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

The exact number of stars that are visible to the naked eye is 5,766, and this number was calculated years ago. The calculation was the result of a survey of stars using a telescope carried out by a Prussian astronomer named Friedrich Argelander in Bonn, Germany, during the early 1860s. The astronomer is the first one to start a study on the variable stars, which are stars that have enough brightness to reach the Earth.

Argelander’s telescope had a lens of 3 inches (75 millimeters) in diameter, which is considered advanced in that period. Of course, the only starts that he could survey are those that could be seen from the city of Bonn. Still, in the report compiled by Argelander, the total number of stars that he was able to count was 324,000. This report was published in a star catalog known as the “Bonner Durchmusterung,” which was in print from 1859 to 1862.

After he finished the survey, he went to the lands in the south and examined the stars visible there. It is important to note that the stars visible in the area were not visible in the Northern Hemisphere, which is where the city of Bonn is. Ultimately, by combining both his survey in the Northern and Southern Hemispheres, he was able to count approximately of 1,720,000 stars. Furthermore, this was during the time when photographs were not yet used to count stars, so Argelander’s way of counting them seems to be an incredible feat since he only relied on his eye and his knowledge in physics, astronomy, and mathematics to determine the number of stars seen in the two hemispheres. The two reports are believed to have been the last of surveys conducted without the use of cameras and photographs.

However, the figure presented by Argelander was not the final calculation, as more powerful telescopes developed in the years after Argelander’s research allowed astronomers to view and count more stars. Unfortunately, it is also due to the advancement in telescope technology that people realized that it is impossible to count the stars one by one, as there can be billions of them, and some would even disappear from view after a few days. In addition, the total number of stars kept on increasing and doubling due to the telescope’s optical power. Each photograph taken with the telescope with a long exposure feature contained hundreds and even thousands of stars. Because of the sheer number of stars observed by the telescopes, it would take months for a patient and hardworking astronomer to count all the stars on one photograph while hundreds of more photographs would be awaiting the analysis each day.

Thankfully, the British astronomer named Edward Kibblewhite solved this vexing star counting problem. He invented a method that made star surveys work easier and conducted faster by using computer analysis and laser pointers. In order to make the lasers work, Kibblewhite did not use the positive prints of the photographs taken by the telescopes; instead, he relied on the negatives. These negatives are said to bring out stars as black dots and the empty spaces as a white background, making it easier for a person and a laser to count the dots.

Under a computerized manipulation device, the astronomer got a fine beam of helium-neon laser to perform a sweeping motion over the negative photograph. The white background on the negative reflects the light of the laser brightly, but the black dots that represent the stars reflected the light dimly. While the lasers are performing the sweeping procedure, the computers recorded not only the existence of the stars and their numbers but also the magnitude of the stars’ brightness based on how poor they reflect the light on the laser through the negative photograph.

This special technique of surveying stars has helped astronomers to determine the number of bright heavenly bodies in the visible space. In fact, the technique was so effective that the number of stars discovered up to the end of the 20th century came out as 1 billion! No doubt that there must be a hundred times more stars in the cosmos, and many of them may have reflected light that has not even reach the Earth yet!

Additional reading:

Star count (Wikipedia)