How Many Stars Are in the Milky Way?

NASA's answer is 100 to 400 billion — a range so wide it would be embarrassing if it were a measurement. It isn't one. Nobody has counted the stars, because most of them are too dim to see. The number is the galaxy's weight divided by a guess about the average star — and you can run that calculation yourself below.

Why nobody can just count them

Three numbers explain the whole problem. With the naked eye, under perfect dark skies, a human can see about 9,000 stars across the entire sky — roughly one star for every 30 million that exist. The European Space Agency's Gaia mission, the most ambitious star-mapping project ever attempted, has charted around 1.8 billion stars with exquisite precision — and that is still only about 1% of the galaxy. The other 99% are too faint, too far, or hidden behind the dust and glare of the galactic disc, especially on the far side of the centre, which we simply cannot see through.

So astronomers estimate instead. Measure how fast stars orbit, and gravity tells you the galaxy's mass. Subtract the gas, the dust and the dark matter, and you're left with the mass locked up in stars — somewhere around 40 to 90 billion times the Sun's mass, depending on the study. Then divide by the mass of a typical star. That last step is where the 4× spread comes from: if the average star is half a Sun, you get one answer; if the galaxy is stuffed with quarter-Sun red dwarfs, the count doubles. The estimator above is genuinely the same arithmetic the professionals use — just with their error bars turned into sliders.

Mostly red, mostly invisible

The reason the average-star guess matters so much is that the galaxy's population is nothing like the night sky suggests. The stars you can see by eye are a biased sample of show-offs — hot, bright, rare classes like Sirius and Vega. The actual census is dominated by stars you have never seen and never will.

This is also the answer to a question people specifically ask: how many stars like the Sun are out there? The Sun is a G-class star — technically a G2V yellow dwarf — and G-class stars make up roughly 7–8% of the galaxy. On a 200-billion-star estimate, that's in the neighbourhood of 15 billion broadly Sun-like stars. The Sun is not special by type; it's just the one we orbit.

The stars with names

Of the hundreds of billions of stars, only about 450 have official proper names, curated since 2016 by the International Astronomical Union's Working Group on Star Names. Everything else gets a catalogue number. And the names we do use carry a fingerprint of who did the astronomy: a striking share are Arabic — Betelgeuse, Aldebaran, Rigel, Deneb, Vega all descend from medieval Arabic star charts that preserved and extended Greek astronomy while Europe largely looked away.

None of them are standing still

Every one of those hundreds of billions of stars is in orbit around the galactic centre — and the supermassive black hole, Sagittarius A*, that sits there. The Sun is travelling at roughly 230 kilometres per second, about 26,000 light-years out from the middle, and still needs around 230 million years to complete one lap. That lap is called a galactic year. The Sun has finished only about 20 of them in its entire 4.6-billion-year existence; the last time we were on this side of the orbit with the dinosaurs just getting started.

Stars closer to the centre orbit faster; stars further out, slower — but not as much slower as visible matter alone predicts. That stubborn discrepancy in the galaxy's rotation curve, mapped by Vera Rubin in the 1970s, is the core evidence for dark matter, which outweighs all the stars combined by several times. Counting the stars, it turns out, only accounts for a minority of the galaxy.

The overdue supernova

With this many stars, statistics says the Milky Way should produce a supernova — the explosive death of a massive star — roughly once or twice a century. Yet no one has witnessed one in our galaxy since Kepler's supernova of 1604, observed five years before the telescope was even invented. We've gone over four centuries without a show we're "due" every fifty-odd years. (SN 1987A, the famous one, exploded in the Large Magellanic Cloud — a satellite galaxy, not ours.)

The explanation isn't that the explosions stopped — it's the dust again. A supernova around 1680 created the remnant Cassiopeia A, one of the brightest radio sources in the sky, and apparently almost nobody on Earth noticed the explosion itself because intervening dust dimmed it to near-invisibility. The galaxy has likely kept exploding on schedule, behind a curtain. Which is why astronomers keep such a close eye on Betelgeuse, the red supergiant in Orion about 550 light-years away: it will go supernova sometime in the next 100,000 years, and when it does it will outshine the full Moon for weeks — close enough, for once, that no dust can hide it, and far enough to be perfectly safe.

Eight questions about a galaxy

The 1604 question catches almost everyone.

The Milky Way holds somewhere between 100 and 400 billion stars — and the fact that we can only say "somewhere between" is, itself, the most honest fact on this page.