Einstein Science Reporting for Kids
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American Association for the Advancement of Science

The Hubble Telescope lets astronomers see deeply into stars

Summer is a great time to sit outside and watch the heavens. The sky is full of stars. You can see planets and constellations if you know when and where to look.

The sky has fascinated people for centuries and many people have used the stars to guide them on boats or land. Astronomers study the skies to learn more about how and when the universe was formed.

Using the Hubble Space Telescope, scientists from Canada, the United States and Australia had a camera focused on a star cluster named NGC 6397 for five days to get very detailed pictures of some very faint stars there.

"The light from these faint stars is so dim that it is equivalent to that produced by a birthday candle on the Moon, as seen from Earth," says Harvey B. Richer the lead scientist from the University of British Columbia, Victoria, Canada.

By studying these pictures the astronomers to learn two important things and reported them in the 18 August issue of the journal Science.

They determined a dividing line to classify the two categories of stars there. The large stars that are still burning are about 80 times the mass of the planet Jupiter or larger. They are large enough to keep burning hydrogen inside them in a process called fusion -- the same process that keeps the Sun burning brightly. Stars that are smaller than the 80 times the mass of Jupiter are known as brown dwarfs. They were not large enough to start the fusion process and instead burned up their hydrogen.

The large stars have burned for billions of years, at least 13.7 billion years, and will continue. The smaller brown dwarfs did not live even a billion years.

The astronomers learned more about the remains of stars called white dwarfs. These are like the still-glowing coals in the barbecue grill. Scientists saw a change in the color of white dwarfs that shows them when the core of the star stops the fusion process.

These two bits of information will help astronomers learn more about stars and to determine the age of these globular clusters.