On Oct. 8, many Americans witnessed the second total eclipse of the year – with a twist. An extremely rare cosmic sight known as the “blood moon” lit up the sky early Wednesday morning. This phenomenon happens when the total eclipse of the moon is simultaneous with the sun rising, giving the moon a red tint, which celestial geometry says cannot happen.

A lunar eclipse occurs when the sun and the moon are perfectly align – exactly 180 degrees apart in the sky, known as a “syzygy.” The blood moon’s occurrence seems impossible, but was actually created of the Earth’s atmosphere. The images of the sun and the moon were lifted above the horizon by atmospheric refraction, which allows observers to see the sun several minutes before it has risen, and the moon for several minutes before it has set.

The eclipse began at 4:15 a.m. Central Daylight Time, which gave the moon a slight orange tint. The total eclipse began about an hour later, gradually turning the moon to a dark red color. From the east coast, the moon set while the eclipse was in progress, but western half of the country was able to see the entire thing.

Depending on the location, weather, and clarity of the sky, observers had roughly 10 to 15 minutes to see this sensation before sunrise while the moon was still high enough to be visible.