Solar Funnel Project

5″ Meade Newtonian reflector with solar funnel.

Doing star parties over the years I have witnessed long lines of party-goers queued up to take a peak through my telescope. I’ve found this to be the perfect time to talk to folks about what’s being looked at in the telescope. I like to throw out some fun facts and this always spawns more questions and curiosity in the gathered group. Talking to adults and kids about the night sky is one of the greatest aspects of doing star parties.

There is a limit to how many people can look through the scope at any given time, put simply it’s one at a time.  But when I saw this neat gadget called a “solar funnel” I immediately knew it would be great at eclipses to show participants the partial phases and better yet it could do this via projection so many people close by can view the eclipse at once.

After a quick study of what was involved, the materials needed, the construction of the device, etc. I decided to get to work on it. It seemed easy enough. I already had an eyepiece lying around that I could use. So all I really needed was the funnel, hose clamps, and the rear projection screen material. All total I spent less than $20 (minus the eyepiece) for these materials from the auto parts store, hardware store and online ordering the rear projection screen.

The solar funnel works as advertised. This will be a great tool to use during solar eclipses. While testing it out I saw birds, planes  and clouds all pass in front of the sun. I was able to see a very small sun spot as well. In my pictures there of course was not an eclipse in progress so the sun appears round.  Alas, I can’t post any eclipse pictures with it just yet but at this writing we are only 3 months almost to the day away from the total solar eclipse on August 21, 2017.

To give the sun the orange color in these pictures I threaded on a #23A orange filter just for kicks. Otherwise you can use a yellow filter or no (eyepiece) filter at all for a white sun.

The solar funnel is best utilized with a small refractor telescope. You might be saying “then why are you using a reflector telescope?” As long as you stop down the optical tube to one or two inches by using an aperture mask (see first picture on this post) you can use a Newtonian reflector. Not stopping down the telescope can be dangerous and will result in permanent damage to your reflecting telescope.

This device is not recommended for catadioptric telescopes or scopes that incorporate both lens and mirrors. Also, be sure and remove or cap off your finder scope before observing the sun. This is also a good time to give the obligatory warning about never looking at the sun with your naked-eye or especially with a telescope if you are not absolutely sure about your equipment and filters. Seek professional assistance before you attempt to observe the sun if you are unsure. They’re your eyes. You only get two (in most cases) so use them wisely.

The solar funnel instructions can be found here. This was an easy and fun project that I’m sure will be a crowd-pleaser at eclipses.

Update – Here are some pictures of the solar funnel in action during the total solar eclipse of 8-21-2017


Happy eclipse chasing!