Savor it while you can, because the moon is creeping away from Earth — at about 3.8 centimeters (1.5 inches) each year, according to NASA. That’s the rate fingernails grow. When the moon’s average distance from Earth increases by 14,600 miles, it will be too far to fully cover the sun from Earth’s perspective.

The cosmic coincidence that gives us total solar eclipses isn’t permanent. The Moon is ever so slowly moving away from our planet at rate of about 1.5 inches (3.8 centimeters) per year. As it recedes, its average apparent diameter shrinks. Eventually, the Moon will never be large enough to completely cover the Sun, and total eclipses will no longer be visible from Earth’s surface.

And when might this sad prospect come to pass? The calculation is not precise — there are many unknowns such as whether the lunar retreat will continue at a constant rate and whether the solar diameter will remain stable over a long period of time. Still, about a billion years from now, give or take a few hundred million years, the surface of Earth will experience its final total eclipse of the Sun. Annular eclipses will continue to occur, though the percentage of the solar surface hidden by the Moon will gradually decrease.

So, when you stand in the lunar shadow watching the Moon pass between Earth and the Sun, revel in the knowledge that you are witnessing one of the most unusual and spectacular events in the cosmos.