Earth’s Umbra creates rare blue hue in stunning Blood Moon eclipse, NASA reveals image

The Umbra of Earth (Image: Wang Letian/NASA)

On the night of September 7 and 8, skywatchers worldwide witnessed a rare celestial event. The Full Moon passed near the centre of Earth’s dark umbral cone. This created a slow-moving total lunar eclipse visible from many parts of the planet.

What Is the Earth’s Umbra?
The umbra is the inner, dark shadow of Earth. Conical in shape, it reaches deep into space. Its circular cross-section is best seen in a lunar eclipse. As the Moon moved through the shadow, it gradually darkened.

A timelapse composite image from Zhangjiakou City, China, shows the eclipse clearly. The pictures progress from left to right, revealing the umbra’s curved shadow. During totality, the Moon was fully inside Earth’s umbra for about 83 minutes.

Why Does the Moon Turn Red and Blue?
Sunlight refracted by Earth's atmosphere provides the Moon with a reddish hue. This is due to the fact that the atmosphere refracts and scatters light into the umbra. Surprisingly, at the edge of the umbra, the limb of the Moon was clearly blue. This blue light is due to the sunlight that has passed through the upper stratosphere. Ozone in the atmosphere scatters red light and lets blue light pass.

Millions of people across Antarctica, Australia, Asia, Europe, and Africa caught a glimpse of this slow-moving shadow. Scientists say the eclipse offers a rare chance to study Earth’s atmosphere in action. The gradual movement of the shadow reminded spectators of the enormity of space and the subtle forces involved.