A person observes the captivating red glow of a blood moon during a total lunar eclipse. (Image credit: Dhruv Gajjar / EyeEm via Getty Images)
Have you ever witnessed the moon transform into a striking shade of red? This celestial event, often called a “blood moon,” is a truly awe-inspiring sight. While it might seem like a mystical occurrence, the science behind why the moon turns red is rooted in atmospheric phenomena and the mechanics of a lunar eclipse. Let’s delve into the fascinating reasons behind this crimson lunar display and when you can witness the next blood moon.
When Will the Next Blood Moon Grace Our Skies?
Mark your calendars, sky enthusiasts! The next total lunar eclipse, promising a spectacular blood moon, is anticipated to occur on March 13/14, 2025. Viewers across the entire United States will be perfectly positioned to witness the complete eclipse from beginning to end. Observers in parts of Europe, Asia, Australia, South America, the Pacific region, and Africa will also have the opportunity to experience at least a portion of this captivating celestial event.
Unpacking the Blood Moon Phenomenon
So, what exactly is a blood moon, and why does it take on this reddish hue? The term “blood moon” is essentially another name for a total lunar eclipse. This phenomenon occurs when the Earth positions itself directly between the sun and the moon, casting its shadow upon the lunar surface. While a blood moon doesn’t hold any unique astronomical significance beyond a standard lunar eclipse, its visual impact is undeniable. The typically bright, whitish moon undergoes a dramatic transformation, shifting to a mesmerizing red or ruddy brown.
Lunar eclipses are celestial events that are exclusively linked to the full moon phase. During a full moon, the sun fully illuminates the lunar surface as viewed from Earth. Most full moons pass without an eclipse because the moon’s orbit is slightly tilted relative to Earth’s and the sun’s orbital plane. However, at certain points, these orbital planes align. This alignment allows the Earth to move directly between the sun and the moon, intercepting the sunlight and causing a lunar eclipse.
Related Reading: Lunar eclipses 2025: When, where & how to see them
To further enrich your understanding and viewing experience, explore these related resources:
- How to photograph a lunar eclipse
- Using a teleconverter in lunar photography
- Moon viewing guide: What to look for on the lunar surface
If the Earth only partially obstructs the sun, and only the darkest part of its shadow (known as the umbra) falls on the moon, we witness a partial lunar eclipse. During this event, a dark shadow appears to take a visible “bite” out of the moon’s bright disk. Another type, a penumbral lunar eclipse, occurs when the moon passes through the Earth’s fainter, outer shadow (the penumbra). These eclipses are much subtler, often causing only a slight dimming of the moon, noticeable primarily to experienced sky watchers.
However, the true spectacle unfolds during a total lunar eclipse. In this case, the moon is completely immersed within the Earth’s umbral shadow. Intriguingly, even in total eclipse, the moon doesn’t disappear entirely. Instead, a faint amount of sunlight, refracted (bent) through Earth’s atmosphere, still reaches the lunar surface. This refracted light is key to understanding the red color.
A time-lapse sequence illustrating the progression of a total lunar eclipse, showcasing the moon’s journey into and out of Earth’s shadow, and the characteristic red glow at totality. (Image credit: Keith Burns/NASA/JPL)
The reason this refracted sunlight appears red is due to the same principle that causes sunsets and sunrises to be reddish. As sunlight passes through the Earth’s atmosphere, shorter wavelengths of light, like blue and violet, are scattered away more effectively – a phenomenon known as Rayleigh scattering. Longer wavelengths, such as red and orange, are less scattered and can pass through the atmosphere more readily. It’s this reddish component of sunlight, bent and filtered by Earth’s atmosphere, that illuminates the moon during a total lunar eclipse, giving it that distinctive “blood moon” appearance.
The precise shade of red a blood moon displays can vary depending on the conditions of Earth’s atmosphere at the time of the eclipse. Factors like the amount of dust, pollution, cloud cover, and volcanic aerosols present in the atmosphere can influence how much red light is refracted and scattered. For instance, a lunar eclipse occurring shortly after a significant volcanic eruption might result in a darker, deeper red hue due to increased atmospheric particles.
Our Earth holds a unique position in our solar system when it comes to lunar eclipses. Among all the planets and moons in our solar system, only Earth possesses a shadow that is just the right size to completely envelop the moon during a lunar eclipse. Interestingly, this celestial arrangement is not permanent. The moon is gradually drifting away from Earth at a rate of about 1.6 inches (4 centimeters) per year. While this recession is slow, over vast stretches of astronomical time, the Earth’s shadow will eventually become too small to fully cover the moon. For now, we are fortunate to experience approximately two to four lunar eclipses every year, with each eclipse being visible from roughly half of the Earth’s surface.
A Blood Moon’s Historical Impact: Christopher Columbus’s Ingenious Use
In ancient times, before the scientific understanding of lunar eclipses, the sudden transformation of the moon into a blood-red orb often evoked fear and superstition in various cultures. However, at least one historical figure, the explorer Christopher Columbus, turned a blood moon to his advantage in 1504.
Historical accounts, notably documented by Space.com Skywatching columnist Joe Rao, recount how Columbus and his crew found themselves stranded on the island we now know as Jamaica. Initially, the indigenous Arawak people extended hospitality, but as time passed, tensions escalated. Columbus’s crew became unruly, resorting to theft and violence against the natives. Consequently, the Arawak became reluctant to provide food, and Columbus faced the looming threat of famine.
A captivating blood moon rises above the California landscape in 2018, showcasing the dramatic red coloration during a total lunar eclipse. (Image credit: Getty Images)
Fortuitously, Columbus possessed an almanac that predicted an upcoming lunar eclipse. Seizing this opportunity, he devised a plan. He warned the Arawak people that the Christian God was displeased with their withholding of provisions for him and his men. As a sign of divine anger, Columbus declared, God would turn the moon blood-red. When the predicted lunar eclipse unfolded exactly as foretold, fear gripped the Arawak. According to the account of Columbus’s son Ferdinand, the terrified people, with “great howling and lamentation,” rushed to the ships laden with food, pleading with Columbus to intercede with his God on their behalf. Thus, a blood moon, understood through the lens of fear and divine omen, became the unlikely instrument that saved Columbus and his crew from starvation.
Further Resources for Eclipse Enthusiasts
For those eager to delve deeper into the world of eclipses, especially budding astronomers, consider exploring these resources: Solar and Lunar Eclipses (Explore Outer Space) by Ruth Owen. NASA’s Space Place webpage also offers engaging information about various lunar phenomena.
Bibliography
K. G. Strassmeier et al “High-resolution spectroscopy and spectropolarimetry of the total lunar eclipse January 2019,” Astronomy & Astrophysics, Volume 653, March 2020, https://doi.org/10.1051/0004-6361/201936091
Natural History Museum, “Lunar eclipse guide: what they are, when to see them and where,” May 27, 2021.
Royal Museums Greenwich, “How to see a lunar eclipse,” January, 2022.
Jessica Marshallsay, “Blood moon rising: How lunar eclipses might help us find life on other planets,” The University of Queensland, January, 2022.
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Scott Dutfield
Contributor
Scott Dutfield is a staff writer for How It Works magazine and a contributor to various science and space publications including BBC Wildlife magazine, World of Animals magazine, Space.com, and All About History magazine. He holds a master’s degree in science and environmental journalism and a bachelor’s degree in conservation biology from the University of Lincoln in the U.K. His diverse experience includes participation in animal conservation projects ranging from English bird surveys to wolf monitoring in Germany and leopard tracking in South Africa.
