How Many
Stars Are
in the Universe?
Calculating the total stellar population requires combining deep-field imaging and gravitational mass modelling across 2 trillion galaxies. The answer challenges the human capacity for scale β reaching into the hundreds of sextillions.
How Many Stars Are There?
π Drag the slider to zoom from Earth's sky to the edge of the observable universe
How Many Stars
Are in the Universe?
Astronomers estimate the observable universe holds around 200 sextillion stars. Here is the complete guide to how that number was calculated, what it means, and why it keeps changing.
The Number: 200 Sextillion
The most widely cited estimate for the number of stars in the observable universe is approximately 200 sextillion β written out, that is 200,000,000,000,000,000,000,000, or 2 Γ 10Β²Β³. It is a number so far beyond human intuition that every attempt to comprehend it requires analogy.
To be precise: this is not a count. No one has counted 200 sextillion stars. Instead, astronomers have used a combination of deep-field imaging, gravitational mass estimation, stellar population modelling, and statistical extrapolation to arrive at a figure they are confident is accurate to within a factor of a few. The current best estimate sits between 10Β²Β² and 10Β²β΄, with 2 Γ 10Β²Β³ as the central value.
This figure applies only to the observable universe β the sphere of space from which light has had enough time to reach us in the 13.8 billion years since the Big Bang. The full universe, which almost certainly extends far beyond what we can see, likely contains an incomprehensibly larger number of stars. Some cosmological models suggest the full universe could be 10Β²Β³ times larger than the observable portion.
"There are more stars in the observable universe than there are grains of sand on all of Earth's beaches β by a factor of roughly ten thousand."
β Carl Sagan, Cosmos: A Personal Voyage (1980)The Sand Grain Benchmark
The most famous scale comparison in astronomy is the "sand on Earth" benchmark. Howard C. McAllister at the University of Hawaii estimated that the total number of sand grains on Earth's beaches and deserts is approximately 7.5 Γ 10ΒΉβΈ β or 7.5 quintillion. That sounds impossibly large.
The estimated star count of 2 Γ 10Β²Β³ is roughly 10,000 times larger than the Earth's total sand grain count. In other words, for every single grain of sand on every beach, desert, riverbed, and ocean floor on our planet, there are approximately ten thousand stars burning somewhere in the observable universe.
Grains of Sand on Earth
Stars in the Universe
There are approximately 10,000 stars for every single grain of sand on Earth β including every beach, desert, riverbed and ocean floor on the planet.
If that still feels abstract, consider this secondary comparison: the number of stars exceeds the number of cells in all human bodies on Earth combined (estimated at ~3.7 Γ 10Β²β° per person Γ 8 billion people β 3 Γ 10Β³β° cells in total β which is actually larger still, but of a comparable cosmic magnitude). The universe contains roughly as many stars as there are cups of water in all of Earth's oceans.
How Astronomers Count Stars
Counting stars is one of astronomy's oldest and most challenging problems. The methodology has evolved dramatically over 400 years, from squinting through early telescopes to analysing petabytes of spectroscopic data from orbital observatories. Today, astronomers use three primary approaches β and none of them involve literally counting individual stars in the universe.
Astronomers observe a galaxy, measure its luminosity profile, estimate its stellar mass using known mass-to-light ratios for different stellar populations, then divide by the average stellar mass to get a star count. This method is precise for nearby galaxies but becomes uncertain at cosmological distances.
The Hubble and Webb telescopes photograph tiny patches of sky, count the galaxies visible, then extrapolate to the full observable sphere. Multiply by the average star count per galaxy and you get the universal total. This is the method behind the 2-trillion-galaxy estimate published in 2016.
By measuring the total intensity of all light across the sky at different wavelengths β a technique called Extragalactic Background Light (EBL) measurement β astronomers can work backwards to estimate the total number of stellar sources. This acts as an independent cross-check on the other two methods.
Crucially, all three approaches arrive at compatible answers: somewhere between 10Β²Β² and 10Β²β΄ stars. The convergence of independent methodologies gives astronomers confidence that the estimate, while not precise, is in the correct order of magnitude.
The 4 Pillars of Universal Calculation
Within those broader approaches, four specific observational and analytical techniques do the heavy lifting. Each addresses a different part of the problem β together, they triangulate the final number.
The Hubble Ultra Deep Field (2004) and Hubble eXtreme Deep Field (2012) photographed a region of sky just 2.4 arcminutes wide β about one thirteen-millionth of the total sky β and found roughly 5,500 galaxies. Webb's CEERS survey found galaxies at even higher redshifts. Scaling these counts to the full sky gives the total galaxy population.
The rotational velocity of a galaxy β measured by Doppler shifts in spectral lines β reveals its total gravitational mass. After subtracting contributions from dark matter and gas, astronomers calculate the stellar mass and convert it to a star count using stellar initial mass functions (IMF).
Not all galaxies have the same stellar makeup. Elliptical galaxies tend to have older, redder stars; spiral galaxies host active star formation. Astronomers use spectral energy distribution (SED) fitting to model the stellar populations of distant galaxies and refine per-galaxy star counts.
The observable universe is bounded by the particle horizon β approximately 46.5 billion light-years in every direction (the universe has expanded since the most distant light was emitted). Stars beyond this boundary cannot be counted because their light has not reached us, and never will in a finite-age cosmos.
The Galactic Multiplier
The simplest and most intuitive route to the 200-sextillion figure is the sampling and extrapolation method. It breaks the problem into two manageable sub-questions: how many galaxies are there, and how many stars does an average galaxy contain?
A 2 followed by 23 zeros. This covers only stars within the 46.5 billion light-year observable radius.
The 2-trillion galaxy figure comes from a landmark 2016 study by Christopher Conselice and colleagues at the University of Nottingham, published in The Astrophysical Journal. Using data from the Hubble Space Telescope combined with mathematical modelling of galaxies too faint to directly observe, they concluded the observable universe contains at least ten times more galaxies than previously thought β revising the estimate up from ~200 billion to over 2 trillion.
The 100-billion star average per galaxy is itself a weighted mean. The Milky Way contains an estimated 100β400 billion stars. Dwarf galaxies may contain only a few million. Giant ellipticals like IC 1101 may hold over 100 trillion stars. When averaged across the full distribution of galaxy types and sizes, 100 billion is a conservative and well-supported central estimate.
Scale Comparisons: From Your Backyard to the Cosmos
One of the best ways to feel the scale of the star count is to zoom out in stages β from what the naked eye can see on a clear night to the full observable universe.
| Scale | Example | Approx. Star Count | Notes |
|---|---|---|---|
| Naked Eye (Earth) | Clear night sky | ~5,000 | Limited by atmospheric scattering and light pollution; all within ~4,000 light-years |
| Small Telescope | Backyard 8-inch reflector | ~14 million | Reveals fainter stars and the star clouds of the Milky Way's disc |
| The Milky Way | Our home galaxy | 100β400 billion | Gaia satellite has individually catalogued over 1.8 billion; total estimated via mass |
| Local Group | ~80 galaxies inc. Andromeda | ~1β2 trillion | Andromeda alone contains an estimated 1 trillion stars |
| Virgo Supercluster | Our local supercluster | ~200 quadrillion | Contains ~100 galaxy groups and clusters across 110 million light-years |
| Observable Universe | Full 46.5 Bly radius sphere | ~200 sextillion | 2 Γ 10Β²Β³; ~2 trillion galaxies averaging ~100 billion stars each |
Stellar Distribution: The Red Dwarf Factor
When astronomers count "stars," they are counting objects ranging from tiny, dim red dwarfs barely massive enough to sustain nuclear fusion to giant blue supergiants burning a million times brighter than the Sun. The distribution matters enormously for questions about planetary habitability, galaxy lifetimes, and the ultimate fate of the cosmos.
Red dwarfs (spectral class M) are the universe's dominant stellar type. They are so dim they are entirely invisible to the naked eye β even Proxima Centauri, the closest star to our Sun at just 4.24 light-years away, cannot be seen without a telescope. Red dwarfs are extraordinarily long-lived: a 0.1 solar-mass red dwarf will burn steadily for ten trillion years, roughly 700 times the current age of the universe.
Sun-like stars (spectral class G) represent only about 7% of the total, but their moderate size, temperature, and lifespan make them a primary focus in the search for life-supporting planetary systems. The Sun itself is in the top 10% of stars by mass β the universe's stellar population is overwhelmingly composed of smaller, cooler, longer-lived objects.
Blue giants and supergiants (class O and B) are the universe's most spectacular but rarest objects. They burn through their hydrogen fuel in just a few million years, ending their lives in supernova explosions that forge and disperse the heavy elements necessary for planets and life. Despite their rarity, they dominate the visual appearance of star-forming galaxies.
Our Galaxy: Context Within the Milky Way
Before zooming out to the full universe, it is worth grounding the numbers in our own galaxy. The Milky Way is a barred spiral galaxy approximately 100,000 light-years in diameter and around 1,000 light-years thick at the disc. We are located in the Orion Arm, roughly 26,000 light-years from the galactic centre.
Current estimates place the Milky Way's stellar population at 100 to 400 billion stars. The European Space Agency's Gaia satellite, which has been systematically cataloguing stellar positions and motions since 2013, has individually measured the parallax and proper motion of over 1.8 billion stars β the most precise and comprehensive stellar census ever conducted. Even Gaia's extraordinary reach covers only a fraction of the galaxy's full volume; the galactic centre is obscured by dust, and the far side of the Milky Way remains poorly mapped.
"If the Milky Way were shrunk to the size of Europe, the distance between stars would be roughly the distance between cities β and the observable universe would be larger than the entire Solar System."
β Scale analogy, ESA / Gaia Mission documentationInterestingly, the Milky Way is in the upper tier of galactic size. The majority of galaxies in the universe are small dwarf galaxies β irregular or elliptical objects containing anywhere from a few million to a few billion stars. The Large and Small Magellanic Clouds, the Milky Way's closest satellite galaxies, contain approximately 30 billion and 3 billion stars respectively.
The Observable Universe vs. The Full Universe
Every number in this article refers to the observable universe β the spherical region of space from which light has had time to reach Earth in the 13.8 billion years since the Big Bang. Because the universe has been expanding throughout that time, the edge of the observable universe is currently about 46.5 billion light-years away in every direction β even though the universe is only 13.8 billion years old. Space itself has expanded, carrying distant objects further from us than the light-travel distance alone would suggest.
Beyond the observable universe, the cosmos almost certainly continues β possibly forever. The inflationary universe model suggests that the full universe could be at least 10Β²Β³ times larger than our observable patch, meaning the total number of stars in existence could be incomprehensibly larger than 200 sextillion. Some models of eternal inflation suggest an infinite universe with infinite stars β a concept that moves from astrophysics into cosmological philosophy.
The observable universe is bounded by the particle horizon β the maximum distance from which light could have travelled to us since the Big Bang. Stars beyond this boundary are not merely hard to see; they are fundamentally unobservable by any means in a universe with a finite age.
Due to the accelerating expansion of the universe (driven by dark energy), distant galaxies are receding faster than light. This means our observable universe is gradually shrinking β new galaxies will never enter our view, and currently visible ones will eventually fade beyond reach.
A Brief History of Star Counting
The attempt to enumerate the stars is almost as old as astronomy itself. What has changed over four centuries is not the desire to count, but the tools, methods, and conceptual framework available to do so.
c.150 AD β Ptolemy's 1,022
Ptolemy's Almagest catalogued 1,022 individual stars grouped into 48 constellations, compiled largely from the earlier work of Hipparchus (~129 BC). These were not counts of "all the stars" but of those visible and distinct enough to catalogue. The concept of uncountable stars was understood philosophically but not measured.
1610 β Galileo's Telescope Reveals Multitudes
When Galileo pointed his telescope at the Milky Way in 1610 and published his findings in Sidereus Nuncius, he discovered that what appeared as a diffuse band of light was in fact composed of countless individual stars too faint to resolve with the naked eye. The conceptual leap was immediate: the universe was far more populated than anyone had imagined.
1785 β William Herschel Maps the Galaxy
Herschel attempted the first systematic "star gauge" β counting stars in different directions to map the shape of the galaxy. He concluded correctly that the Milky Way is a disc-shaped structure, though he incorrectly placed the Sun near its centre. He estimated the galaxy contained roughly 300 million stars.
1924 β Hubble Discovers Other Galaxies
Edwin Hubble's measurement of Cepheid variable stars in the Andromeda Nebula proved it was far beyond the Milky Way β a separate galaxy in its own right. This single observation multiplied the estimated stellar population of the universe by billions, establishing that the universe is a vast collection of island galaxies, not a single stellar system.
1995 β Hubble Deep Field
The original Hubble Deep Field β a 10-day exposure of a tiny, apparently empty patch of sky β revealed approximately 3,000 galaxies. It was a watershed moment, demonstrating that every dark region of the sky contains distant galaxies, and that the universe's galaxy (and therefore star) count was far higher than previous estimates.
2016 β 2 Trillion Galaxies
Conselice et al. published their analysis in The Astrophysical Journal concluding the observable universe contains at least 2 trillion galaxies β more than ten times the previous estimate of 200 billion. The revision dramatically increased the star count estimate to its current value of ~200 sextillion.
2022βPresent β James Webb Space Telescope
JWST has begun detecting galaxies at redshifts beyond Hubble's reach β including surprisingly massive, fully-formed galaxies in the very early universe that challenge existing formation models. Its data will continue to refine galaxy counts and may require further upward revision of the total star estimate in coming years.
Why the Number Keeps Changing
The 200 sextillion figure is not a fixed, settled fact β it is a living estimate that has already changed dramatically in the past decade and will almost certainly change again. Several forces push the number in different directions simultaneously.
JWST is detecting galaxies at higher redshifts than ever before, including objects in the universe's first few hundred million years. Some of these early galaxies are unexpectedly massive and luminous, potentially adding to the total galaxy β and star β count.
Faint dwarf galaxies are systematically undercounted because they are too dim to detect at cosmological distances. As surveys improve, the number of detected low-mass galaxies increases, raising the total star estimate.
The universe currently forms approximately 1.5 new stars per year in the Milky Way alone, and billions across the observable universe. Meanwhile, massive stars end their lives in supernovae, and smaller stars slowly cool into white dwarfs and black dwarfs over trillions of years.
As the universe expands and dark energy accelerates that expansion, distant galaxies recede beyond our observable horizon. Stars that are currently β just barely β within our observable universe will eventually pass beyond the point where their light can ever reach us.
The peak of cosmic star formation occurred approximately 10 billion years ago, during a period astronomers call "cosmic noon." The star formation rate at that epoch was roughly ten times higher than it is today. The universe is in a slow stellar sunset β fewer new stars are being born, and the existing population will gradually die over the next tens of trillions of years.
Frequently Asked Questions
No. It is a central estimate with significant uncertainty β the true value is likely between 10Β²Β² and 10Β²β΄. The figure represents the best current scientific consensus derived from multiple independent methods that agree within an order of magnitude. Future telescope surveys will continue to refine it.
On a perfectly clear, dark night away from light pollution, the human eye can detect approximately 5,000 individual stars. With binoculars that number rises to around 200,000. All naked-eye stars are within a few thousand light-years β a tiny bubble within the Milky Way's 100,000-light-year diameter.
Current estimates place the Milky Way's stellar population at 100 to 400 billion stars. The ESA's Gaia mission has individually catalogued over 1.8 billion stars with precise positional data. The total is derived primarily from the galaxy's estimated total mass minus contributions from dark matter and interstellar gas.
A human body contains approximately 7 Γ 10Β²β· atoms β about 35 million times more atoms than there are stars in the observable universe. So no: stars are outnumbered by atoms in a single person. However, if you count all atoms in all humans alive today, you would still outnumber the stars by a factor of roughly 10 million.
Almost certainly yes. The observable universe is just the sphere from which light has had time to reach us. The full universe almost certainly extends far beyond β inflationary cosmology suggests it could be astronomically (or even infinitely) larger. The stars in those unobservable regions are not counted in the 200-sextillion figure.
Data from the Kepler Space Telescope suggests that on average, every star has at least one planet. Some estimates suggest there may be more planets in the Milky Way than stars β potentially 100 billion or more. Extrapolating to the full universe, the number of planets in the observable cosmos likely exceeds 10Β²β΄ β more than the number of stars.
By mass, the Sun is actually in the top ~10% β most stars are smaller, cooler, dimmer red dwarfs. By luminosity, the Sun is above average. By lifespan, the Sun's ~10 billion year main-sequence lifetime is modest; red dwarfs can burn for trillions of years. In the context of all stars that have ever existed, the Sun is moderately large and unusually bright.
The 200 sextillion figure is not a settled fact but a continuously refined estimate β one that has already been revised dramatically in the past decade and will evolve as the James Webb Space Telescope maps the early universe in unprecedented detail. It describes only the stars within the observable universe: the sphere bounded by 13.8 billion years of light travel time. What lies beyond that horizon β more stars, more galaxies, perhaps an infinite cosmos β remains one of science's deepest open questions.
NASA Universe Exploration
Direct access to NASAβs dedicated portal for the study of the cosmos. This resource provides technical data on galaxy formation, dark matter filaments, and real-time mission briefings from the James Webb Space Telescope regarding the total stellar population of the observable universe.
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