Lunar eclipses happen when the moon, Earth, and sun align just so. The Earth casts a shadow that can partially or totally blot out the moon.

SEE ALSO: Solar eclipse stamp changes when you touch it They've launched a special simulator, part of the broader Eclipse Megamovie Project, which will give a glimpse of what to expect on August 21.

Earth’s shadow will block most of the light that illuminates the lunar surface, creating what is known as a blood moon.