Doane Observatory

Side view of the Doane Observatory on a summer's day.

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!

Observing Opportunities

We are looking at ways to open the Observatory on select Wednesday nights during Adler at Night (also known as Illinois Resident Discount Days/free days).  Weather makes the schedule a bit unpredictable so check in at the box office on the evening of your visit to inquire about the availability of the Observatory.

Visiting the Doane

Image Caption: The Adler Planetarium Doane Observatory July 2021

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!

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.

Our Team

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

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.

Fun Facts About Our 24-inch Telescope

Adler Planetarium 24" reflecting telescope in the Doane Observatory after installation in 2020.
Image Caption: Adler Planetarium 24″ reflecting telescope in the Doane Observatory after installation in 2020.
  • 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.
  • Technical Information About The Telescope

Thanks To Our Sponsors

The renovations to the Doane Observatory and the Observation Park completed in 2021 have been supported by passionate donors including tremendous support from: Founding Donor, The Petrovich Family. Lead support was provided through an Anonymous donor and the Public Museum Capital Grants Program of the Illinois Department of Natural Resources, Illinois State Museum.

Additional generous donations were provided by: the A. Montgomery Ward Foundation, John A. Hutchings, Richard W. Oloffson and Bank of America, N.A., Trustee, Thomas J. Anderson and Family, the Brinson Foundation, the Dr. Scholl Foundation, Mr. and Mrs. John W. Estey, Mr. Joseph T. Lower, Mr. and Mrs. William J. Lutz , The MacLean Family, Mr. and Mrs. Jeffrey S. Rothstein, the Searle Family, and Sidley Austin.

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