How many stars in the universe?

Campers attending Libertyville Recreation Department's Teen Travelers Summer Biking Camp had these questions about astronomy: "How many stars are there?" and "What color are the stars?"

Many of the planets, including Mercury, Venus and Mars, and stars in constellation, such as Leo, Taurus and Gemini are visible in the spring night sky.

Can't tell the difference between Cassiopeia, Canis Minor or Draco? Information about stars is easily found at your local library, especially if you live in Lake County, where Lake County Astronomical Society members tour local libraries each month, calibrating their high-powered telescopes in the parking lots so patrons can observe stars, planets and galaxies.

Gazing into the vast and never-ending heavens at night can inspire many questions about the universe.

Nadine Barlow, astronomy department chair at Northern Arizona University and director of the NAU/NASA space program, appreciates peering through the school's telescopes, including the 120-year-old telescope used in the 1930s to discover Pluto.

"I enjoy checking out any of the planets or the moon when observing through a telescope. Whether it is watching how lunar features appear to change because of changing shadows throughout the course of a day on the moon, checking out changes to the atmospheric storm systems on Jupiter, watching for dust storm activity or the seasonal changes in the sizes of the polar caps on Mars, or just admiring Saturn's magnificent ring system, the views are always different from one time to the next," she said.

Based at NAU in Arizona's San Francisco mountain range some 12,000 feet in elevation, Barlow offered these responses to reader questions about stars.

How many stars are there?

"Astronomers don't exactly know how many stars there are because nobody has the time to count all of them," she replied.

There are estimates. Astronomers use math to make the educated guess that the skies are brimming with a stratospheric 10 billion billion stars.

Here's how she calculated that number:

Number of galaxies in our universe (estimated): 2 trillion (2,000,000,000,000)

Number of stars in a galaxy (estimated): 100 million (100,000,000)

2 trillion galaxies x 100 million stars per galaxy = 10 billion billion stars in the universe (10,000,000,000,000,000,000).

Barlow emphasizes this could be a lowball guess - the numbers could shoot upward of 1 billion trillion.

"It is a lot of stars," Barlow concluded.

How about star color?

Gleaming white dots of varying sizes seem to spread across the sky. A closer peek with a telescope reveals color variations, Barlow explains.

"Stars typically look white, but in reality have different colors depending on their surface temperatures. Hotter stars look bluish, while cooler stars are reddish. Our sun, which has a surface temperature of about 6,000 degrees, is yellow. So stars can display the same range of colors that we see in a rainbow," she said.

Check it out

Cook Memorial Library in Libertyville suggests these titles on stars:

• "Star Light, Start Bright: Exploring Our Solar System," by Anna Prokos

• "Stargazing," by Alex Kuskowski

• "The Science of Stars: Exploring Matter," by Karen Latchana Kenney

• "Space Atlas, by Jirí Dušek

• "Night Sky Atlas," by Robin Scagell

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