The Rare Celestial Event That Will Eventually Disappear For Earth

There are many types of eclipses, but the kind that really excites people, the kind that makes headlines on the news, is a total solar eclipse. In a total solar eclipse, the orbits of the Earth, moon, and sun align perfectly, so that, viewed from Earth, the moon appears to block out the sun, shrouding everything in its path in darkness. It is a dramatic occurrence, one that made ancient civilizations quake with fear, but the Earth is only in for a limited number of these total eclipses.

Solar eclipses occur much more frequently than you might think, roughly every year and a half. However, they feel much rarer because each eclipse can only be seen from a limited area on Earth known as the path of totality. The frequency at which any given location falls into the path of totality for a solar eclipse is much, much rarer than once every year and a half. In the northern hemisphere, it only happens once every 350 years on average, and in the southern hemisphere, it's only once every 450 years.

The chances of a solar eclipse being visible from your own home are exceedingly rare, and yet, they are becoming even rarer. Slowly but surely, the moon is drifting further away from the Earth, and eventually, it won't be large enough from our perspective to block out the sun. Thankfully, that won't happen anytime soon.

Total solar eclipses are only possible because the moon and the sun appear to be roughly the same size from our perspective on Earth. That doesn't always happen though. The moon has an elliptical orbit around Earth, so its distance from us varies. Sometimes, the moon is too far away to completely cover the sun, leaving a broad ring of light around it. This is called an annular solar eclipse, and eventually, it will be the only kind of solar eclipse that occurs.

The moon is currently drifting away from Earth at a rate of roughly 1.5 inches every year. This is due to the gravitational forces that our planet and its satellite exert on each other. The moon's gravity causes ocean tides on Earth, and those tides gradually slow down the rate of Earth's rotation. Before the moon formed, a day on Earth lasted only five hours, so you can see how dramatic the effect has been. In order to make up for the angular momentum lost by Earth's orbit slowing down, the moon is increasing the distance between us.

As the moon drifts further away, annular eclipses will become more frequent until there are no total eclipses at all. That won't happen for around 700 million more years though. The moon will continue to drift away from Earth for about 5 billion years, but then, the sun will die. Not exactly a happy ending, but at least we won't be here for it.