Why the moon turns red during eclipses and how Earth's shadow creates it

By Vivek Dubey

CNBC-TV18.com

Published Sept 18, 2024

Umbra Explained

The umbra is the darkest part of Earth's shadow. During a partial lunar eclipse, only part of the Moon moves through this region, causing visible darkening.

Penumbra Overview

The penumbra is the lighter outer shadow cast by Earth. The Moon's surface may appear dimmer when it enters this shadow, especially in a penumbral eclipse.

Partial Eclipse Process

In a partial lunar eclipse, Earth blocks part of the sunlight, causing only a portion of the Moon to move into the umbra. The Moon’s surface partially darkens.

Total Eclipse Process

A total lunar eclipse occurs when the entire Moon enters Earth's umbra, completely blocking sunlight. The Moon appears fully darkened in this alignment.

Supermoon Eclipse

A supermoon eclipse occurs during a total lunar eclipse when the Moon is closest to Earth. It looks larger and slightly brighter, earning the "supermoon" name.

Penumbral Eclipse Details

In a penumbral lunar eclipse, the Moon passes entirely through Earth's penumbra. The change is subtle, only affecting the Moon’s brightness, not its colour.

Why the Moon Turns Red

During a total eclipse, Earth's atmosphere filters out most colours of light except red. This light reaches the Moon, causing it to appear reddish.

Light Filtering Effect

As sunlight passes through Earth’s atmosphere, shorter wavelengths like green and violet scatter. Only red wavelengths reach the Moon, giving it a red glow.