Here's a number that should stop you cold: there are somewhere between 100 and 400 billion stars in the Milky Way.
Not hundreds. Not thousands. Hundreds of billions.
How do you even begin to count something like that?
The short answer: you don't. You estimate — and the method is a masterclass in Fermi-style thinking.
You Can't Count Them All
Counting every star in the Milky Way, one by one, would take around 1,900 years working without any breaks. And that's assuming you could see them all, which you can't — dust, gas, and the sheer scale of the galaxy block most stars from view entirely.
So astronomers use two smarter approaches.
Method 1: Weigh the Galaxy
One method is to estimate the total number of stars by taking the mass of the galaxy, then figuring out how many stars are required to give the galaxy that mass.
Astronomers calculate the Milky Way's total mass by studying how fast stars and gas clouds orbit the galactic centre. The faster things orbit at a given distance, the more mass must be pulling them. From that, they derive the galaxy's total stellar mass — and divide by the average mass of a star.
The catch? Not all stars are the same size. The assumed average mass matters a lot, which is why estimates vary so widely.
Method 2: Sample a Patch of Sky
Another method is to accurately count the number of stars in a small patch of sky, then extrapolate — assuming that patch is representative of the entire galaxy.
The ESA's Gaia spacecraft, which has been mapping the sky since 2013, has catalogued the positions of 1.7 billion stars in the Sun's neighbourhood up to a distance of 326 light-years. Astronomers then model the rest of the galaxy from that sample.
The problem is that the faintest, smallest stars — red dwarfs — are hard to detect even for Gaia, and they make up the majority of stars in the galaxy. Miss them in your sample, and your final number is too low.
The Answer (Such As It Is)
The most common estimate is between 100 billion and 400 billion stars — and that wide range isn't scientific sloppiness. It's honest uncertainty in the face of a genuinely hard problem.
What's remarkable isn't that scientists disagree on the precise number. It's that they can arrive at a number that's correct to within a factor of a few, for a galaxy 100,000 light-years across, without ever leaving our solar system.
That's estimation at a cosmic scale — which is exactly what Magnitudle trains you for.