Caption: An animation of the eclipse path of the Solar eclipse of August 11, 1999 which was a total solar eclipse.

Features:

1. Note that the Earth is NOT rotating in the animation. So the observers---us that is---are NOT rotating either. We are observing from the zenith of somewhere in or near Greece.

2. Note that the Moon's umbra starts and ends its eclipse path on the Earth's terminator. It always must do this in total solar eclipses since as lunar umbra travels through space it touches down and leaves at the Earth's terminator.

   However, in a hybrid solar eclipse the umbra does NOT touch the Earth's surface during its annular solar eclipse phase, and so the umbra may NOT start or end on the Earth's terminator in hybrid solar eclipses.

3. Eclipse paths are almost always curvy on the Earth's surface (as illustrated in the animation) due to the curvature of said surface and the varying height of the Moon above the ecliptic plane. Calculating eclipse paths is a complicated process.

   However, during the relatively short time of a solar eclipse, the Moon's path in space is nearly a straight line perpendicular to the Earth-Sun line

4. The umbra always moves eastward on Eclipse paths . This is Moon and its shadow, the umbra) move eastward in space at an average speed of 1.022 km/s (see Wikipedia: Moon: Table; Moon's orbit; Wikpedia: The Moon's mean orbital speed = 1.022 km/s) and upper limit on the Earth's speed eastward is the Earth's equatorial Earth's equatorial rotational speed = 0.4651 km/s), and so the Moon wins the race to the east.

   In other words, NO place on Earth can keep up with umbra: the umbra must move east.

   However, counterfactually if the Moon moved slower than the Earth's equatorial rotational speed = 0.4651 km/s, the umbra would have to move west sometimes. The lower the latitude (i.e., the closer to the equator), the more easily westward could be arranged.

   Super counterfactually if the Moon were at rest on the Earth-Sun center-to-center line, then the umbra would sweep west (from an fixed Earth view) over the subsolar point (which is always in the tropics) perpetually as the Earth rotates east relative to the observable universe.

5. The upper limit on how long the umbra can stay on Earth is about:

           amount     diameter      2*6378.1370 km
     t =  -------- = ------------ = --------------  = 12480 s = 3.467 hours = 3.5 hours .
           rate       Moon speed    1.022 km/s 

   (see Wikipedia: Earth equatorial radius R_eq_⊕ = 6378.1370 km; Wikpedia: The Moon's mean orbital speed = 1.022 km/s).

   Most Earth contact times for the umbra will be less than 3.5 hours since the umbra will move along a chord that is NOT a diameter on the disk of the Earth.

   The Earth contact time for the Solar eclipse of August 11, 1999 was 3.1 hours which is close to maximal which is consistent with the eclipse path being close to a diameter as the animation shows.

6. The lower limit for the Earth contact time is zero which occurs for the umbra just grazing the Earth's limb.

7. EOF