The total solar eclipse of August 12, 2026
Facilitator guide: the August 12, 2026 total solar eclipse
Open the simulator at:
Objectives
- Learners can explain why totality is a narrow strip while the partial eclipse covers most of a continent.
- Learners can read classification, coverage, UTC contact times, and Sun altitude for a location.
- Learners can explain why a 99 percent partial eclipse is not almost the same as totality.
- Learners can state the eye-safety rules.
Prior knowledge
Learners should know that the Moon orbits Earth about once a month, and that the Sun is much larger than the Moon but much farther away. Nothing else is required.
Preparation
- Open the simulator once on the machine you will use, with the link from this guide. The scenario starts above Earth a few minutes before the shadow arrives.
- For the classroom version, print one student sheet per learner.
- Print the answer key for yourself. Keep it off the projector.
- If the machine is slow, close other tabs. Everything runs in the browser; no installation or account is needed.
Materials
A computer or tablet with a modern browser and, ideally, a projector. Printed student sheets and pens for the classroom version. Optional: one pair of eclipse glasses to pass around as a prop.
Exhibition script (10 to 15 minutes)
Take predictions (2 min)
Ask: "The Moon is about 3,500 km wide. On August 12 it will block the Sun and cast a shadow on Earth. How wide is that shadow?" Take three or four answers. Most people say Moon-sized. Do not correct anyone yet.
Watch the globe (3 min)
Start the scenario and let the shadow cross Earth. Point out the two parts: the wide pale region and the small dark core. Ask what they notice about the size of the core. It is a few hundred kilometers, far smaller than the Moon.
Compare two places (3 min)
Open the location explorer. Show Reykjavik: total, 100 percent. Show Madrid: partial, about 99 percent. Ask: "99 percent. Is that basically the same thing?" Take answers, then move on without resolving it.
Stand in totality (4 min)
Use View from here at Reykjavik and let time run: partial phase, totality, and the light coming back. Stay quiet through totality; the moment carries itself. Then show the same view from Madrid, where the sky never darkens and no corona appears. Now resolve the question: the last one percent is the whole show.
Close with safety (2 min)
Show the safety block and say the two core rules aloud: only ISO 12312-2 glasses or projection during partial phases, and direct viewing only during full totality. Point visitors to the printed page or the public link to check their own town.
Classroom activity (45 minutes)
Individual prediction (5 min)
Learners fill in Part 1 of the sheet: predicted shadow width, with one sentence of reasoning. No discussion yet.
Globe observation (10 min)
Run the scenario on the projector or on group machines. Learners complete Part 2: describe the two shadow parts and estimate the size of the dark core.
Location comparison in groups (10 min)
Groups use the location explorer to fill the Part 3 table for Reykjavik, Madrid, and London, then use View from here at Reykjavik and Madrid for Part 4.
Explanation and discussion (10 min)
Collect observations. Build the explanation together: the Sun is a wide light source, so the full shadow narrows to a small tip at Earth's distance. Then contrast the two sky views and ask why one percent matters so much.
Plan the real event (5 min)
Ask: "What would we need to watch this safely from here?" Learners name the safety equipment and check what coverage your town gets.
Exit question (5 min)
Part 5 of the sheet: "A friend says watching from Madrid is basically the same as from Zaragoza. What do you tell them?" Collect the sheets.
Questions to ask
- How wide is the dark core compared to the Moon itself?
- Much narrower. The core is a few hundred kilometers; the Moon is 3,474 km wide.
- Who sees a partial eclipse at the moment someone in Iceland sees totality?
- Everyone standing in the wide penumbra at that moment, which covers a large part of Europe and the North Atlantic.
- Why does the location card show the Sun's height?
- Because it changes what you can see. In Spain the Sun is close to the horizon during the eclipse, so you need a clear view to the west.
Common misconceptions
- The shadow should be Moon-sized.
- The Sun is a wide light source, not a point. The full shadow narrows to a cone and only its tip reaches Earth.
- 99 percent coverage is almost totality.
- The remaining one percent keeps the sky bright and hides the corona. Totality is a different experience, not a slightly stronger one.
- There should be an eclipse every new moon.
- The Moon's orbit is tilted about five degrees, so the shadow usually misses Earth.
- Eclipse glasses are only needed during totality.
- It is the reverse. Totality is the only phase you may watch without protection, and only from inside the strip.
Troubleshooting
- The scenario did not load: check that the link ends with ?preset=solar-eclipse-2026.
- Learners ran time past the eclipse: reload the scenario, or set the date back to August 12, 2026, 17:35 UTC with the date control.
- The simulation stutters: close other tabs and browser windows; the eclipse scene is one of the heavier views.
Accessibility
The location explorer presents everything as text and numbers, so a learner who cannot see the globe can still complete the whole table. The shadow is a brightness difference, not a color difference, so color vision is not required. All values on the cards can be read aloud directly.
Model limits
Luna computes the eclipse from real Sun and Moon geometry. Contact times can differ from NASA's published tables by up to about two minutes, and the exact edge of the totality path by a few kilometers. Luna does not model weather or local clock time; all times are UTC. If learners plan real observations near the path edge, point them to a dedicated eclipse map.
Safety
The safety block on the student sheet is required reading before any discussion of real observation. In the exhibition version, say the rules aloud; do not only point at them.
Watching the real eclipse safely
Luna is a simulator, not local observing advice. The guidance below is NASA's, from its eclipse safety page.
- During every partial phase, look at the Sun only through eclipse glasses or a handheld solar viewer that meets the ISO 12312-2 standard, or use an indirect method such as a pinhole projector.
- **Ordinary sunglasses are not safe, no matter how dark.**
- Never look at the Sun through a camera, telescope, or binoculars while wearing eclipse glasses. Concentrated light burns through the filter and injures your eye. Optical equipment needs a proper solar filter mounted on the front.
- On totality, NASA writes: “You can view the eclipse directly without proper eye protection only when the Moon completely obscures the Sun’s bright face, during the brief and spectacular period known as totality. (You’ll know it’s safe when you can no longer see any part of the Sun through eclipse glasses or a solar viewer.)” Read NASA's full guidance before the day.
- With a pinhole projector, look at the projected image on the ground or wall. Never look through the pinhole at the Sun.
Answer key
The answer key is a separate page written for educators. Keep it off the projector and out of the printed student set.