How many stars are there in the universe?


Quick Answer

While the exact number of stars in the universe is unknown, astronomers estimate that there are at least 100 billion stars in each of the 10 trillion galaxies. However, new galaxies are discovered often.

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Full Answer

Trying to count the number of stars in the universe is like attempting to count the number of grains of sand on all of the beaches in the entire world. The task would be impossible. Even without proper equipment, people can see thousands of stars with the naked eye on a clear night. With a telescope, people can see even more. However, these are just the stars in the Milky Way galaxy. Scientists discover new stars and new galaxies all the time. If the universe consists of all of these galaxies put together, then that means scientists discover new stars often as well.

Stars in the Milky Way Galaxy
Earth is located inside the Milky Way Galaxy. This galaxy is home to over 300 billion stars. One way to estimate the number of stars in the universe is to use the Milky Way as an example and multiply the number of stars in the Milky Way by the number of galaxies in the universe. By estimating that there are one hundred billion or one trillion stars in the Milky Way and the same number of galaxies in the universe, the simple calculation results in up to one septillion, or 10 to the 24th power, of stars in the universe. Unfortunately, not all galaxies are the same size. The Milky Way is large in comparison to the millions of dwarf galaxies in the universe, and some galaxies are as much as 20 times larger than the Milky Way. Thus, there is still a lot of room for error in that estimation.

Stars Forming and Dying
Another factor that contributes to the number of stars in the universe is that stars are born and die every day. Again, the rate at which stars die and form varies. Space observatories around the world are able to chart the rates of star development throughout history to estimate the number of stars in the universe on any given day.

Advances in Technology
As technology becomes more advanced, astronomers are able to get a better picture of the universe. The Hubble Space Telescope performs imaging experiments to count galaxies. Astronauts have upgraded the telescope allowing it to see the galaxies even clearer than before. In 1995, the telescope faintly detected about 3,000 galaxies in a spot in Ursa Major. Less than 10 years later, with upgraded equipment, the telescope detected more than 10,000 galaxies in the same spot. As technology advances, the number of discovered stars in the universe continues to increase.

Because of the vast number of stars in the sky, the galaxy and the universe, no one attempts to count them individually. Instead, scientists use measurements and calculations to estimate the number of stars based on the data collected. As of 2017, the best estimate is there are 100 billion stars in each of the estimated 10 trillion galaxies, or one septillion stars in the universe. This number will only increase as technology advances and new stars and galaxies are discovered. Depending on the cloud cover and light conditions outside, people can expect to see only about 4,500 of these stars on a clear night.

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