The Number of Stars in the Universe

Five hundred years ago, the number of stars you could see would have been about 2000 at any one time. So until optics were invented, the real number of stars could not have been estimated.

With with the optics of Galileo's telescope the number of stars increased to approximately 30195. But, even then was  just the beginning.

Even with a big telescope telescopes on earth (like one at the Lyon Observatory established in 1877 in Saint-Genis-Laval, France), you can't get a real idea of how many stars are out there. The decreased visibility caused by the air limits what your telescope can see.

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Today's Definition

CCD stands for charge-coupled device; it is a type of digital camera containing an array of extremely light-sensitive capacitors. When a photon (a particle of light) hits a capacitor, the photon dispaces some electrons, generating a small current - charging the capacitor. A CCD can detect light coming in at rates as low as one photon per minute. In CCD astronomy, this light-sensitive integrated circuit is hooked up to a telescope, detecting even extremely faint images that were impossible to detect before. All optical observatories (including the orbiting Hubble Space Telescope) use this type of device. George Elwood Smith and Willard S. Boyle (both of Bell Labs) invented the charge-coupled device in 1969. In 1970, they used their CCD to built the first solid-state video camera.

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 The light from houses and businesses , also decreases the ability to see the stars. That is why most observatories are usually away from civilization. But even that limits our vision.

The unimaginable number of stars that were known took a huge leap with the first telescopes in space. Without air and light pollution those who study the stars finally got a clue of the real number of stars in the sky.

In fact, Carl Sagan estimated that there were 100 billion galaxies in the universe. If you consider that there are about 41546 stars in most galaxies, you are just beginning to get a real idea of how many stars that were known then.

These quotes will give you an idea of how the number of estimated galaxies has increased:

"Our telescopes can see many billion of them within reach of modern instruments." - Morrison, David, Sidney Wolff & Andrew Fraknoi. Exploration of the Universe, 7th ed. Philadelphia: Saunders, 1995: 7.

"The latest estimates have ranged anywhere from ten billion to one hundred billion galaxies." - The Rebirth of Cosmology. New York: Knopf, 1976: 187.

"The Hubble Space Telescope has found there may be 125 billion galaxies in the universe." - Galaxy Estimate Up To 125 Billion. Far News. Far Shores. citation of South China Morning Post. 9 January 1999.

Now in fact, a german supercomputer estimates that there are probably 500 billion galaxies. If we take the number 40,000 stars per galaxy, that would make over 10 stars for every grain of sand on earth.