The Kepler space telescope looks for planets by measuring tiny decreases in the brightness of stars when planets cross in front of them.

VOA: special.2011.02.09

An astronomer at Harvard College, Henrietta Leavitt, had discovered that these periods of brightness could be used to measure the star's distance from Earth.

VOA: special.2009.04.29

Its reddish color and changes in brightness over time make the planet an unforgettable sight.

VOA: special.2010.07.28

Scientists say small changes in the sun's brightness can produce effects on Earth similar to two weather events in warm waters of the Pacific Ocean.

VOA: special.2009.09.29

Visitors can enjoy the brightness and color of the universe she created.

VOA: special.2010.04.14

Cepheid variable stars are stars whose brightness changes at regular periods.

VOA: special.2009.04.29

All the brightness fled from the boy's face.

VOA: special.2010.05.15

He studied their shape and brightness.

VOA: special.2009.04.29