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Monday, October 25, 2021

How many stars are there in space?

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Curious Kids is a series for kids of all ages. If you have a question you’d like an expert to answer, send it to [email protected]


How many stars are actually in space? – Meesong, Brookline, Massachusetts


Look up at the sky on a clear night, and you’ll see thousands of stars—about 6,000 or so.

But this is only a small fraction of all stars. The rest are too far away for us to see them.

A picture of the sun.
The Sun is a star, which is closest to us – 93 million miles away.
Roman Studio / Moments via Getty Images

universe, galaxy, stars

Yet astronomers like me have figured out how to estimate the total number of stars in the universe, which is pretty much everything that exists.

There are galaxies scattered throughout the universe – clusters of stars, planets, gas and dust clustered together.

Like people, galaxies are diverse. They come in various shapes and sizes.

Earth is in the Milky Way, a spiral galaxy; Its stars are grouped in spiral arms that revolve around the center of the galaxy.

Other galaxies are elliptical – egg-shaped – and some are irregular, with different sizes.

An artist's concept of the curved spiral arms of our Milky Way galaxy.
Artist’s concept of a face-to-face look at the Milky Way. Note the spiral arms.
NASA/JPL
A nighttime photo taken in Utah's Canyonlands National Park looking up at the sky and revealing thousands of stars in the Milky Way.
A view of a small part of the skyline, from Canyonlands National Park in Utah.
National Park Service/Emily Ogden

counting galaxies

Before counting the number of stars in the universe, astronomers must first estimate the number of galaxies.

To do this, they take very detailed pictures of small parts of the sky and count all the galaxies they see in those pictures.

That number is then multiplied by the number of pictures needed to photograph the entire sky.

Answer: There are about 2,000,000,000,000 galaxies in the universe – that is, 2 trillion.

15,000 galaxies appear as tiny dots and spots in this NASA image of the night sky.
15,000 galaxies appear as tiny dots and spots in this NASA image of the night sky. There are billions of stars in each galaxy.
NASA/ESA/P.Oesch/M.Montes

counting stars

Astronomers don’t know exactly how many stars are in each of those 2 trillion galaxies. Most are so far away, there’s no way to tell exactly.

But we can make a good estimate of the number of stars in our Milky Way. Those stars are also diverse, and come in a variety of sizes and colors.

Our Sun, a white star, is medium-sized, medium-weight, and medium-hot: 27 million degrees Fahrenheit (15 million degrees Celsius) at its center.

Large, heavy and hot stars are blue in color, such as Vega in the constellation Lyra. Small, light and dim stars like Proxima Centauri are usually red. It is the closest star to us except the Sun.

A red dwarf star.
Artist’s concept of a red dwarf star with an exoplanet in orbit. About two-thirds of the stars in the Milky Way are red dwarfs. Exoplanet is the name of the world outside our solar system.
NASA/ESA/G.Bacon/STScI

an incredible number

Red, white and blue stars give off different amounts of light. By measuring that star’s light—specifically, its color and brightness—astronomers can estimate how many stars are in our galaxy.

By that method, they found that there are about 100 billion stars in the Milky Way – 100,000,000,000.

Now the next step. Using the Milky Way as our model, we can multiply the number of stars in a normal galaxy (100 billion) by the number of galaxies in the universe (2 trillion).

The answer is an absolutely astounding number. There are about 200 billion trillion stars in the universe. Or, to put it another way, 200 sextillions.

That’s 200,000,000,000,000,000,000,000!

The numbers are so huge that it is hard to imagine. But try this: That’s about 10 times the number of cups of water in all of Earth’s oceans.

Think about that the next time you’re looking up at the night sky—and then wonder what might be happening to the trillions of worlds orbiting all those stars.

NASA Video. Our Milky Way Galaxy: How Big Is Space?

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This article is republished from – The Conversation – Read the – original article.

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