Why isn't there a solar eclipse every month?
The short answer
The Moon's orbit is tilted about 5 degrees compared with Earth's orbit around the Sun. Most months the new moon passes above or below the Sun from our viewpoint, so its shadow misses Earth entirely. An eclipse needs the new moon to arrive at one of the two points where the orbits cross.
If the orbits were flat, we would get twelve a year
Start with the world where the question would make sense. Imagine the Moon's orbit lying perfectly flat in the same plane as Earth's orbit around the Sun. Every new moon would then park exactly on the Sun-Earth line, drop its shadow on us, and produce an eclipse. Twelve or thirteen a year, as regular as a monthly bill. That is not the sky we live under, so something about the real orbit must be different.
Five degrees sounds like nothing and is enormous
The Moon's orbit is tilted roughly 5 degrees relative to Earth's. Tilt a phone by 5 degrees and nobody notices. Stretch that same angle across the 384,000 kilometres to the Moon and it becomes tens of thousands of kilometres of vertical offset. So at most new moons the Moon sits well above or well below the Sun as seen from Earth, and its shadow shoots harmlessly past the planet into empty space.
The two doorways are called nodes
A tilted orbit still has to cross the flat plane somewhere, and it does so at exactly two points. Astronomers call them nodes. Only at a node is the Moon at the right height for its shadow to reach us. So the rule for the whole subject is simple: new moon away from a node means no eclipse; new moon at a node means an eclipse. It is not chance, it is two conditions having to line up at once.
Eclipse seasons come twice a year and travel in pairs
The nodes only line up with the Sun during two windows each year, each around 35 days long. These are eclipse seasons. A window that long is wide enough to catch more than one alignment, which is why eclipses tend to arrive in pairs: a solar eclipse and a lunar eclipse roughly two weeks apart, as the Moon swings from one side of Earth to the other.
Even a direct hit is stingy
Across the whole planet there are typically four to seven eclipses a year counting both solar and lunar. But the strip of true totality is only around a hundred to a few hundred kilometres wide on a planet 40,000 kilometres around, and it falls somewhere different each time. The overall pattern repeats roughly every eighteen years, shifted about a third of the way around the globe, so the rerun belongs to someone else. Eclipses are not rare. They are choosy.
Sources
Full transcript: Why Eclipses Don't Happen Every Month
Why isn't there an eclipse every month? New moon happens every month. Eclipses don't. 12 times a year, sometimes 13, the moon slides around to the sun's side of the sky.
12 chances to block it, and this year only two of those new moons earned the black sun badge. The moon shows up to work every month, so why does the sky almost always skip the show? Today, the five degree answer. Welcome back to Watt & Why.
Six days ago, the sun went out over Iceland and Spain, and ever since, one question keeps landing in the comments: If the moon passes the sun every single month, why was that such a big deal? I promised you this one, let's solve it. First, let's build the world where the question would be right. Pretend the moon's orbit is perfectly flat—same table as the sun and the earth.
Nothing tipped, nothing tilted. Now run the year. Every new moon parks exactly on the sun-earth line. Shadow on Earth: blackout.
Next month: blackout. Next month: blackout. 12 for 12. An eclipse every month as regular as rent.
Sounds amazing, would honestly get old, and it is not the world you live in. So something about the real moon's orbit must be off. Here it is: the moon's orbit is tipped about 5° off the flat table. 5° sounds like nothing.
Tilt your phone 5°, nobody notices. But stretch that angle out to the moon's distance, and it becomes enormous. The moon can ride 35,000 km above the table or below it. So most months, at the exact moment of new moon, the shadow shoots past us, sailing over your head or under your feet and off into empty space.
Miss, miss, miss. That's a normal year in the shadow business. But a tipped hoop still has to cross the table somewhere, and it does—at exactly two points. Astronomers call them nodes.
Think of them as the only two doorways where the moon is actually at table height. Now, the rule of the whole episode: new moon away from a doorway, the shadow misses off the table, no show. But when a new moon lands right on a node—right phase, right crossing, both at once—that's an eclipse. Not luck, a key turning in a lock.
And here's the part almost nobody knows: those two doorways only line up with the sun twice a year. Two windows, each about 35 days long. Astronomers call them eclipse seasons, and a 35-day window is wide enough to catch more than one lineup. So eclipses travel in pairs: a sun eclipse and a moon eclipse about two weeks apart.
Check this year's receipts: February 17th, the sun; March 3rd, the moon. Then the summer window opened August 12th, the sun—you were there—and the pair's second half hasn't even happened yet. Next Friday night, the moon slides into Earth's shadow. You are inside an eclipse season right now.
One more reason eclipses feel so rare: even a perfect hit is stingy. The shadow's dark tip barely reaches Earth. It touches down as a strip just a couple hundred kilometers wide on a planet 40,000 km around. And each eclipse lands somewhere new.
The whole pattern roughly repeats every 18 years, but shifted a third of the way around the world. So the rerun is somebody else's show. Average wait for any one town to sit in totality: a few hundred years. That's why last Wednesday felt like winning the lottery—it kind of was.
So let me stamp the myth: eclipses are random luck. No, they're clockwork with a very picky filter. New moons aren't rare—12 or 13 a year, every year. Node hits are the bottleneck: 4 to 7 eclipses a year counting the whole planet, sun kind and moon kind.
Eclipses aren't rare, they're choosy. But one puzzle is still sitting on the table, and it's the strangest one of all: the moon is tiny, the sun is a monster, and yet last week you saw it, the moon covered the sun rim to rim like a lid made for the pot—not too small, not too big, exactly. No law of physics forces that fit, so why does it work? Saturday, the luckiest coincidence in the sky.
So remember, the moon's orbit is tipped 5°, so most shadows miss. A new moon on a node, that's an eclipse, and the doorways open twice a year in seasons, which is why eclipses travel in pairs. The sky isn't broken, it's on schedule, and your season isn't over. Thursday night, the moon slips into Earth's shadow and turns red.
Tuesday, I'll show you exactly how to watch it. You won't need glasses, just a window. But first Saturday, why the moon fits the sun so perfectly. See you on Watt & Why.
Transcript of the episode, lightly cleaned for readability.
Sample question
Question 1 of 10
Why is there not a solar eclipse at every new moon?
- The Moon's orbit is tilted, so its shadow usually misses Earth correct
- The Moon is too far away most months
- Clouds block the view
- The Sun moves out of alignment
Most months the Moon passes above or below the Sun as seen from Earth.
That is one of 10. The rest are not shown here, and the answer order changes every time you take the quiz.
Written by Watt & Why. Published 20 August 2026. Last reviewed 17 October 2026.