Bill Gleason, age 12, of Rochester, N.Y.,

 What is the life story of a star?

The main constellations were named in prehistoric times and the stars have not changed much since the human family began. Nevertheless, each star has a beginning and an end and goes through a changing life story lasting billions of years. Our time on earth is too short to observe these changes and we only can form theories as to what really happens. The branch of astronomy dealing with the history of the heavens is called cosmogony and theories are based on known facts, though we cannot prove these theories to be true.

Heat energy can be measured in weight, A light bulb burning day and night for a million‑years gives off about half an ounce of heat energy. The sun gives off four million tons of heat energy every second, day and night. This star of ours, like all stars, is a nuclear powerhouse converting hydrogen into helium. In the process, the sun is constantly losing its mass as surplus hydrogen gas is turned into energy.

The sun, like all the stars, is burning up its fuel and must therefore be changing. The process, however, is on an immense scale which is why we can get no information about the life story of a star by direct observation. The experts can estimate changes, however, from their knowledge of physics. They tell us that the sun has changed little in the past ten billion years and will not change much during the next ten billion years.

There are several theories concerning the life story of a star, and most of them agree as to the major events. The average star most likely begins as a hazy cloud of hydrogen gas, the most plentiful material in the universe. For some reason, the gaseous cloud begins to contract ‑the widely separated gas particles become closer together, The hazy cloud becomes a big sphere.

The denser gas becomes hotter and the forces of gravity come into play. Some say about half of this new energy is radiated into space and half goes into the star to make it hotter. The young star continues to shrink and becomes a nuclear furnace as heat and pressure work on the atoms in its seething interior. It begins to shine in the heavens as a giant or supergiant, brighter and perhaps hundreds of times bigger than our sun. After about half a billion years, the young giant shrinks to a star like our sun, of medium size and density. In this stage it exists for many billions of years without much change.

Meantime, more and more of the stars mass is changed into energy and radiated away into space. And finally the star collapses like the burned‑out ashes of a coal fire. For a short time it may become hotter, then it becomes a cold, dead lump of matter, The dwarf stage of old age in the life of a star is estimated to last only about 100 million years.