Lunar Eclipse and the Blood Moon Phenomenon

Syllabus: Geography (UPSC Prelims)
Source: HT

Context:

On 7 September 2025, a total lunar eclipse will be visible in India. During this event, the moon will look dark red because Earth’s shadow covers it.

What is a Blood Moon?

A blood moon happens during a total lunar eclipse when the moon looks reddish instead of its usual white colour.

How Does It Happen?

• Earth moves between the sun and the moon.
• The direct sunlight is blocked by Earth’s shadow.
• Some sunlight passes through Earth’s atmosphere and bends toward the moon.
• The atmosphere filters out blue light, allowing red light to reach the moon, giving it a copper-red colour.

Key Features

• The red colour depends on the amount of dust, smoke, or particles in Earth’s atmosphere.
• The phenomenon is caused by Rayleigh scattering – the same process that makes the sky appear blue.
• The eclipse can be seen from a wide area where the moon is above the horizon.
• It is a completely natural event and can be predicted accurately.
• The eclipse can last for several hours.

Importance

• It helps scientists learn about Earth’s atmosphere, such as the presence of dust, volcanic ash, and pollution.
• It is valuable for astronomy and educating the public about space.
• Many cultures view the blood moon as having spiritual or cultural significance.