Total lunar eclipses, popularly called blood moons, occur on average a little more than once per year, and humanity has witnessed well over a hundred in recorded history alone. In the 21st century through early 2025, more than two dozen total lunar eclipses have already taken place. The exact count depends on how far back you look and whether you restrict the term “blood moon” to total eclipses or include some deeper partial ones, but the number is far larger than the handful most people can recall. The reason so few stick in memory has less to do with rarity and more to do with visibility from any single location and the relatively recent explosion of the term “blood moon” itself.
What Counts as a Blood Moon
Astronomers distinguish three types of lunar eclipse. A penumbral eclipse, where the Moon passes through Earth’s faint outer shadow, is so subtle most people wouldn’t notice it without being told. A partial eclipse sends part of the Moon into the dark inner shadow (the umbra), producing an obvious bite of darkness but not the dramatic all-over red glow. A total lunar eclipse, where the entire Moon sits inside the umbra, is what earns the “blood moon” label. During totality, the Moon doesn’t go black. Instead, sunlight bent through Earth’s atmosphere reaches the lunar surface, and because shorter wavelengths of light are scattered away by the atmosphere, what remains is dominated by deep reds and oranges.
When people ask “how many blood moons have we had,” they almost always mean total lunar eclipses. Partial and penumbral events don’t produce the vivid red that made the phrase famous. That said, even among total eclipses, the color varies enormously from one event to the next, a point worth returning to below.
Blood Moons in Recent Memory
Since the year 2000, the 21st century has produced a steady stream of total lunar eclipses. Some of the ones most widely observed include the pair in 2003 and the pair in 2004, the widely watched trio in 2007 and 2008, and the heavily publicized sequence in 2014 and 2015. More recently, January 2018 brought a total eclipse that coincided with a “supermoon” (when the Moon is near its closest orbital point to Earth), attracting huge public interest. July 2018 delivered the longest totality of the century up to that point, lasting about 103 minutes, though it was visible mainly from the Eastern Hemisphere. January 2019, May 2021, May 2022, November 2022, and March 2025 round out the list of recent events.
Not every one of these was visible from every continent. A total lunar eclipse can only be seen from the half of Earth facing the Moon during the event, so any single observer misses roughly half of all blood moons simply because of geography and timing. That’s a big reason the events feel rarer than they actually are. Someone living in North America, for instance, had excellent views of the 2014, 2015, 2018, 2019, and 2022 eclipses but missed the July 2018 and May 2021 events almost entirely.
Why the Moon Turns Red
The color comes from the same physics that makes sunsets red. Earth’s atmosphere bends sunlight around the planet’s edge and into the shadow cone. As that light passes through the lower atmosphere, shorter wavelengths (blues and greens) are scattered away by air molecules far more efficiently than longer wavelengths. What survives the journey is heavily skewed toward the red end of the spectrum.
Modeling work using satellite atmospheric data has confirmed that the central portions of Earth’s umbral shadow appear deep red during almost all eclipses because of this preferential removal of short wavelengths in the lower troposphere.1Applied Optics. Simulating irradiance and color during lunar eclipses using satellite data The result is a Moon bathed in the combined light of every sunrise and every sunset happening on Earth at that moment, projected onto the lunar surface all at once. It’s a genuinely poetic image once you picture it from the right angle: an astronaut standing on the Moon during a total eclipse would see Earth ringed by a thin band of glowing red and orange light.
Why Some Blood Moons Are Darker Than Others
Not all blood moons look the same. Some glow a bright copper-orange, while others turn such a dark brownish-red that the Moon nearly vanishes. The main variable is what’s floating in Earth’s atmosphere at the time, particularly volcanic aerosols in the stratosphere.
When a major volcanic eruption lofts sulfur-rich particles into the upper atmosphere, those particles block and scatter even the longer wavelengths that normally make it through. A study comparing 21 total lunar eclipses between 1960 and 1982 found that stratospheric aerosol loads from volcanic eruptions profoundly affected the brightness of the eclipsed Moon, and researchers used those brightness variations to estimate global aerosol levels.2PubMed. Volcanic aerosols and lunar eclipses The December 1992 eclipse, which followed the massive 1991 eruption of Mount Pinatubo in the Philippines, was so dark that parts of the Moon were essentially invisible to the naked eye.
Astronomers have used the Danjon scale to categorize the appearance of eclipsed Moons for over a century. It runs from L0 (very dark, Moon almost invisible, brownish) through L4 (very bright, copper-red or orange, with a bluish-white rim). An eclipse’s Danjon rating is shaped by how much dust and aerosol sits in Earth’s stratosphere at the time, how deeply the Moon passes through the umbra, and even regional weather patterns along Earth’s limb. Two observers watching the same eclipse from different locations can honestly assign different Danjon values, because the slice of atmosphere bending light toward the Moon is slightly different depending on the observer’s perspective.
How the Term “Blood Moon” Took Over
For most of the history of astronomy, total lunar eclipses were just called total lunar eclipses. The phrase “blood moon” has roots in religious scripture. References to the Moon “turning to blood” appear in multiple biblical passages, and similar imagery exists in Islamic eschatology and other traditions. A cultural study examining the intersection of astronomy and religion across multiple civilizations found that red moons are associated with eschatological or prophetic signs in Christianity, Islam, Ethiopian, Egyptian, and Jewish traditions.3Lakhomi Journal : Scientific Journal of Culture. The Red Moon and Beyond: Astronomical Events in the Context of Global Faith and Culture
The term exploded into mainstream use in 2013 and 2014, largely because of a specific astronomical coincidence called a tetrad. A tetrad is a sequence of four consecutive total lunar eclipses with no partial eclipses in between, spaced roughly six months apart. The 2014–2015 tetrad (April 2014, October 2014, April 2015, September 2015) happened to coincide with Jewish holidays, and several popular books and media figures framed the alignment as prophetically significant. Whether you found the framing compelling or eye-roll-inducing, it succeeded spectacularly at embedding “blood moon” into everyday language. Before 2013, Google search trends for the term barely registered. Afterward, every total lunar eclipse was a “blood moon” in headlines worldwide.
Tetrads themselves aren’t especially rare, but they don’t happen every decade either. There were none between 1600 and 1900, then eight in the 20th century. The 21st century is expected to see another eight or so. The clustering is a result of how the geometry of the Moon’s orbit slowly shifts over centuries, sometimes producing stretches where total eclipses line up neatly and other times leaving long gaps.
The Historical Record Going Back Millennia
People have been watching and recording lunar eclipses for a very long time. Ancient Babylonian clay tablets contain systematic records of eclipses stretching back roughly 2,700 years. A major analysis of ancient and medieval eclipse records compiled observations spanning from 720 BC to AD 1600, using them alongside more modern data to study changes in Earth’s rotation rate over time.4PubMed Central. Measurement of the Earth’s rotation: 720 BC to AD 2015 Those records are valuable precisely because eclipses are such sharply timed events. If an ancient chronicle says a total lunar eclipse was visible from a specific city on a specific night, modern astronomers can check that against calculated eclipse paths and figure out whether Earth’s rotation has sped up or slowed down since then.
The sheer number of lunar eclipses over that span is staggering. In any given century, you can expect somewhere around 150 to 160 lunar eclipses of all types, of which roughly 55 to 70 will be total. Stretch that back across the nearly three millennia of recorded observations and you’re looking at well over a thousand documented total lunar eclipses. Extend the calculation across the five millennia that modern astronomical models can reconstruct with high accuracy and the total count of blood moons reaches into the thousands. Of course, many of those occurred before anyone was keeping records, and many that were recorded have been lost. The surviving written record captures only a fraction of what actually happened in the sky.
Why You Can’t See Every Blood Moon
A total lunar eclipse lasts, from first contact with the umbra to last contact, somewhere between about one and nearly four hours, with the totality phase itself ranging from a few minutes to around 106 minutes at the theoretical maximum. Unlike solar eclipses, which require you to be standing in a narrow ground track, a lunar eclipse is visible from anywhere on the night side of Earth. That sounds generous, and it is, relative to solar eclipses. But it still means roughly half the planet misses each event.
This geographic filter is why personal experience of blood moons is so variable. Someone in their forties living in North America has probably had the opportunity to see around 10 to 15 total lunar eclipses in their lifetime, assuming clear skies. Someone in Southeast Asia would have seen a somewhat different set. The Moon doesn’t care about time zones, but the Sun does, and if it’s daytime where you live when the eclipse happens, you’re out of luck.
Weather compounds the issue. Cloud cover has spoiled more eclipse-viewing plans than any other factor. A dedicated eclipse chaser who travels to favorable locations and checks weather forecasts obsessively might see the majority of total lunar eclipses in their adult lifetime. A casual skywatcher who only steps outside when reminded by a news alert will catch far fewer.
What Blood Moons Reveal About Earth’s Atmosphere
Beyond their visual spectacle, blood moons have become unexpectedly useful scientific tools. When sunlight passes through Earth’s atmosphere on its way to the eclipsed Moon, it carries an imprint of whatever it encountered along the way, including oxygen, water vapor, ozone, and aerosols. By studying the spectrum of light reflected off the eclipsed lunar surface, researchers can essentially read Earth’s atmospheric fingerprint.
Spectroscopic observations during total eclipses have detected clear absorption signatures from atmospheric molecules. Polarization measurements of light from the Moon’s umbral shadow have revealed features near 760 nanometers corresponding to molecular oxygen absorption (the so-called A band) and additional features in the 560–580 nanometer range tied to oxygen collision complexes.5The Astronomical Journal. Polarized Transmission Spectrum of Earth as Observed during a Lunar Eclipse These are the same kinds of spectral fingerprints that astronomers hope to detect in the atmospheres of distant exoplanets when starlight filters through them during transits.
In fact, lunar eclipses serve as a test bed for exactly that kind of exoplanet research. During a blood moon, Earth is effectively “transiting” the Sun from the Moon’s perspective. Researchers have used this geometry to validate the techniques they plan to deploy with space telescopes aimed at Earth-sized planets around other stars, checking whether retrieval methods can correctly identify gases like water vapor, carbon dioxide, and ozone in Earth’s known atmosphere by analyzing the eclipse-filtered light.6The American Astronomical Society / IOP Publishing. Earth as a Transiting Exoplanet: A Validation of Transmission Spectroscopy and Atmospheric Retrieval Methodologies for Terrestrial Exoplanets If the method works on Earth’s atmosphere observed via the Moon, there’s reason to trust it on a rocky planet orbiting a distant star.
Blood moons have also been observed at microwave wavelengths from orbiting weather satellites. Measurements during a total eclipse at frequencies between 89 and 183 gigahertz tracked how the Moon’s brightness temperature dropped as it entered Earth’s shadow, establishing a relationship between frequency and temperature drop that helps calibrate microwave instruments used in weather forecasting and climate monitoring.7The Planetary Science Journal. Observation of a Lunar Eclipse at 89, 150, and 183 GHz The Moon, it turns out, serves as a reliable calibration target for satellite sensors, and eclipses provide a controlled scenario to test that reliability.
Upcoming Blood Moons
For anyone keeping a calendar, September 2025 brings a total lunar eclipse visible primarily from the Pacific, Asia, Australia, and eastern Africa. After that, March 2026 offers a total eclipse favoring the Americas, Europe, and Africa. The next few years following those include additional total eclipses in 2028 and 2029, so the 2020s will ultimately be a reasonably productive decade for blood moon watchers regardless of where they live.
If you want to see one, the practical advice is simple. Check the date and timing for your specific location well in advance. Find a spot with a clear view of the sky in the direction the Moon will be. Give yourself at least 30 minutes before totality to let your eyes adjust and watch the partial phases build. And have a backup plan for clouds, because the atmosphere that makes the Moon turn red is the same one that can block your view entirely. No special equipment is needed. Unlike a solar eclipse, a lunar eclipse is perfectly safe to watch with the naked eye, and binoculars or a small telescope will bring out the color gradations across the lunar surface during totality in a way that photographs rarely capture.