If you’ve ever watched the sun glint in a lake, you’ve probably noticed that it moves from east to west. It’s the same thing that happens when the moon passes in front of the sun, casting a shadow on Earth.

The reason that the path of a total solar eclipse starts in the west and ends in the east is a bit more complex than just the fact that the Earth spins counterclockwise as it orbits the sun. When viewed from outside space, the moon also appears to move in a counterclockwise direction as it orbits the Earth.

A symbolic orbital diagram from the view of a planet (like Earth) with the Sun and Moon projected upon it shows the two nodes, or points of no return, where the moon can be seen to eclipse the sun. The nodes shift (precess) from west to east over time, which means that every few years, a new path for an eclipse occurs.

This August 21, a total lunar eclipse will be visible across the United States. The moon will rise in the east-northeast, and a high location or a clear horizon should help viewers in most parts of the country see the event.

Whether you’re in the country or abroad, you don’t need any special equipment to see a total lunar eclipse. But binoculars and a telescope can enhance your viewing experience, and it’s best to avoid bright lights to see the red color of the moon’s shadow better.