Solar Eclipse Duration Calculator
Estimate how long totality or partial coverage will last at your location during a solar eclipse. Enter the eclipse path width, Moon shadow speed, and your latitude to get duration in seconds.
About this calculator
The duration of a solar eclipse at any point depends on how long the Moon's shadow takes to sweep across that location. For a total eclipse, the duration in seconds is: Duration = (pathWidth / moonSpeed) × 3600 × cos(latitude × π / 180). The cosine factor corrects for the fact that the shadow path crosses latitude lines at an angle, making the effective path shorter at higher latitudes. For a partial eclipse the formula simplifies to (pathWidth / moonSpeed) × 1800, and for an annular eclipse it uses × 2800. Path width is measured in km, Moon shadow speed in km/h, and the result is in seconds. Totality can last anywhere from a fraction of a second at the path edges to over 7 minutes near the central line.
How to use
Suppose you are at latitude 40° N watching a total solar eclipse. The path width is 160 km and the Moon's shadow is moving at 2,800 km/h. Step 1: Duration = (160 / 2800) × 3600 × cos(40° × π / 180). Step 2: 160 / 2800 = 0.05714 hours. Step 3: 0.05714 × 3600 = 205.7 seconds. Step 4: cos(40°) ≈ 0.766. Step 5: 205.7 × 0.766 ≈ 157.6 seconds, or about 2 minutes 38 seconds of totality. If the eclipse were partial under the same conditions, duration = (160 / 2800) × 1800 ≈ 102.9 seconds.
Frequently asked questions
Why is totality shorter at higher latitudes during a solar eclipse?
The Moon's shadow travels roughly parallel to the equator, so its path cuts across lines of latitude at an angle. At higher latitudes, the shadow's circular footprint intersects your position on a chord rather than a diameter, effectively reducing the distance the shadow sweeps over you. The cosine correction in the formula accounts for this geometric shortening — at 60° latitude, totality lasts only cos(60°) = 0.5 times as long as it would on the central line at the equator with the same path width.
What is the difference between a total, partial, and annular solar eclipse?
In a total solar eclipse, the Moon is close enough to Earth that it completely covers the Sun's disk, producing a brief period of totality where the corona becomes visible and the sky darkens dramatically. In a partial eclipse, only a portion of the Sun is covered, and totality never occurs at your location. In an annular eclipse, the Moon is near apogee (farthest from Earth) and appears slightly smaller than the Sun, leaving a bright 'ring of fire' around the Moon's silhouette — totality never occurs even on the central line. Each type produces a different duration formula because the geometry of the shadow coverage differs.
How fast does the Moon's shadow travel across Earth's surface?
The Moon's umbral shadow typically moves between about 1,700 km/h and 3,600 km/h across Earth's surface, depending on the geometry of the eclipse. Near the equator and when the Moon is directly overhead, the shadow moves more slowly, which is why equatorial eclipses can last close to the theoretical maximum of about 7 minutes 32 seconds. Near the edges of the path, or at higher latitudes where Earth's curved surface moves away from the shadow's direction of travel, the apparent speed increases significantly and totality becomes much shorter.