The Sun Funnel is a device for telescopes that allows a group of people to observe a magnified image of the sun safely. Make your own Sun Funnel, which attaches to an existing telescope, to share a solar spectacle with a larger audience.
Image: Rick Fienberg
I like to use a Sun Funnel when observing the sun with a large crowd. Only one visitor can look through the eyepiece of a solar-filtered telescope at a time. As a line of people forms, I set up a separate dedicated telescope with Sun Funnel so those waiting their turn can participate in observing the sun a unique way. I do not run a clock drive, for the rig is suitable for the public to slew the telescope by hand as the sun moves off the screen. If you are doing public outreach with a telescope by day, consider a Sun Funnel to improve your visitor's experience.
Start here. This document has all the instructions, images, and caveats for making a Sun Funnel and observing the sun. Version 3.4 updated 2020 by Rick Fienberg.
Prepare for the solar eclipse on Monday, August 21, 2017. While all of North America will see a partial eclipse, people within a narrow swath from Oregon to South Carolina will see a total solar eclipse. Learn about eye safety when observing the sun.
The Sun Funnel is suitable for observing solar eclipses, sunspots (umbra and penumbra), and transits (Mercury, Venus, and even ISS). Read all warnings to prevent personal injury or telescope damage when observing the sun.
Share the URL for how-to instructions with this handout summarizing the Sun Funnel. Encourage others doing public outreach to set up a dedicated telescope with a Sun Funnel for visitors to track the eclipse live as a group.
3D Printer Version
Added 2017 Aug. 6:
Try these .stl files
3D Sun Funnel made by Adler Planetarium; image courtesy of Steve Burkland.
Short video introduces the Sun Funnel and demonstrates how to use it on a telescope to observe the sun safely. Of course, on the day we filmed there were no sunspots.
The text for the 3D Printer Video summarizes how to make and use the device. Download video's one-page script.
Make a 3D Printer Sun Funnel
With a 3D printer, a 5-inch tube that is ten inches long, and some projection screen, you can make a Sun Funnel. See the video below for overview, but also read the original instructions and requisite warnings.
The 3D printer files in .stl format are free to download:
Updated .stl files are coming around the first week of November.
Note: On the outside of these parts are holders for wooden dowels for making a truss, or you can use the 5-inch diameter tube. The open truss, though weighing less, lacks the security of the fully enclosed tube. You can wrap the truss to enclose the cone of light, and add promotional text on the wrap itself.
The Sun Funnel was first developed by Gene Zajac and Chuck Bueter as a modification of Bruce Hegerberg's "Sun Gun." After Gene and Chuck led workshops for the Great Lakes Planetarium Association, the Sun Funnel saw widespread use during the 2004 Transit of Venus.
Rick Fienberg printed and illustrated detailed instructions, complete with mathematical underpinnings, for an Astronomical Society of the Pacific workshop with Chuck Bueter and Lou Mayo in advance of the 2012 Transit of Venus. The Sun Funnel's popularity spread, as users around the globe made Sun Funnels to witness transits of Mercury, Venus, and the International Space Station.
Anticipating the 2017 solar eclipse, students from the Career Academy South Bend designed the 3D printer version of the Sun Funnel.
In July 2017, Adler Planetarium modified the design, 3D printed several samples, and shared their .stl files. Please access the Adler .stl files at https://www.dropbox.com/sh/fxvdekmf6y3h4it/AACOi-ZNcX0ZOEhz4oG4V-5Ya?dl=0.
Here are images showing just a few of the parties who have helped usher the Sun Funnel along. Thanks go to all who contributed to the process.
Images last updated after pre-eclipse conference in Carbondale.
3D-printed Sun Funnels at Adler Planetarium. Image courtesy of Mike Smail.
Dave Prosper captures the moon with a Sun Funnel in a 5-inch telescope. Image courtesy of Dave Prosper.
Image courtesy of Steve Accuosti.
Screen Shot 2016-06-07 at 1.03.37 AM.png
sun funnel lens holder
original and 3D printer versions
Image of Sun Funnel prototype at GLPA conference courtesy of Mike Smail.
Nightwise.org : Sun Funnel.png
Not-So-Fine Print: Eye Safety
Viewing the sun without proper equipment and/or techniques can result in serious eye injury or blindness. The solar observing descriptions, images, and comments listed within this website are not an endorsement of any particular technique or product. Observers are responsible for their own eye safety. This website accepts no responsibility for the conduct of others in viewing the sun. If you use commercial eclipse shades in 2017, be sure they are ISO-approved.
For advise on observing the sun, see Dr. Ralph Chou's video about Viewing the Transit & Eye Safety. A definitive document on eye safety from NASA and its education partners is expected in late 2016.
Making a Pitch
At an Elevator Pitch Competition on February 25, 2015, I sought an entrepreneur to develop the Sun Funnel for his/her commercial gain. Thirty seconds. Go!
Solar Projection Tool
Rick Fienberg demonstrates the ultimate solar projection tool that you always carry with you--crossed fingers.
Space Station Transit
The International Space Station is visible zipping across the bottom half of the sun, right to left, on an oversized Sun Funnel as ISS transits the sun.
2017 June 30
Jerel Williams writes:
“Build a Sun Funnel for Group Viewing of the Great American Solar Eclipse of August 21, 2017”
S=fA x (180°/π) should read S=fA x (π/180°) or S=fA / (180°/π)
2017 July 23
Steve Burkland of Adler Planetarium writes :
“…We had to make adjustments to the STLs because they were two small to work with. These versions are sized for a 1.25" eyepiece to be threaded into it. You can find the STLs at this dropbox: https://www.dropbox.com/sh/fxvdekmf6y3h4it/AACOi-ZNcX0ZOEhz4oG4V-5Ya?dl=0.”
Note: Other people have made improvements and modifications to the original Sun Funnel design. I just haven't had time to acknowledge them properly. I thank them for their contributions to the effort. -Chuck
How to make a Sun projector, by Neil Zimmerman and Michael Hepler
Tom Mangeldorf writes: 2017 July 20
I made one for my 60mm 'scope. I noticed that the lid from a Quaker Oats oatmeal package is just a little bigger than the top end of the funnel, so I glued it on thusly:
The fact that the edges of the lid are slightly raised over the center portion keeps the center portion shadow, which also helps.
I will be catching a 50% eclipsed Sun from the lawn at the Anchorage Museum in Alaska. The sun funnel will be great for people to be able to use their cell phones to take pictures of the eclipse. Plus, they can take pictures of each other standing next to the projected image for their Facebook updates!
From time to time, I set up my 5" refractor with full aperture solar filter at the museum show people sunspots, faculae, limb darkening, etc. This picture was taken on International Astronomy Day in April 2017. I will have it there for the eclipse too. Here's hoping for clear skies!!!!
..The other thing is that the center of the oatmeal container lid had a little "feature" on it similar to the little thing on the side of the funnel that had to be sanded off. ...it's small, and won't be an issue for showing the changing "shape" of the eclipsed Sun as the eclipse progresses.