Why can a total solar eclipse be seen from only a narrow path on Earth?

A total solar eclipse is visible from only a narrow path on Earth because of the specific nature of the Moon's shadow. When the Moon passes between the Sun and Earth, it casts a shadow consisting of two primary regions: the penumbra and the umbra.12

The umbra is a narrow, cone-shaped region of total shadow where no direct sunlight penetrates. Because the Moon is much smaller than Earth, this umbral cone is quite narrow by the time it reaches the Earth's surface, often spanning only about 150 km (90 miles) in width. A total solar eclipse can only be observed by those positioned within this specific, narrow strip of land or sea as the shadow sweeps across the planet.123

Observers located outside this path but within the much larger region covered by the penumbra will experience only a partial eclipse, as the Moon appears to cover only a portion of the Sun's disk.12