Sun, Age of

The sun, the star of our solar system, is approximately 5 billion years old and midway through its stellar life cycle. In another 5 billion years, the sun will exhaust its supply of fuel and collapse in on itself. As with all stars, it will go through the stages of stellar evolution before finally cooling into a cold, dark mass, in which state it will remain for the rest of time.

The sun formed from a slowly spinning cloud of dust and gas. The cloud eventually began to collapse under gravitational force, compressing itself into a smaller form. As this happened, the cloud began to spin faster, as stated by the law of conservation of angular momentum. The cloud of dust, as it continued to compress, began to flatten, forming a bulge in the center. This bulge formed the sun, making up 99% of the mass in our solar system. Meanwhile, the flattened, outer areas of the cloud surrounding the sun amalgamated, forming the planets and spatial debris (the remaining 1% of our solar system) while maintaining their spin, or rotation, around the sun.

After the first 400 million years in its existence, the sun entered the stage known as the main sequence. The sun will spend the majority of its existence as part of the main sequence, where it is today. After its becoming a star on the main sequence, gases and debris around the sun formed planets, becoming our solar system, roughly 4.6 billion years ago.

In about 3 billion years from now, the change that continuously occurs in the sun's core will be seen on its surface. Its main fuel supply will be exhausted and will switch to a secondary fuel, burning brighter at hotter temperatures. This will be the beginning stages of the sun transforming into a red giant. As the sun transforms into a red giant, the sun's mass will decrease as it emits stronger solar winds.

In 5 billion years, the sun's temperature will rise to 100 million Kelvin (K). The sun will expand beyond the orbit of Mercury and Venus, and life on Earth would be rendered impossible. The outer shell enveloping the sun will be blown off, and the debris and gases will surround the collapsed sun, creating a planetary nebula. The sun, now a white dwarf, will be the size of Earth, and will continue to consume its fuel supply over several billion years. Once the fuel supply is exhausted, our sun will become a frigid, black mass known as a black dwarf.

Scientists have measured the age of the sun by observing seismic waves on the surface. These seismic waves carried information about the sun's core to the outer surface. By observing these oscillations, scientists can compare information about the sun with theories of stellar evolution and stellar structure to give an estimate of the sun's age. It was dated at roughly 4.5 billion years, which corresponds with the age of the solar system through other studies such as nucleocosmochronology.