The popular term “Blood Moon” is a dramatic, non-scientific descriptor for a total lunar eclipse. This astronomical event occurs when the Moon takes on a deep reddish-orange glow, a phenomenon that has captured human attention for millennia. The historical quest is to pinpoint when humankind first systematically observed and recorded this occurrence. The earliest verifiable records offer a direct link between modern astronomy and ancient civilizations.
Defining the Total Lunar Eclipse
A total lunar eclipse occurs when the Sun, Earth, and Moon align in a nearly perfect straight line. In this configuration, the Earth passes directly between the Sun and the Moon, casting a shadow that engulfs the Moon. The Earth’s shadow has two parts: the outer, lighter penumbra, and the inner, darker umbra.
For the eclipse to be total, the Moon must pass completely into the umbra, the darkest part of the shadow where direct sunlight is blocked. Because the Moon’s orbit is tilted about five degrees relative to Earth’s orbit, most full moons pass above or below the Earth’s shadow, preventing an eclipse.
During the event, the Moon does not disappear into darkness but takes on a subdued, colorful illumination. The Earth’s shadow is large enough to completely immerse the Moon, and the entire process of entering and exiting the shadow can last for several hours. The specific color and brightness during totality are determined by the interaction of light with Earth’s atmosphere.
The Physics Behind the Crimson Color
The reddish appearance of the Moon during totality is a consequence of Earth’s atmosphere acting as a prism and a filter. Even when the Moon is fully within the umbra, some sunlight manages to reach its surface indirectly by being bent, or refracted, around the edges of the planet.
The process that filters the sunlight is known as Rayleigh scattering. Short-wavelength light, such as blue and violet, is scattered most effectively by atmospheric molecules, which removes the blue light from the solar rays traveling toward the Moon.
Light with longer wavelengths, specifically red and orange, passes through the atmosphere with minimal scattering. This remaining long-wavelength light is then refracted into the cone of the Earth’s shadow, projecting the red light from all the world’s sunrises and sunsets onto the Moon’s surface.
The specific shade of red can vary significantly, depending on atmospheric conditions at the time of the eclipse. The presence of volcanic ash, dust, or pollution can block more light, leading to a darker, deeper red hue. A clear atmosphere, by contrast, may result in a brighter, more subtle coppery or orange color.
Tracing the Earliest Recorded Sightings
The earliest verified, datable record of a lunar eclipse points to the work of the ancient Babylonian civilization. Babylonian astronomer-scribes meticulously documented celestial events on clay tablets using cuneiform script.
This specific lunar eclipse occurred on March 19, 721 B.C. The Babylonians maintained systematic records of both solar and lunar eclipses from about 700 B.C. onward to aid in their astrological predictions and calendar keeping. Their ability to recognize and predict the cyclical nature of these events demonstrates a sophisticated level of astronomical knowledge.
Earlier records exist, though they are often less precise or disputed by modern scholars. A potential reference to a lunar eclipse is found in the ancient Chinese book Zhou-Shu, which may describe an event on January 29, 1137 B.C.
The difficulty with these ancient records lies in confirming whether observers noted the specific “blood” coloration or simply the darkening of the Moon. Nonetheless, the Babylonian documentation provides the earliest confirmed date of a total eclipse observation. Later Greek thinkers, such as Aristotle, used the circular shadow cast on the Moon during an eclipse as evidence that the Earth was a sphere.
Historical and Mythological Significance
Before the scientific explanation of orbital mechanics was understood, the sudden darkening and reddening of the Moon inspired widespread fear and mythological interpretations. Across many cultures, the “Blood Moon” was viewed as an omen of destruction, divine anger, or a battle in the heavens, necessitating rituals to protect communities.
The Mesopotamians, for example, believed a total lunar eclipse was a direct threat to the king. They developed a practice where the monarch would temporarily abdicate, and a proxy king would rule during the eclipse to absorb any ill fortune. Once the celestial event passed, the rightful ruler was reinstated, and the cosmic order was believed to be restored.
Inca Mythology
In the Inca Empire of South America, the red hue was interpreted as a sign that a mythical jaguar was attacking and devouring the Moon. To scare the celestial predator away and prevent it from turning its attention to Earth, people would make loud noises, shout, and encourage their dogs to bark and howl.
Norse Mythology
In Norse mythology, two giant wolves, Sköll and Hati, were said to perpetually chase the Sun and the Moon across the sky. An eclipse occurred when one of the wolves finally caught its prey, a sign that the end of the world, Ragnarök, was approaching.