You're standing outside in the shivering cold, staring up at a moon that looks like it’s been dipped in rust or maybe old wine. It’s eerie. It's beautiful. Most people call it a "Blood Moon," though if you ask a NASA scientist, they’ll probably push up their glasses and tell you it’s actually a total lunar eclipse. But whatever you call it, the big question is always the same: how often do blood moons occur, and why does it feel like we miss them every time they show up?
The answer isn't a simple "once a year" or "every decade." It’s messy. Orbital mechanics are kind of chaotic, or at least they feel that way to us down here on Earth.
The Math Behind the Red
A Blood Moon happens when the Earth slides perfectly between the sun and the moon. Our planet casts a shadow. But because we have an atmosphere filled with nitrogen and oxygen, the sunlight doesn't just stop. It bends. This is called Rayleigh scattering. It’s the same reason the sky is blue and sunsets are red. The shorter blue wavelengths of light get scattered away, while the longer red wavelengths pass through, bend around the curve of the Earth, and hit the lunar surface.
Basically, a Blood Moon is the light of every single sunrise and sunset on Earth hitting the moon all at once. Pretty poetic for a rock in space, right?
But the timing is tricky. The moon’s orbit around Earth is tilted by about 5 degrees relative to Earth’s orbit around the sun. If they were perfectly aligned, we’d have a Blood Moon every single month. Instead, most months, the moon passes slightly above or below the Earth's shadow. It misses the target. To get that deep crimson hue, the alignment has to be precise.
So, How Often Do Blood Moons Occur?
On average, you're looking at about two lunar eclipses a year. But hold on—not all of those are "Blood Moons." Some are "penumbral" eclipses where the moon just looks a bit dusty or dim. Others are partial eclipses where it looks like something took a bite out of a cookie.
The real deal—the Total Lunar Eclipse—happens roughly once every 1.5 years.
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- Some years have zero total eclipses.
- Other years might have two back-to-back.
- Occasionally, we get a "Tetrad."
A Tetrad is a series of four consecutive total lunar eclipses with six full moons in between each one. This is rare. Well, relatively. In the 21st century, we actually have quite a few (eight, to be exact). But in some centuries, like the 17th, 18th, and 19th, there were exactly zero Tetrads. If you lived in the year 1850, you might have gone your whole life without seeing that specific pattern.
Why Location Is Everything
Here is the annoying part. Even if a Blood Moon is happening, you might not see it. Unlike a solar eclipse, which traces a tiny path across a few states or countries, a lunar eclipse is visible to anyone on the night side of the planet. If the moon is above your horizon while it’s in the Earth’s shadow, you’re in luck.
But if the eclipse happens at 2:00 PM your time? You’re seeing nothing but blue sky.
Fred Espenak, a retired NASA astrophysicist known as "Mr. Eclipse," has calculated these paths for decades. His data shows that while the events aren't "rare" in a global sense, they are rare for you. On average, a specific spot on Earth will see a total lunar eclipse about once every 2.5 years. But clouds? Clouds are the enemy. You could have a perfect eclipse scheduled, but one stubborn overcast night in Seattle or London means you're waiting another few years for the next shot.
The "Super Blue Blood Moon" Hype
Every few years, the internet loses its mind over a "Super Blue Blood Moon." This sounds like something out of a fantasy novel, but it’s just a coincidence of three independent cycles.
- Super: The moon is at perigee (its closest point to Earth), making it look 14% bigger.
- Blue: The second full moon in a single calendar month.
- Blood: The total eclipse is happening.
Does it look different? Honestly, not really. The "Super" part is hard to see with the naked eye unless you're a seasoned observer. The "Blue" part has nothing to do with color. But the "Blood" part? That’s the showstopper.
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What the Color Tells Us About Earth
The "Blood" isn't always the same shade. Sometimes it's a bright, fiery orange. Other times, it’s so dark it’s almost invisible, like a charcoal smudge in the sky. This is measured by the Danjon Scale, ranging from 0 (nearly invisible) to 4 (copper-red or orange).
Interestingly, the color of the Blood Moon is a direct report card of Earth’s atmosphere. If there has been a massive volcanic eruption recently—think Mount Pinatubo in 1991—the stratosphere is filled with ash and aerosols. These particles block the light even more, leading to a much darker, gloomier Blood Moon. If the air is clean, the red is more vibrant.
Historical Fear and Modern Wonder
Before we knew about Rayleigh scattering, people were terrified. The Inca thought a jaguar was attacking the moon and would eventually come down to eat people. They’d make their dogs bark and howl to scare the jaguar away. In ancient China, it was a celestial dragon.
Today, we just take photos with our iPhones (which usually come out looking like a blurry orange dot). But there’s still something primal about it. Seeing the moon—the most constant thing in our lives—change color feels significant.
When Is the Next One?
If you’re wondering when to set your alarm, you need to look at the upcoming windows. We recently had a dry spell, but the late 2020s are looking decent.
- March 14, 2025: A total lunar eclipse will be visible from the Americas, Europe, and Africa.
- September 7, 2025: This one favors Europe, Africa, Asia, and Australia.
- March 3, 2026: A great opportunity for those in the Pacific and North America.
How to Actually Watch One
You don't need fancy equipment. This isn't a solar eclipse; you won't go blind if you look at it.
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First, get away from city lights if you can. While you can see a Blood Moon from a skyscraper in NYC, the stars that pop out during totality are half the fun. When the moon goes dark, the surrounding stars suddenly look much brighter because the "light pollution" from the full moon is gone.
Second, use binoculars. Even a cheap pair of $20 binoculars will let you see the crater detail through the red shadow. It’s breathtaking.
Third, be patient. A total lunar eclipse takes hours. The "totality" phase—where the moon is fully red—usually lasts between 30 and 100 minutes. Pack a thermos of coffee.
Why the Timing Matters for Science
NASA doesn't just watch these for the vibes. During an eclipse, the moon’s surface temperature drops off a cliff. It goes from boiling to deep-freeze in a matter of hours. By watching how fast the surface cools using thermal cameras, scientists can figure out what the lunar soil (regolith) is made of. Rocks stay warm longer than fine dust.
So, while you're standing there wondering how often do blood moons occur, scientists are using that exact frequency to map the geology of another world.
Actionable Next Steps for Stargazers
- Check your local visibility: Don't just Google "when is the next Blood Moon." Go to a site like Time and Date and put in your specific city. It will tell you the exact minute the shadow starts.
- Download a Sky Map app: Apps like Stellarium or SkySafari will help you identify the constellations that appear when the moon dims.
- Prepare your camera gear: if you’re using a DSLR, you’ll need a tripod. Long exposures are mandatory because the moon gets much darker than you expect.
- Join a local astronomy club: Many libraries and universities set up telescopes for the public during total eclipses. It’s a great way to see the event through a professional lens for free.
The next time the moon turns that haunting shade of red, you'll know it's just our atmosphere doing a lens trick, but that doesn't make it any less magical. Mark your calendar for 2025 and 2026. The shadows are already moving.