A total lunar eclipse happens when the moon moves into Earth's darkest shadow, the umbra.
The night sky offers moments that feel otherworldly and unforgettable. One of them is the total lunar eclipse, in which the full moon darkens in colour and reddens.
What does happen during a total lunar eclipse?
A total lunar eclipse happens when the moon moves into Earth's darkest shadow, the umbra. Rather than disappearing into blackness, the surface turns to red.
The sight is so striking that many call it a "blood moon". Viewers can watch the moon turn from grey to copper and crimson before it slowly brightens again. According to the National Weather Service, totality may last from thirty minutes to over an hour.
The colour change is caused by Earth's atmosphere. As sunlight passes through, shorter blue wavelengths scatter while red and orange travel more easily. That light is bent and projected onto the moon. The effect is similar to sunsets, when the sky glows with orange and pink tones. NASA explains that during totality it looks as if the world's sunrises and sunsets are cast on the moon.
Are there different kinds of lunar eclipses?
Yes, there are three kinds. A penumbral eclipse occurs when the moon crosses into Earth's weak outer shadow. It only faintly dims and is difficult to see. A partial eclipse takes place when a portion of the moon crosses into the umbra. The shadowed area can become red, though much of the surface remains light. Only in a total eclipse does the entire lunar face glow clearly red, because the whole moon moves inside the umbra.
The exact colour depends on conditions in Earth's atmosphere. Rayleigh scattering explains why the light is red, but dust, ash, clouds and water droplets change the shade. At times the moon may glow orange or copper, at others deep red or even brown. Volcanic eruptions and misty skies can make the moon appear darker, while clearer air makes it brighter. The appearance also shifts as different parts of the moon pass through the shadow's centre.