Astronomy Fun Fact #92
Total solar eclipses are possible because the apparent size of the Moon on the sky is bigger than the apparent size of the Sun. Both take up about .5 degrees on the sky.
But the Moon is moving about 1.5 inches away from the Earth every single year, so it's apparent size is getting smaller over time. And the Sun is getting slightly bigger over time as it fuses more and more hydrogen into helium in its core, so its apparent size is getting bigger.
That means that there will come a day when it's impossible to see a total solar eclipse from Earth. NASA predicts that that day will happen in 563 million years, but Belgian astronomer Jean Meeus predicts that the last total solar eclipse will happen in about 1.2 billion years because the orbits of the Moon and Earth will change. But he says that that last eclipse will only last for about a second.