How many stars are there in the universe?
The standard figure is 2 × 10^23 — 200 billion trillion, or a 2 followed by 23 zeros — and it is uncertain by at least a factor of ten either way. It applies to the observable universe, the sphere of about 93 billion light years across from which light has had time to reach us; the universe as a whole may be far larger or infinite, in which case the honest answer to the question is that there is no answer. The number is a product of two badly-known factors, so its uncertainty is the product of theirs.
How the figure is arrived at
Multiply the number of galaxies by the average number of stars per galaxy. Both are estimated from deep-field images: point a telescope at an apparently empty patch of sky for days, count what appears, and scale by the number of such patches in the whole sky. Dwarf galaxies are the problem — they are far more numerous than large spirals and far harder to see, so they dominate the count of galaxies and contribute little to the count of stars.
How confident it is
- Low estimate
- 10,000,000,000,000,000,000,000
- High estimate
- 1,000,000,000,000,000,000,000,000
- Spread
- 100.0× between the bounds
Other space and the universe counts
- How many stars are there in the Milky Way? between 100 billion and 400 billion
- 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 universe?
- about 200 billion trillion
- How is that estimated?
- Multiply the number of galaxies by the average number of stars per galaxy. Both are estimated from deep-field images: point a telescope at an apparently empty patch of sky for days, count what appears, and scale by the number of such patches in the whole sky. Dwarf galaxies are the problem — they are far more numerous than large spirals and far harder to see, so they dominate the count of galaxies and contribute little to the count of stars.
Related pages
- How many stars are there in the Milky Way? between 100 billion and 400 billion
- 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))