The total solar eclipse of April, 8 2024 was viewed by millions of people on the North American continent,1 including me. I teach at Bradley University in Peoria, Illinois, only about three hours northwest of the path of totality. Having an interest in astronomy for most of my life, and having seen totality during the 2017 North American eclipse,2 my family and I all took time off see this eclipse. We ultimately viewed the eclipse in a park in Casey, Illinois, home of the world's largest rocking chair, mailbox, golf tee, and other items.3 I want to share a few thoughts about my eclipse experience from the perspective of chemistry and other STEM fields. This post does not contain any actual pictures of the eclipse itself. Readers can find many pictures of the eclipse online.4
On the way to and from the eclipse we passed near oil fields in eastern Illinois where oil was being extracted from the ground with pumpjacks, Figure 1. We noted the smell the hydrogen sulfide in the air in that area, which reminded me of an oil field that I once smelled near Odessa, Texas. Hydrogen sulfide can be a serious hazard in the petroleum industry. In addition to its awful smell, it is toxic, flammable, and corrosive.5 It also reminded me that sulfur compounds are a problem associated with many fossil fuels, that, when burned, convert to sulfur oxides which contribute to acidity in rainwater.6 I noted this to my chemistry class the next time we met after the eclipse, since we had previously discussed acid rain.7
Figure 1. Oil pumpjack among purple flowers in eastern Illinois field.
We used a number of methods to observe the eclipse itself. We had access to a variety of Vernier probe systems through Bradley University. We set up a UVB sensor pointing in the general direction of maximum eclipse, as well as a thermometer, to track UVB intensity and temperature as a function of time. We deployed one pair of probes near Peoria where the eclipse reached greater than 90 percent coverage but not totality.1 The graphs in Figure 2 show the data acquired at that location. On a typical sunny day, one would expect the sunlight to increase from morning until the middle of the day and then decrease until evening, and the temperature would be expected to follow a similar track. Both sets of data clearly show temporary decreases in UVB intensity and temperature during the time of the eclipse. We deployed a second set of Vernier probes in Casey, IL, situated in the path of totality. The graphs in Figure 3 show the data acquired at that location. Both sets of data clearly show decreases in UVB intensity and temperature during the eclipse, but the minimum in the graph of the temperature data occurs later than the minimum in the graph of the UVB data. It seems to have taken the air temperature some time to respond to the changes in light intensity.
Figure 2. UVB intensity and temperature as a function of time measured near Peoria, IL, on the day of the eclipse.
Figure 3. UVB intensity and temperature as a function of time measured in Casey, IL, on the day of the eclipse.
Another way to observe the change in light intensity during the eclipse was to monitor the energy production of a solar array over time. The graphs in Figure 4 show the data acquired at a solar array at a colleague’s house in Peoria, again with a prominent data gap corresponding to the eclipse. In a more chemical approach to measuring light intensity, a student observing totality during the eclipse wore beads that contained dyes that turned reversibly from colorless to colorful when they absorbed UV light, breaking chemical bonds and changing the geometry of the dye molecules. Students observed that the UV light sensitive beads reverted from colorful toward colorless in the dim light of the eclipse.8
Figure 4. Energy production as a function of time measured at a Peoria, IL, solar array on the day of the eclipse.
To observe the eclipse more directly with our own eyes, eclipse glasses were used. A recent “What’s That Stuff?” segment in Chemical & Engineering News noted that the lenses of eclipse glasses are comprised of polymer films that contains carbon black to absorb light.9 Some films are also metallized with aluminum metal to reflect some of the sunlight.9 Since the polymer films in the glasses can absorb light so well, samples of glasses were exposed to lasers to see if they could be thermally damaged by the light. CAUTION: Use of lasers carries the risk of their intense light doing damage to objects. This not only includes light emitted directly from the laser, but also reflected light. Exercise extreme caution when working with lasers to avoid eye damage! Eclipse glasses with any damage to them are useless for viewing eclipses, so they must not be recycled after sustaining laser damage.
In many cases, the lasers thermally damaged the plastic and eventually melted a hole through the film. Visually, this would appear as no light initially penetrating the polymer, followed by some light penetrating to produce a distorted, often shifting, image onto a surface. Eventually the laser completely penetrates the film to produce a small bright laser dot on a surface. For one of the samples, the distorted laser images appeared as a series of concentric rings, such as those shown in Figure 5. This was similar to the effect produced by lasers shined through other polymer films and solvents that contained light-absorbing substances, including carbon-based soot.10 An explanation for this effect is that the medium absorbed the laser light, which heated the medium and changed its refractive index. The laser light waves passing through this thermally altered medium exhibited constructive and destructive interference to produce concentric ring patterns.
Figure 5. Diffraction patterns formed on wall by shining intense lasers through eclipse glasses lenses.
For me, the most amazing thing scientifically had to have been seeing the solar prominences during totality, appearing to my eyes as a little dot or two at the edge of the moon shadow (especially at the “bottom” of the circle from my perspective). I especially began to appreciate what I had seen when I read more about them in the days after the event.11 I learned that their reddish glow was largely due to the excited hydrogen that they contain. The hydrogen-alpha electron energy transition used extensively in astronomy produces red light with a wavelength of about 656 nm.12 This especially interests me because I often show gas discharge tubes in class and STEM outreach events. I can conceptually connect many of the gases to those found in the atmosphere. Though hydrogen is not present in high concentrations in our air, I have often included the gas because I find its glow rather striking and I encourage viewers to debate what color the gas looks like to them, Figure 6. (Some say pink, some say purple, but I often settle on magenta.) Now there is an opportunity to put more context on the gas glow for a few people. At recent STEM outreach events held after the eclipse, I have been able to connect the color of the little glowing Vernier discharge tube to the color of solar prominences nearly three times the size of the Earth.11
Figure 6. Reddish glow from a Vernier hydrogen gas discharge tube.
There has been much information made public before, during, and after the eclipse – certainly more than can be fit into this format. As noted above, my goal was to share a few thoughts about my eclipse experience from a chem/STEM perspective, and I hope you might have found something to connect to your classroom.
Safety
Use of lasers carries the risk of their intense light doing damage to objects. This not only includes light emitted directly from the laser but reflected light. Exercise extreme caution when working with lasers to avoid eye damage! Eclipse glasses with any damage to them are useless for viewing eclipses, so they must not be recycled after sustaining laser damage.
Acknowledgements
We thank Karl Jung for the solar array energy data and Rhiannon Davids and Kathleen Asmussen for their observations about the UV bead color changes. We also thank Karen, Kristine, and Katie Campbell for accompanying me on the eclipse trip. This work was supported by Bradley University and the Mund-Lagowski Department of Chemistry and Biochemistry with additional support from the Illinois Heartland Section of the American Chemical Society and the Illinois Space Grant Consortium.
References
- Great American Eclipse.com. Total solar eclipse 2024 US. https://www.greatamericaneclipse.com/april-8-2024 (accessed April 2024).
- Great American Eclipse.com. 2017 Total solar eclipse. https://www.greatamericaneclipse.com/best-places-to-view (accessed April 2024).
- Big Things Small Town. Big Things in a Small Town & Casey Chamber of Commerce. https://www.bigthingssmalltown.com/ (accessed April 2024).
- Dobrijevic, D. Great Space.com. 14 of the best total solar eclipse 2024 photos from our readers. https://www.space.com/best-total-solar-eclipse-2024-photos (accessed April 2024).
- Occupational Safety and Health Administration. H2S Safety and Health Hazards. https://www.osha.gov/etools/oil-and-gas/general-safety/h2s-monitoring (accessed April 2024).
- Campbell, D. J.; Wright, E. A.; Dayisi, M. O.; Hoehn, M. R.; Kennedy, B. F.; Maxfield, B. M. “Classroom Illustrations of Acidic Air Pollution Using Nylon Fabric.” J. Chem. Educ., 2011, 88, 387-391.
- Campbell, D. J. ChemEd Xchange. A Demo A Day III: Demonstrations and Props Used in My General Chemistry II Classes. https://www.chemedx.org/blog/demo-day-iii-demonstrations-and-props-used-... (accessed April 2024).
- Campbell, D. J. ChemEd Xchange. Photochromic glue and spring decorations. https://www.chemedx.org/blog/photochromic-glue-and-spring-decorations (blog post). (accessed April 2024).
- Bourner, L. K. Chemical & Engineering News. What are eclipse glasses, and how do they keep your eyes safe during an eclipse? https://cen.acs.org/safety/consumer-safety/What-are-eclipse-glasses-and-keep-eyes-safe/102/i10#:~:text=Many%20of%20the%20eclipse%20glasses,to%20the%20mix%2C%20he%20says (accessed April 2024).
- Lippincott, K. A.; Rosengarten, E. A.; Sengupta, A.; Campbell, D. J. “Using Polymers and Pigments to Produce Laser Interference Rings.” J. Chem. Educ., 2019, 96, 2553-2559.
- Krouse, P. Cleveland.com. What was that red thing extending from the bottom of Monday’s total solar eclipse? https://www.cleveland.com/news/2024/04/what-was-that-red-thing-extending... (accessed April 2024).
- Wikipedia.com. Hydrogen-alpha. https://en.wikipedia.org/wiki/Hydrogen-alpha (accessed April 2024).
Safety
General Safety
General Safety
For Laboratory Work: Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).
For Demonstrations: Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.
Other Safety resources
RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies
NGSS
Students who demonstrate understanding can develop a model based on evidence to illustrate the life span of the sun and the role of nuclear fusion in the sun’s core to release energy that eventually reaches Earth in the form of radiation.
*More information about this category of NGSS can be found at https://www.nextgenscience.org/dci-arrangement/hs-ess1-earths-place-univ....
Students who demonstrate understanding can develop a model based on evidence to illustrate the life span of the sun and the role of nuclear fusion in the sun’s core to release energy that eventually reaches Earth in the form of radiation.
Assessment does not include details of the atomic and sub-atomic processes involved with the sun’s nuclear fusion.
Emphasis is on the energy transfer mechanisms that allow energy from nuclear fusion in the sun’s core to reach Earth. Examples of evidence for the model include observations of the masses and lifetimes of other stars, as well as the ways that the sun’s radiation varies due to sudden solar flares (“space weather”), the 11- year sunspot cycle, and non-cyclic variations over centuries.