is obtained as the system compares the position of the telescope to these reference points. It is called a direct drive system. What advantages do we get out of using a direct drive mount system? The telescope moves very smoothly, very quickly, and almost noiselessly, and it has a very precise pointing ability.
But, why is our Observatory in downtown Chicago?
This means it’s much easier for you to get to us! Even in Chicago’s light polluted skies, we can spot planets, moons, stars, and more. We know our views could look better if the telescope was located far from city lights, but since our goal was to get your eyes up to our telescopes, putting the Observatory at the Adler made perfect sense in 1977 — and it still does 40+ years later.
Fun facts & info about our 24-inch telescope:
- In all, our telescope gathers about 7,000 times more light than your eye alone.
- Some of the internal pieces of our telescope were 3-D printed.
- Several parts of our telescope are made of carbon fiber.
- The mirrors of our telescope are made of fused silica and coated with a reflective layer of aluminum.
- The main part of the telescope is not a single solid tube. There are trusses & struts that connect pieces of the tube together, with openings in between. This keeps the overall weight of the telescope down and also helps with airflow through the telescope.
- Our telescope weighs 240 pounds.
- The L-shaped mount weighs 338 pounds.
- Even though our new 24-inch telescope is larger than our prior 20-inch telescope, the combination of carbon fiber pieces, open trusses, and 3-D printed pieces means that our new telescope and mount together weigh only about 1/3rd what our prior telescope and mount weighed.
- What’s the most distant object our telescope can see? That’s kind of a hard question to answer given the light pollution in Chicago, but if the sky conditions are really, really good, we might be able to catch 3C273, a quasar located in the direction of the constellation Virgo. 3C273 is about 2.4 billion light years away… meaning if you can spot this object, the light hitting your eyes left it 2.4 billion years ago.
Telescope: PlaneWave CDK24
Telescope focal length: 3974 mm
Telescope focal ratio: f/6.5
Mount: PlaneWave L-600 Direct Drive mount
Instrument & mount installed: January 2020
Balancing & tuning completed: August 2020
The Adler Planetarium is grateful to the Petrovich Family Foundation and Jeff Rothstein for their leadership and generous support of the Doane Observatory renovation.
Your all-access pass to our universe!