The total solar eclipse of August 12, 2026
Educator answer key: the eclipse of August 12, 2026
Open the simulator at:
Values below come from NASA's public tables, rounded. The simulator agrees with them to within about two minutes on times. Grade classification, comparison, and reasoning; treat copied digits as evidence, not as the graded content.
Part 1: Predict
Expected: Much narrower than the Moon. The dark core (umbra) is about 294 km wide at the deepest point of this eclipse; the Moon is 3,474 km wide.
Look for: Look for the idea that the Sun is a large light source, so the full shadow shrinks to a narrow tip by the time it reaches Earth. Any phrasing that captures "big light source, shrinking shadow" counts.
Common errors: Most learners predict Moon-sized. That is the misconception this investigation targets, so a wrong prediction costs nothing. What matters is whether Part 5 shows they updated.
Part 2: Watch the shadow
Expected: Two parts: a small dark core (the umbra) and a wide pale fringe (the penumbra). The core is roughly a third as wide as Spain.
Look for: Accept anything from "a few hundred kilometers" to "much smaller than any country it crosses". The point is the contrast between the two scales.
Common errors: Some learners describe the penumbra as "the shadow" and miss the core entirely. Send them back to look for the darkest spot.
Part 3: Compare three places
Expected: Reykjavik: total, 100 percent, maximum about 17:48 UTC. Madrid: partial, about 99 percent, maximum about 18:32 UTC. London: partial, about 91 percent, maximum about 18:13 UTC.
Look for: Sun height: grade the comparison, not the digits. Reykjavik sees the Sun clearly higher; in Spain it is close to the horizon. Times within a couple of minutes of the values above are correct.
Common errors: Mixing up coverage with "how dark it gets". Coverage is the fraction of the Sun's disc that is hidden; the sky in Madrid stays bright anyway.
Part 4: Stand in the shadow
Expected: Any of: the sky turned dark in the middle of the day; a glowing ring (the corona) appeared around a black disc; the light vanished and returned within minutes.
Look for: The Madrid view never shows a dark sky or the corona. That contrast is the evidence Part 5 needs.
Common errors: Vague answers like "it looked different". Ask for one specific thing that was present in one view and absent in the other.
Part 5: Explain
Expected: Disagree. Evidence: Madrid keeps about one percent of the Sun uncovered, its sky stays bright, and no corona appears; Zaragoza gets about two minutes of darkness and a visible corona. Reasoning: the Sun is so bright that the last one percent decides the whole experience.
Look for: A strong answer uses the recorded evidence, not just the numbers. Claim, evidence, reasoning in any order is fine.
Common errors: Agreeing because 99 is numerically close to 100. Push those learners to compare the two sky views they saw, not the two percentages they wrote down.
Model limits
Do not grade against seconds-precision times. The simulator and NASA's tables can differ by up to about two minutes, and both describe geometry, not weather.
Safety
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.