Solar Physics
Solar Eclipse
When the Moon passes between Sun and Earth — total, annular, or partial
A solar eclipse occurs when the Moon passes between the Sun and Earth, casting its shadow on Earth's surface. Total eclipse — Moon fully covers Sun's disk; corona becomes visible; only along narrow path (~100 km wide). Annular — Moon farther from Earth, doesn't fully cover; "ring of fire." Partial — outer shadow (penumbra). Lunar coincidence: Sun is ~400× larger but ~400× farther — angular sizes nearly match, enabling totality. Without this coincidence, no totality possible.
- Solar diameter1.39 million km (~400× Moon)
- Sun-Earth distance149.6 million km (~400× Moon-Earth)
- Total path width~100-300 km wide
- Totality durationUp to 7.5 minutes (rare); typically 2-3 min
- Eclipse typesTotal, annular, partial, hybrid
- Eclipses per year2-5 (most are partial; total rare from any location)
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
Why eclipses matter
- Solar physics. Best chance to see corona without coronagraph.
- General relativity test. 1919 eclipse confirmed Einstein.
- Public engagement. Most-watched astronomical events.
- Animal behavior. Studies during totality (animals confused by sudden darkness).
- Atmospheric science. Brief temperature, wind changes provide data.
- Historical record. Eclipses date ancient texts (e.g., Herodotus's eclipse).
- Anniversaries. 2026 eclipses planned years out.
Common misconceptions
- Eclipse is dangerous to view always. Only direct sun is dangerous; totality is safe to view briefly.
- Total eclipse happens monthly. Tilted orbit makes new moon usually miss the sun.
- Same place gets totality often. Once per ~375 years for any specific spot.
- Annular is similar to total. Quite different — bright ring is still very bright.
- Corona is created during eclipse. Always present; just blocked by sun's brightness normally.
- Moon is always going to give us eclipses. Receding — totality ends in ~600 Myr.
Frequently asked questions
Why aren't there eclipses every month?
Moon's orbit is tilted ~5° to Earth's orbit around Sun. New Moon usually passes above or below the Sun's disk from Earth's view. Only when New Moon happens near a node (where orbits intersect) does an eclipse occur. These "eclipse seasons" happen ~twice/year, each lasting ~34 days.
What's the difference between total and annular?
Moon's distance from Earth varies (perigee 363,000 km to apogee 405,000 km). At perigee, Moon appears slightly larger than Sun → fully covers it (total). At apogee, Moon appears slightly smaller → leaves "ring of fire" around edge (annular). Same alignment, different distances.
Why is total eclipse so rare?
Total path is narrow (~100 km wide) because Moon's umbra is small. Plus Earth's surface is mostly ocean. Any specific location sees totality once per ~375 years on average. Path moves across Earth — observers chase eclipses to specific locations.
What can you see during totality?
Sun's corona — million-degree atmosphere normally invisible. Solar prominences — pink loops of plasma. Diamond ring effect — last beam through lunar valleys. Bailey's beads — chain of bright points. Stars and planets become visible. Temperature drops noticeably. 360° sunset on horizon.
How is annular eclipse seen?
"Ring of fire" — bright sun visible around lunar disk. Cannot view safely with naked eye even at maximum (sun never fully covered). Solar filters required throughout. Annular eclipse less spectacular than total but still impressive.
Why is the angular coincidence remarkable?
Sun is ~400× wider than Moon AND ~400× farther — so angular size matches. This is coincidence (not physics). Earth is the only known place where total eclipses occur as we see them. Moon is slowly receding (~3.8 cm/year) — in ~600 million years, no more totality possible.
How are eclipses predicted?
With great precision. Saros cycle — 18 years 11 days between similar eclipses. Lunar/solar orbits well-modeled. NASA publishes eclipse paths to ±1 minute timing accuracy decades ahead. Eclipse chasers can plan trips with confidence. Future eclipses fully mapped.