Abstract

Encouraging learners of all ages to experience solar eclipses safely is one of NASA’s main priorities and goals during these beautiful and awe-inspiring celestial events. Besides ISO certified solar viewing glasses and other direct viewing methods, a pinhole projector is a safe, fun, and educational tool for observers of all ages to use. The NASA Heliophysics Education Activation Team (NASA HEAT) has developed and made available 2D and 3D pinhole projector files in the shape of the continental U.S. map and a companion activity with a math extension.

1. Introduction

On Monday, April 8, 2024, a total solar eclipse will cross North America1, passing over Mexico, the United States, and Canada (Figure 1). The entire continental United States will experience a partial eclipse. Those on the path of totality from Texas to Maine will experience a total solar eclipse. A total solar eclipse happens when the Moon passes between the Sun and Earth, completely blocking the face of the Sun. The sky will darken as if it were dawn or dusk.

If you are in the path of totality during the solar eclipse in April 2024, during the totality phase, where the Moon fully blocks the Sun, it is safe to take off your solar viewing glasses for the brief phase of totality. The totality phase can reveal different solar features that are otherwise not visible, such as the chromosphere and the corona which are different and fainter regions of the solar atmosphere. The only safe way to look directly at the uneclipsed or partially eclipsed Sun is with specialized eye protection, such as solar viewing glasses (“eclipse glasses''), a solar viewer, or through a telescope with a solar filter. These special-purpose solar filters must comply with the transmittance requirements of the ISO 12312-2 international standard. Many communities and individuals search for solar viewing glasses (Figure 2) to observe this celestial wonder, but find they are unavailable immediately before an eclipse.

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While direct viewing methods are popular, the solar eclipse can also be viewed indirectly. Pinhole projection allowed early scientists to view the shapes of illuminated objects, like the Sun, by shining the light from the object through a very small hole (aperture), which acts like a simple lens by projecting an image of the object onto the ground, wall, or other flat surface. A pinhole projector, as simple as a piece of paper or box with a hole in it or a colander, can be used to observe a partial or annular solar eclipse. An engaging indirect viewing tool one can make is a “continental USA map pinhole projector” that has a round hole in the middle and a star for the US capital. This tool is available in 2D paper cut and 3D printed/laser cut versions (Figure 3).  

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2. Approach

In 2016 we prototyped a 3D printed handheld board with multiple holes of different sizes (Figure 4). We took this board to Micronesia to demonstrate and optimize the tool during the total solar eclipse on March 8, 2016 and experimented with hole size and pinhole projector distance from the ground. We were looking for the aperture that would feel comfortable for an average height user to hold the tool above the ground. With a testing range of 0.6 mm to 6 mm projecting hole sizes – which is a trade-off between image sharpness and brightness – we determined the best projecting hole size to be 5 mm. This was determined for a board to ground distance of around 1 meter, which is a comfortable height for most people.

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When we returned from Micronesia, the idea came about that the shape of the board should be somehow incorporated into the overall design so that a user would see the outline of the shadow of the shape (Figure 5). Eventually, we created a connection between the product and the user by having a nation shaped pinhole projector that would be available as a 3D printed and a 2D paper cut version. The original nation-shaped file would include the path of totality, partial eclipse percentage lines, eclipse website URL, the 2017 eclipse identifier, and most importantly the pinholes, a 5 mm circle in the middle and a 5 mm star locating the US capital (Cline, et al., 2020). 

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To further deepen the connection between users and the products, we designed and developed 2D and 3D models for each of the 50 states, several territories, and special locales including the Navajo Nation, the Cherokee Nation, Prince William Sound, the U.S. Virgin Islands, and Puerto Rico. Each of those models included the same features as the original nation shaped pinhole projector; outlines, partial paths, and state capitals designated by an additional star shaped projection hole.

Team members at NASA’s Goddard Space Flight Center then experimented and developed 3D models for multicolor prints that added visibility and aesthetics. They also left room for accessibility improvements, cross cutting technologies, and exciting people to get involved in 3D printing. Many libraries, schools, and community maker spaces have 3D printers, but often educators and learners do not know what to do with the technology. A 3D printed map in the shape of a familiar state, territory, or country that doubles as a pinhole projector can add significant joy and engagement to the STEM learning experience. It also allows for hands-on learning experiences that integrate emerging technologies in STEM environments.

3. Results

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Users are able to download both the PDF and STL files2, each scalable for 2D and 3D use, respectively - depending on the levels of sophistication in their environment (low to high tech offerings). They can print in layers with state colors or customize it like the University of North Texas did through the creation of a real postcard (Christensen & Knezek, 2023). Users can take the pinhole projector, in the shape of a map of the 48 contiguous United States, outdoors in the Sun. With their back toward the Sun, they hold the map approximately one meter (about three feet) above the ground. This allows the sunlight to shine through the holes in the map onto the ground, projecting an image of the Sun. (Figure 9). 

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That USA map 3D printed projector was introduced at conferences to educators and librarians leading up to the 2017, 2023, and 2024 solar eclipses. Though the team did not have a specific count of the number of downloads, many librarians and technology educators shared anecdotal accounts about the popularity of the tool. This even included a 3D printing YouTube channel that utilized the design and presented it in a video (3 D Printing Nerd, 2017). At the same time, designers and users learned that some state borders were more difficult to print than others. There were also simple physics questions: would the shape of the pinhole matter (such as, the added benefit of the additional star shaped hole)? Would the size of the hole matter? What about different distances from the ground?

Built on the successes of 2016 and 2017, the NASA Heliophysics Education Activation Team (NASA HEAT) iterated upon the 2D and 3D printable files for the 2023 annular and 2024 total eclipses across America with an instructional activity and math extension. The math extension focuses on using a simple ratio to determine the relationship between the Sun’s height, the Sun’s distance from Earth, the projection distance, and projection image height (Figure 10). To create their own projector, users have a choice of low to high end technology opportunities ranging from laser cutting, 3D printing, plain printer paper, to die cutting machines.   

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For the 2023 annular and 2024 total solar eclipses, observers have more choices of pinhole projectors. For example, NASA’s Marshall Space Flight Center posted a 3D printable map. The Night Sky Network, the GLOBE Observer, and the PUNCH mission all provided cardboard disks with pinholes. 

NASA HEAT is happy to provide a USA map pinhole projector as an educational tool and an authentic experience for STEAM learners. The activity3 is aligned with the Next Generation Science Standard MS.ESS1-1 - “Develop and use a model of the Earth-Sun-Moon system” to describe the cyclic patterns of lunar phases, eclipses of the Sun and Moon, and seasons. There is the science of pinhole projection, the technology of creating or modifying one, an engineering exercise (behind the scene) to design and scale the map, an art aspect with coloring, and a math problem to scientifically determine the Sun’s diameter or distance from the Earth. It’s also possible to add a lesson on local or state geography. The hole doesn't need to be round: a circle, a star, or a square shaped hole - even a grid formed with two hands - will project the same images of the Sun. It’s not the shape of the hole but the size of the aperture. Even if you are on the path of totality on April 8, you may safely observe the Sun with this USA map pinhole projector during the partial phases. It’s a great tool for observation of a physical process and basic optics principles. 

4. Future Work

A team member showcased the pinhole projector in an accessibility workshop and continues to iterate and test the file with different groups. Participants made recommendations to the design, including raised features, high contrast colors, and percentage of eclipse in braille for low vision users. These features will be implemented and tested with other accessibility groups moving forward.

As the Sun approaches solar maximum in the 11-year solar cycle, many activities may happen daily on the surface and in the atmosphere of the Sun. Some of these features, like sunspots, may be observed with pinhole projection. There are natural ways to implement pinhole projection: anything that has a small hole surrounded by a sufficient amount of light blocking material. One of the many great aspects of pinhole projection is the shared group viewing experience of the Sun. Ultimately, it is possible to build a classroom sized pinhole projection, potentially increasing the number of visible solar features. This shared learning environment allows users to view and understand different scientific concepts in a group setting.

5. Conclusion

Pinhole projection has proven to be a great way to engage learners of all ages with science and instrumentation. It has the added benefit of aligning with one of NASA’s main priorities: safety. This indirect viewing method is a great way to engage learners not only in group observations and activities, but with the celestial event itself and to extend that knowledge through STEM exploration. 

Acknowledgment

This activity is supported by the NASA Heliophysics Education Activation Team (NASA HEAT), part of NASA's Science Activation portfolio. The lead authors are grateful to the support of the NASA HEAT Principal Investigator, Dr. Michael S. Kirk of NASA’s Goddard Space Flight Center.