Family Science: Pinholes and Safe Solar Viewing

By Amy Cowen on May 21, 2012 12:13 PM

Creating a pinhole projector for the eclipse encourages hands-on family science—and offers a lesson in perseverance. Family science doesn't always turn out exactly as planned, but everyone learns something along the way. Tubes, tape, and a pinhole lead to unexpected reflections of the eclipse for this family.

Positioning a pinhole projection tube takes some practice, but this kind of hands-on family science activity encourages active thinking—and troubleshooting!

Making Connections
You can springboard your experience with pinhole systems into a more extensive exploration of pinhole cameras! These Science Buddies Project Ideas can help get you started:

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Form and Function: A LEGO Camera

I am not a scientist. I am a writer who works for Science Buddies, and so I approached yesterday's eclipse not as one of my scientist colleagues might, but as a mom who tries to make science and DIY a part of everyday life for her two kids. Sometimes what we try works, but not always.

After all the research I did last week on the eclipse and on possible ways to safely view the eclipse, I wasn't sure we should even bother trying to view the eclipse. Part of me worried that my youngest would be unable to resist the temptation to look at the sun despite all my warnings of the dangers. Part of me worried that seeing a projection of the eclipse about the size of a quarter and in black and white would be anticlimactic, especially compared to the stunning full-color photos of eclipses online. But part of me, the part that is more and more attuned to the importance of taking advantage of hands-on family science opportunities like this one, felt like we shouldn't miss the chance to try our own pinhole viewer, especially since the Venus Transit in early June will also require a pinhole solution.

The Planning Stage

Before the sun rose on Sunday morning, I spent time scouring online directions, trying to figure out the most sure-fire approach—and the one most likely to work with what we had on hand. That the materials for a pinhole viewer can be scrounged up in your average basement and for little or no budget was a plus. We decided to try a tube-style pinhole projector, rather than a shoe box viewer, mostly because the Exploratorium directions I reviewed recommend a tube at least 6 feet long and offer a correlation between the tube length and the projection as approximately 1 to 1/100th—the image projected with be 1/100th of the length of the tube.

"The length of the box is important. The longer the box, the bigger the pinhole image. To find the size of the image, multiply the length of the box by the number 0.0093. If your box is 5 feet (60 inches) long, your solar image will be 60 x 0.0093 = 0.56 inches in diameter."

With this "six foot" recommendation in mind, I worried that a "shoebox," probably measuring in at about a foot and a half, would yield too small of an image to generate any real wow factor. While the directions made use of long triangular boxes, other sites suggest you can use wrapping paper tubes or similar "lengths" of cardboard tubing. Looking around the house, I spotted a few tubes in varying states of decline from having been used as a sword or bat. Game to join in the project, one of my sons turned up two empty toilet paper holders. We gathered tape, scissors, a few index cards, a sheet of cardstock, a pin, and headed to the backyard. (We couldn't find the aluminum foil for the pinhole, so we decided to test with paper and then buy foil before the official observation.)

Trial Run

Knowing that sometimes even the simplest of projects don't pan out as I expect—or as easily as directions indicate—my thought was to assemble our tube and try it out in full sun to make sure we could project an image onto paper. That way, I reasoned, we would be ready later in the day for the eclipse. Once outside, we got started. Knowing that our small backyard is a bit of a wind tunnel as it flows down the hillside from a high point in San Francisco, we taped a piece of white cardstock to a large wooden board that we use for mounting in-progress watercolor paintings. This let us put the surface on which we wanted to project our image on the ground without it blowing away either during our testing—or during what turned out to be a long session of taping!

The Exploratorium directions involve creating a pinhole covering on one end of the tube and then cutting a viewing opening into the side of the tube near the bottom, similar to the way shoe box viewer designs are constructed. The image is then projected onto the bottom wall inside the tube. With the small diameter of the wrapping paper tubes, it didn't seem likely that cutting a viewer into the tube would work or offer much viewing space. Given that you can create a basic projection with your hands or a piece of paper, we thought we might be able to project through the length of the tube and onto paper, without a side-viewing opening—and cast the image onto paper instead of into the bottom of the tube.

Exploring the Variables

At the outset, we wanted to prove to ourselves that this process "could" work before we worried about creating a bigger and better pinhole apparatus. So before we began our attempts to connect various tubes, we made a paper circle to cover the end of the sturdiest tube, taped it on, and carefully poked a pinhole. We then took turns trying to project an image through the pinhole and onto the paper. Positioning the tube precisely so that only its opening was in shadow and the small circle of light appeared on the paper can be more difficult than it sounds, but my fifth grader immediately understood how to move the tube to get it in the right place. (Throughout our testing, he had better luck with this process than i did!)

Initially dismayed by how small the projected circle was, we talked about different lengths of tubing and about different diameters of pinholes. Although everything we had read indicated we needed a very careful and small pinhole, we wondered if a larger pinhole might yield a larger projected image. We tried holes of varying sizes. We tried just a sheet of paper, knowing that one of the simplest ways to project is with a single sheet of paper and a single pinhole held above another sheet of paper. We held up a toilet paper roll and immediately cast a large circle on the paper. "But Mama, that's just pure light," insisted the oldest. Returning to our sample single tube, which was casting the expected circle, we started connecting two long tubes, adding torn index cards to help shim the slight differential in diameters, taping extra index card pieces around the seams to help block light, and adding lots and lots of tape.

Unfortunately, when you hold a six foot or longer wrapping paper tube in the air, there's a good bit of bend. That problem magnifies when one of the tubes has been played with and suffered during one battle or another. We spent a good bit of time troubleshooting stray bits of light, peering through one end or the other to ensure we could see clearly through the tube, finding a stick to knock out spider webs we discovered were partially blocking our view through the tube, and taping and retaping to try and stabilize the tube so that it wouldn't bow or collapse when we held it up high. (Note: we did not look through the tube at the sun.)

Show Time

We planned our day with the eclipse in mind, and when the optimum viewing time rolled around, we gathered our things and headed outside. The difference in trying to find the projection point with the sun so low in the sky was immediate. We had to stand much farther back from the paper than we had mid-day to position the shadow on the paper, and we had much more trouble finding the spot. Even when it seemed we had the tube's shadow positioned properly, we were not seeing the pinpoint. We were seeing the eclipse, however. We kept seeing the crescent shape that we knew meant the moon was in place, obscuring most of the sun, but we were seeing it as a result of our hands. The tiny opening of my hands around the tube was casting the eclipse image to the paper. The eclipse was in progress, but we couldn't find it with the projector.

Thinking that maybe our angle in relation to the sun, keeping in mind we are downhill with a fence rising behind us, might be causing a problem, we headed to the street and then to the top of the hill, hoping that at the clearing we would find an optimal spot. As we walked up the hill, bracing our pinhole tube projector against typical San Francisco winds, I continued my cautions about looking at the sun, more concerned than ever that the temptation would be too great once we reached the clearing and were facing the sun directly as it sat out over the ocean, which is visible from the hilltop.

We reached the clearing, turned out backs to the sun, and positioned our wooden board, which we had to move into the street to give ourselves enough room to cast the shadow. We saw the crescent over and over again, but we never did successfully see the pinhole projection. While we struggled to make it work, someone pulled up across the street in a car with solar glasses on and sat back to enjoy the solar show. Giving up on the long tube, we separated it and tried to use only the smaller length, hoping the single sturdy tube would give us an image. As we continued to struggle, another group of young adults showed up, hopped out of their car with a small shoebox projector, and immediately found pinpoint success. "There it is!" After more failed attempts to find our own image, I asked if we could take a look, and, indeed, we both saw the smaller-than-a-dime-sized crescent of the eclipse, clearly cast onto the far end of the shoebox.

Best-laid Plans

Disappointed that our hard work, testing, and planning hadn't paid off, we headed back down the hill. As we walked up the sidewalk to the house, we noticed that a neighbor's bush was casting a shadow onto the side of our house, and in every light spot, we could see a crescent. Hundreds of tiny crescents. Once upstairs again, we looked out the back window and saw a similar effect on a fence down the hill where a tree's shadow was showing the eclipse.

Our pinhole projector didn't work. As a parent, it was disheartening to have our science activity fail, and I spent a good bit of time apologizing that it hadn't worked. I know we each learned something, and that our afternoon of testing and questioning was important, but we didn't succeed, and that's frustrating. I really wanted the experience to "work." It didn't. Next time, we take what happened this time, change our approach, and try again. I haven't given up, but my son is clear that for the Venus Transit, he wants to use a shoebox.

Epilogue

Home again, defeated by what should have been a simple astronomy project—one perfectly suited for my DIY-minded household—I logged into Facebook. The first image I saw was from a friend who is also an elementary school teacher. Her family had created what, compared to our wrapping paper tube, seemed like a most enormous pinhole projector. Seeing it perched in the arms of a tree, I could only shake my head and laugh. Even with science, it is critical to keep everything in perspective.

When he came home from school the next day, my fifth grader reported that when they talked about their weekends, more than half the class had tried to observe the eclipse. According to their class discussion, we were not alone. Only a few of them had success with the kinds of viewers they tried to build and use. That we were at least one of the ones that had tried... matters.

When our lead scientist reviewed my experience and the trials and tribulations of our failed pinhole projector, her advice was immediate: try the shoebox version next time—and get some aluminum foil.

Venus Transit... here we come!