The Mystery of the Red and Non-Red Halves of the Moon During a Lunar Eclipse

Have you ever marveled at the full moon during a lunar eclipse, noticing it takes on a breathtakingly red hue in parts while remaining almost unaltered in others? This article aims to unravel the mystery behind this fascinating celestial phenomenon.

The Role of Earth's Atmosphere

The apparent red or orange color changes in the moon during both its regular and eclipsed phases are due to the Earth's atmosphere. When the sun dips low on the horizon, the light passes through more of the atmosphere, causing all colors but red to be filtered out. This is why the sun and moon can appear red when they are near the horizon.

The Mechanism of a Lunar Eclipse

During a lunar eclipse, the Moon moves into the Earth's shadow. This shadow has two distinct parts: the outer penumbra and the inner umbra.

Penumbra: In this outer shadow, the Earth only partly blocks the sun, so some direct sunlight still reaches the Moon. This area may appear slightly dim or even unaltered, especially when viewed from certain angles. Umbra: The inner shadow where the Earth completely blocks the sun's direct light. Despite this complete block, the Moon does receive some light. This light is diffused and scattered around the Earth, especially from the edges of the Earth's curvature, where the Sun is rising or setting.

One might wonder, why this scattered light appears red. The answer lies in the Earth's atmosphere. Red light is refracted and scattered more easily by the Earth's air molecules, making the light that reaches the Moon more reddish. Interestingly, the color we see during a lunar eclipse can vary, influenced by factors like atmospheric pollution and dust.

Real vs. Superstition

The so-called “blood red moon” is a term rooted in myth and superstition. Astronomers categorically do not consider it a real phenomenon with any specific astrological significance. It is purely a result of optical and atmospheric effects.

Shooting the Colors: Capturing the Eclipse

Photographing the red hues during a lunar eclipse can be challenging due to the dynamic range, but it can also lead to incredible visual documentation. Here is an example of a high dynamic range (HDR) image of the lunar eclipse, which captures the true colors of the Earth's umbra in stunning detail:

Lunar Eclipse HDR U2

A Controversial Example

Recently, I witnessed a similar situation in North California, where serious wildfires caused a dramatic red-tinted sky during the day and moonrise. The Earth's atmosphere, filled with particulate matter, not only added to the sky's vivid colors but also to the moon's unusual appearance.

So, if you ever come across a red or orange Moon during a lunar eclipse, remember, it's just the science of our atmosphere at work. Nothing to be scared of, just an amazing sight to behold!