Astronomers announced today that there are 70 sextillion stars in the visible universe, or some 70 thousand million million million. That's a 7 followed by 22 zeros.
The figure paints an inadequate picture of the scope of the cosmos, however.
Other scientists have previously tried to pin down this most elusive of astronomical numbers. The new figure is 10 times more accurate than previous attempts, according to those who made it. Still, the researchers admit that it is just an estimate, based on surveying only a small patch of sky.
"This is not the total number of stars in the universe, but it's the number within range of our telescopes, said Simon Driver of the Australian National University. "The real number could be much, much larger still -- some people think it is infinite."
Zillions, for sure
A previous estimate, cited by NASA, put the figure lower, a 1 followed by 21 zeros. Another NASA Web site sagely puts the count at zillions, a word that does not represent a real figure but rather an "extremely large, indeterminate number." That presumes we'll never really know.
The new calculation was made by studying the brightness of a few galaxies in the relatively nearby region of the universe in one direction, in order to estimate how many stars each held. That was extrapolated to the entire universe.
The result is said to be more stars than there are grains of sand on all of Earth's beaches.
"Even for a professional astronomer used to dealing in monster numbers this is mind-boggling," Driver said while presenting the number at a meeting of the International Astronomical Union in Australia.
His research team included Jochen Liske of the Royal Observatory Edinburgh, Nicholas Cross from Johns Hopkins University, Warrick Couch from the University of New South Wales and David Lemon from St Andrews University.
Frustrating
Many factors frustrate the effort to count all the stars.
Telescopes cannot see individual stars in the most distant galaxies -- they just record blobs of light. In fact, the structures of the most distant galaxies that have been detected remain largely unknown. Astronomers do not know exactly when and how rapidly stars form as a galaxy develops, nor how many stars existed in the universe's earliest galaxies.
Further, stars are forming all the time, so the number is never fixed. Also, when telescopes are pointed at a galaxy that is, say, 10 billion light-years away, the light it detects left that galaxy 10 billion years ago. The galaxy has changed greatly since then, and astronomers can only guess at how it evolved -- and how many stars it might now contain -- by studying more mature galaxies closer at hand.
Finally, astronomers do not know if our apparent universe is the Universe. There may be much, much more out there that is not observable and never will be known.
If these are not enough problems, scientists even have difficulty counting the stars in our own Milky Way Galaxy. The figure is typically put at between 100 billion and 300 billion.
One thing is certain: We cannot see most of the stars that are out there.
Under very dark skies in remote locations on Earth, roughly 8,400 are visible to the naked eye, globally speaking. From any given location on a single night, about 2,500 are available to the discerning eye. Under bright city lights, the quantity of stars visible to the unaided eye can drop to mere dozens.
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