A star is a massive, compact body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. The most familiar and closest star to the Earth is the Sun. Unlike a planet, from which most light is reflected, a star emits light because of its intense heat. Stellar astronomy is the study of stars.

Individual stars differ from each other due to their total mass, their composition, and their age. The total mass determines the course of evolution of a star, as well as its eventual fate. A Hertzsprung-Russell diagram shows the pattern of the temperature of stars against their absolute magnitude, and can be used to determine the overall age of a star and the stage in its evolution. Initially, stars are composed primarily of hydrogen, with some helium and heavier trace elements that determine the metallicity of a star. Over the course of a star's evolution, a portion of the hydrogen is converted into heavier elements through the process of nuclear fusion. Part of the matter is then recycled back into the interstellar environment, where it is used to form a new generation of more metal-rich stars.

Multi-star systems consist of two or more stars that are gravitationally bound, and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution. For example, a nova occurs when a white dwarf accretes matter from a companion star.

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NPR Topics: Space

Millionaire Follows Dad's Footsteps — Into Space
Thu, 09 Oct 2008 08:41:00 -0400
Richard Garriott, a famous video game developer, is paying millions of dollars for a ride on a Russian rocket to the International Space Station. He has wanted to go to space since he was a kid. His father and all of his neighbors were NASA astronauts. It's the first time the child of an American astronaut will blast off into space.
Young Galaxy's Magnetic Field Is Surprisingly Strong
Fri, 03 Oct 2008 13:53:00 -0400
Current models indicate that the magnetic fields that enclose galaxies grow slowly over billions of years. But scientists have used a telescope to peer back millions of years in time and discovered a distant galaxy with a magnetic field at least 10 times the average strength.
SpaceX Celebrates First Successful Rocket Launch
Fri, 03 Oct 2008 13:53:00 -0400
SpaceX's flagship Falcon1 rocket has successfully launched from an island in the central Pacific, becoming the first privately-developed rocket to orbit the planet. NASA has already contracted SpaceX to begin private space flight missions to the International Space Station beginning in 2010.
Computer Malfunction Delays Hubble Mission
Fri, 03 Oct 2008 13:31:00 -0400
NASA has postponed a planned repair mission to the Hubble Space Telescope after a new problem developed with the orbiting observatory. Ed Weiler, associate administrator of the Science Mission Directorate at NASA, explains why repairs won't take place until Feb. 2009 — at the earliest.
For Young Chinese, Spacewalk An Indicator Of Might
Sat, 27 Sep 2008 17:05:00 -0400
China on Saturday will become only the third nation — after Russia and the United States — to carry out a spacewalk. The event will be broadcast live nationwide. This milestone underscores China's technological achievements and is boosting national pride.
Solar Winds, Crucial To Life On Earth, Decreasing
Fri, 26 Sep 2008 12:45:00 -0400
Solar winds — invisible gas plasma emitted by the Sun — protect the solar system from cosmic rays that are hostile to terrestrial life. But new data from the Ulysses NASA probe indicate solar wind output is lower than has ever been previously documented.

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