Skywatchers are in for an ecliptic encore tomorrow night (Aug. 27 to 28) as a very deep partial lunar eclipse promises to turn the full moon coppery red.

As the full moon slides into Earth's shadow, it will cast an eerie red glow over 96% of the lunar surface. In North and South America, every stage of the eclipse will be visible in the night sky, beginning at 9:23 p.m. EDT on Thursday night (Aug. 27), ending around 3 a.m. Friday (Aug. 28), and peaking just after midnight. Meanwhile in Europe, the eclipse will occur just before dawn as the moon sinks below the horizon.

The moon won't fall totally under Earth's shadow, so we can't officially call it a "blood moon," but it will be the deepest lunar eclipse anywhere in the world until the next total lunar eclipse on Dec. 31, 2028.

Why does the moon turn red during a lunar eclipse?

A lunar eclipse happens when the moon passes directly behind Earth and falls into its shadow. But instead of going completely dark, the moon turns a deep shade of coppery red. This is because of the way Earth's atmosphere absorbs and bends light.

Sunlight is made up of a spectrum of colors. The blue and yellow parts of this spectrum are absorbed by Earth's atmosphere. But red light is bent, or refracted, by our planet's atmosphere and directed toward the moon, lighting it up like a blood-red flashlight beam, according to the European Space Agency.

The exact shade of red depends on what else is going on in Earth's atmosphere at the time. For example, volcanic ash and desert dust can significantly darken a lunar eclipse.

Unlike with a solar eclipse, you don't need eclipse glasses to safely see a lunar eclipse.

While the partial eclipse will be visible to the naked eye, even better views are possible if you use one of the best telescopes, best smart telescopes or best stargazing binoculars. If you're looking to photograph the moon, check out our picks for the best astrophotography cameras to capture the best shots of the lunar eclipse.