Dr. Cecilia H. Payne-Gaposchkin, 79, Phillips professor of astronomy emeritus at Harvard University and an authority on variable stars, died Thursday at a hospital in Cambridge, Mass. She had cancer.

The first woman to earn a doctorate from Harvard, Dr. Payne-Gaposchkin aslo was the first tentured woman professor there. She joined the university faculty in 1923 and was chairman of the department of astronomy from 1956 to 1960.

In a recent tribute, Harvard astronomy Professor Charles Whitney called her the greatest woman astronomer in history.

Early in her career, Dr. Payne-Gaposchkin helped perfect techniques for analyzing the luminosity of stars photographically. These techniques are widely used today and provide astronomers with valuable information about the composition of stars.

Dr. Payne-Gaposchkin's field of specialty was variable stars -- especially "pulsating" stars called cepheid variables and "exploding" variable stars called novae. Those stars vary in brightness because of changes in their internal makeup. Measuring the light and velocity of these stars helps astronomers determine distances on a galactic scale. Such measurements help scientists answer questions about the origin of stars and planets.

A native of Wendover, England, Dr. Payne-Gaposchkin earned a bachelor's degree at Cambridge University. She earned a master's and a doctorate from Radcliffe College, which honored her with an Award of Merit.

She was the first person to receive the Annie J. Cannon Prize, established in 1933 to recognize exceptional women in astronomy and, in 1977, was the first woman invited to give the Henry Norris Russell lecture at the American Astronomical Society meeting.

Her husband and colleague, Dr. Sirgay Gaposchkin, was an assistant at the Harvard Observatory, and a son, Edward, is a lecturer on astronomy at Harvard.

Dr. Payne-Gaposchkin, who lived in Lexington, Mass., was a member of the American Philosophical Society, the American Academy of Arts and Sciences, and the Royal Astronomical Society.

Besides her husband and son, Edward, survivors include another son, Peter, and a daughter, Katherine.