How many stars are there in the Milky Way?
The usual quoted range is 100 to 400 billion, and the spread is not laziness — it reflects a real disagreement about how much of the Galaxy's mass is in small, faint stars. Most stars are red dwarfs far too dim to see individually at galactic distances, so they are inferred rather than counted. The Gaia mission has measured precise positions and distances for about 1.8 billion stars, which sounds enormous and is roughly 1% of the Galaxy.
How the figure is arrived at
Two routes that have to be reconciled. Measure the Galaxy's rotation curve to get its total mass, subtract the dark matter and gas, and divide the stellar remainder by an average stellar mass of roughly 0.2 to 0.5 solar masses. Or count the stars you can actually see in a well-surveyed patch of sky and scale up using a model of the Galaxy's shape. The two methods agree only to within a factor of three, which is where the quoted range comes from.
How confident it is
- Low estimate
- 100,000,000,000
- High estimate
- 400,000,000,000
- Spread
- 4.0× between the bounds
Other space and the universe counts
- How many stars are there in the universe? about 200 billion trillion
- How many atoms are there in the universe? about 10^80
- How many galaxies are there? hundreds of billions — possibly 2 trillion
- How many satellites are in orbit? about 12,000 active satellites
- How many moons are there in the solar system? about 900 confirmed, and the number keeps moving
- How many planets are there in the galaxy? at least 100 billion — probably more planets than stars
- How many stars can you see with the naked eye? about 9,000 over the whole sky; roughly 2,500 at once
- How many constellations are there? exactly 88
- How much space junk is there? about 40,000 tracked objects, and over 130 million fragments too small to track
- How many asteroids are there? about 1.4 million catalogued
Common questions
- How many stars are there in the Milky Way?
- between 100 billion and 400 billion
- How is that estimated?
- Two routes that have to be reconciled. Measure the Galaxy's rotation curve to get its total mass, subtract the dark matter and gas, and divide the stellar remainder by an average stellar mass of roughly 0.2 to 0.5 solar masses. Or count the stars you can actually see in a well-surveyed patch of sky and scale up using a model of the Galaxy's shape. The two methods agree only to within a factor of three, which is where the quoted range comes from.
Related pages
- How many stars are there in the universe? about 200 billion trillion
- How many atoms are there in the universe? about 10^80
- How many galaxies are there? hundreds of billions — possibly 2 trillion
- How many satellites are in orbit? about 12,000 active satellites
- How many moons are there in the solar system? about 900 confirmed, and the number keeps moving
- How many planets are there in the galaxy? at least 100 billion — probably more planets than stars
- How many stars can you see with the naked eye? about 9,000 over the whole sky; roughly 2,500 at once
- How many constellations are there? exactly 88
- How many people are there in the world? Living things and the natural world
- How many countries are there in the world? Things people built
- How many bones are in the human body? The human body
- How many grains of sand are there on Earth? Living things and the natural world
- How many ants are there in the world? Living things and the natural world
- How many trees are there in the world? Living things and the natural world
Sources
- NASA — National Aeronautics and Space Administration (Public domain (US Government))