What is the exact number of stars? What method is used by the astronomers to count them?

The exact number of stars seen by naked eye is 5,766 and it was ascertained years ago. Thereafter, a survey of stars using telescope was carried out for the first time by a Prussian (German) astronomer named Friedrich Argelander in Bonn during the decade of 1860s. His telescope had lens of 3 inches (75 millimeters) diameter. Obviously he could survey only those stars which could be seen from the city of Bonn. Still, in the survey report compiled by Argelander their number shot up to 4,58,000. Thereafter, he went to the lands in the south and surveyed those stars that were not visible in the Northern Hemisphere. Ultimately he compiled a list of 10,72,000 stars. But this figure was not final. As more powerful telescopes were made more stars were discovered. So much so that it became impossible to count them one by one. The total number of stars kept on increasing in multiples of the telescope’s optical power. Each long exposure photograph taken with telescope contained hundreds of thousand stars. It would take months for a painstaking and patient astronomer to count the stars on one photograph whereas hundreds of more photographs would be awaiting the analysis.

Ultimately the British astronomer named Edward Kibblewhite solved this vexing problem. He invented a method that made the star survey work easier and quicker by using computer and laser. Kibblewhite did not take out positive prints of the photographs of various sectors of the space but used the negatives. Bright stars appeared as black dots against the white background in the negatives. Under computerized manipulation he got a fine beam of helium-neon laser sweep over the negative. The white background on the negative reflected the light of laser brightly but the black dots representing the stars reflected the light dimly. Meanwhile the computers recorded not only the existence of the stars but by measuring the degree of dimness in the reflection also recorded the magnitude of the stars’ brightness.

This technique of surveying has helped to take the number of stars discovered up to the end of the 20th century to 1 billion! No doubt there must be hundreds of times more stars in the cosmos and many of them such as whose light has not reached the Earth yet!

Additional reading:
Star count (Wikipedia)

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