How Many Stars Are in the Milky Way?
· 5 min read
cosmos galaxies
Our galaxy holds somewhere between 100 and 400 billion stars — but why can't astronomers give a single exact number? The answer reveals how galaxies are really measured.
The Short Answer
The Milky Way contains an estimated 100 to 400 billion stars. That enormous range might seem surprising for a question that sounds so simple, but counting the stars in our own galaxy is far harder than it appears — precisely because we live inside it.
Why We Can't Just Count Them
You might expect that counting stars is a matter of pointing a telescope and tallying up points of light. But the vast majority of the Milky Way's stars are too faint or too far away to see individually. Most stars are small, dim red dwarfs — far more common than bright Sun-like stars — and they're nearly invisible across galactic distances. On top of that, thick clouds of gas and dust block our view of large parts of the galaxy, especially toward the crowded galactic centre.
How Astronomers Estimate Instead
Rather than counting stars one by one, astronomers estimate the total by measuring the galaxy's mass. By observing how fast stars and gas orbit the galactic centre, they can calculate the Milky Way's total mass — roughly 1.5 trillion times the mass of the Sun, though most of that is invisible dark matter.
Subtracting the dark matter and gas leaves the mass held in stars. Dividing that by the average mass of a star gives the estimate. Because the "average star" is uncertain (there are far more tiny stars than giant ones), the final count lands in that broad 100-400 billion range.
Putting the Number in Perspective
If you tried to count 200 billion stars at a rate of one per second, it would take you more than 6,000 years. And the Milky Way is just one galaxy among an estimated two trillion in the observable universe. Multiply hundreds of billions of stars by trillions of galaxies, and the total number of stars in the observable universe reaches around 200 sextillion — a 2 followed by 23 zeros.
That's more stars than there are grains of sand on every beach and in every desert on Earth combined.