Back to Dave's Astrophotos

We earthlings are incredibly lucky to have a moon which is about the same apparent size as our sun. To put it in perspective, the following images (source unknown) show the relative sizes of the planets in our solar system. Note: in terms of size, our moon is about halfway between Mercury and Pluto.

Although the sun's diameter is about 400 times bigger than the moon's, it happens to be about 400 times farther away. Due to irregularities in the orbits of the earth and moon, the moon ranges from appearing slightly smaller to slightly larger than the sun. It is only in the latter case that total eclipses may occur. And because the moon's apparent size is only slightly larger than the sun's, we are treated to spectacular views of the sun's corona and prominences during totality.

It wasn't always so, as the moon has been slowly receding from the earth for billions of years. In the distant past the moon always appeared much larger than the sun, obscuring the sun's peripheral features during totality. A billion years from now, give or take, the final total eclipse will occur.

It is possible, but horribly complicated, to calculate eclipse patterns, paths, and local circumstances. Fortunately, we have people like Fred Espenak (Mr Eclipse) and places like Eclipses Online to provide this information on the Internet. Looking at these sites, one sees that total solar eclipses, especially those lasting longer than several minutes, are pretty rare.

Amazingly, three total eclipses exceeding seven minutes occurred in the 20th century, in 1937, 1955, and 1973. The previous such event occurred in 1098, and the next occurs in 2150. Even more amazing (cue Twilight Zone music), my favorite astrophotographer was born on the day of the 1955 eclipse, although not in the actual moon's shadow. That would have been almost freaky!