Pinhole Viewer: Trying Again for the Transit

By Amy Cowen on June 4, 2012 4:40 PM

The Venus Transit offers a wonderful opportunity for family summer science and an easy DIY science activity—making a pinhole viewer. From parallax to exoplanets, tomorrow's transit raises plenty of talking points for students and their families, but a safe viewing strategy is a must.

During the Venus Transit, Venus will appear as a dark spot crossing the face of the Sun. Safe viewing is a must, but families can witness this event, which won't happen again until 2117, using a simple pinhole viewer. It's a great opportunity for summer science! Image: Jan Herold, Wikipedia

This afternoon, our family science activity will involve cardboard and aluminum foil as we make a pinhole viewer in hopes of catching tomorrow's Venus Transit. Given the sad-but-true tale of our pinhole tube projector attempt last month for the eclipse, we will be making and trying a shoebox pinhole viewer this time—and hoping for much better results. Having briefly viewed the eclipse through a shoebox viewer another group brought to the top of the hill where we were struggling to catch an image through our makeshift tube projector, we have a good sense of how small our viewing of the Venus Transit will be—and with a transit, unlike an eclipse, Venus will appear only as a small dot as it crosses the surface of the Sun. Still, we're hoping for clear skies and a clear view.

Pinhole Planning

In preparation for the coming transit, I spent time talking with Terik Daly, Staff Scientist at Science Buddies and a doctoral student studying planetary science at Brown University. In part, I wanted to know how off-base we had been with our viewer attempt last month.

After reading through my account of our viewer, Daly confirms, much to my relief, that in theory what we tried should have worked. Something went wrong, but the concept was sound—and we were able to cast the Sun during the afternoon, just not later during the actual eclipse. (I still think the heavy winds at the top of the hill didn't help us—or our taped-together cardboard tubes, which seemed even more flimsy when held up into the wind.) Daly did note that aluminum foil, because it is opaque and highly reflective, might have increased our chances of success.

What's the Big Deal?

The Venus Transit is a 243-year cycle, arriving in pairs, eight years apart, separated by first 121.5 years and then by 105.5 years. The last Venus Transit was on June 8, 2004, making tomorrow's transit the second in this transit cycle. The next Venus Transit won't be until 2117. Those numbers alone are important, but as noted in recent Scientific American coverage of the coming transit, this year's transit will be one of a small handful of transits that have been recorded: "Only six transits have been observed in history: in 1639; 1761 and 1769; 1874 and 1882; and 2004."

Beyond the fact that you may only get one or two chances to see a Venus Transit in your lifetime, the coming transit is a big deal for astronomers. Historically, transits helped astronomers gauge the size of our solar system. "Until the 20th century it was the only way to determine the distance from Earth to the Sun," reports Jay Pasachoff. As Summer Ash explains in a post on Scientific American's Budding Scientist blog, astronomers used the principles of parallax to determine the distance of the Sun from the earth. Using measurements from two viewers at different locations, the distance from the sun can be triangulated. With that measurement in hand, the "distances to all the other planets known at the time could be derived." Based on calculations made during the Venus Transit of 1882, Ash notes, astronomers concluded that the Sun is 93 million miles away.

A Model for Exoplanet Research

According to Daly, transits continue to offer astronomers useful information, particularly because transits can reveal exoplanets. "Transiting is one of the major ways that astronomers detect extrasolar planets," says Daly. "NASA's Kepler mission, for example, has identified over 2300 exoplanet candidates (with 61 confirmed exoplanets) using transit techniques."

The Venus Transit, he explains, offers the general viewer a better understanding of how transits work, which in turn helps explain how astronomers are able to use transits to detect exoplanets near other stars. Those watching the Venus Transit will see a decrease in light from the Sun as Venus crosses in front of it. In the same way, astronomers observe and track the light from other stars. "Decreases in the amount of light detected from a star indicate that something is blocking that light, and if those decreases are periodic, it suggests the object doing the blocking is orbiting the star—a planet," says Daly. "Of course, detecting extrasolar planets is more complicated than that," he adds. But "this transit is a fantastic opportunity to conceptually understand 'transit timing,' an important method of exoplanet detection, the method used by NASA's Kepler spacecraft."

Venus Transit as a Benchmark

In addition to helping demystify the search for—and discovery of—exoplanets, Daly notes that the transit offers additional information about Venus, including more data regarding the composition of Venus' atmosphere. "While we have other ways to study Venus' atmosphere, transits are one of the very few sources of information about the composition of exoplanet atmospheres," explains Daly. "The Venus Transit is a chance for scientists to test their methods for using the light from exoplanet transits to understand the atmosphere of the transiting planet." In other words, studying Venus' atmosphere via the Venus Transit—and comparing that information to other known data—helps astronomers corroborate the approach of drawing conclusions about an exoplanet's atmosphere based on its transit.

Making Connections

Students and families who will be observing the Venus Transit can learn more about how the transit helped astronomers understand our solar system by learning more about how parallax works. The "A Puzzling Parallax" project is an introductory project that can help families better understand the relationship between distance and viewing perspective. For an immediate example, close one eye and hold a pencil out in front of you, lining it up with an option in the distance (a light switch, a tree, etc.). Now switch eyes. This distant object is no longer lined up with the pencil; it will appear to have shifted . This shift based on the difference in viewing perspective is central to parallax. Using hula hoops and a ruler, you and your family can explore further! For a more advanced study of parallax, see "Similar Triangles: Using Parallax to Measure Distance." (The project is more difficult, but the introductory material may be perfect for better understanding the concept of parallax and talking about it with your students.)

In addition to studying parallax, building a pinhole viewer gives you and your family a chance to build a simple scientific apparatus. The following Projects Ideas and resources can springboard some fun exploration of pinhole cameras:

Sources Referenced Above for Additional Reading: