How Old is the Sun?

Located about 150 million kilometers from the Earth is our closest star, the sun. Due to its immense power, the sun has been worshiped as a deity by numerous religions throughout human history from the ancient Egyptians to the ancient Mayans. The scale of the size of the sun is mind-boggling; one could fit 1.3 million earths in its 1.41*1018 cubic-mile volume. The circumference around the sun’s equator measures 4.379*106 ¬ miles which are equivalent to 109 times the earth’s circumference around the equator. The sun’s mass is a whole other ball game; the solar mass accounts for more than 99.8% of the total mass of the entire solar system. Contrary to what we see on earth, the sun is not stationary but is moving at a speed of 220 kilometers per second on its orbit around the Milky Way Galaxy, a journey that the sun takes at least 225 million years to complete.

Age of the Sun

The sun is the most ancient object in our solar system. The formation of all other objects in the solar system was based on the sun including all the planets, their respective moons, and all the asteroids. Scientists put the estimated age of the sun at 4.5 billion years which makes the sun a middle-aged star. The sun is expected to burn its current hydrogen reserves for another 5 billion years after which the sun will shift to burning on helium for another 130 million years. During this period, the sun is expected to grow in size and become a red giant whose immense size will see it engulf the orbits of the three closest planets; Mercury, Venus, and Earth. After the 130 million years, the sun is forecasted to collapse under its mass to form a white dwarf. During the sun’s white dwarf stage, it will be similar in size to the earth but with its original mass.

How Do We Measure the Age of the Sun?

One might ask how scientists are able to estimate the age of an object which - besides being over 150 million kilometers from earth, it is the hottest object in the solar system with a surface temperature of 5,800 K. It is impossible to measure the age of the sun or that of any other star due to the aforementioned challenges. However, scientists can forego the impossible task by employing an indirect way to calculate and estimate the age of the sun and that of other celestial bodies such as distant planets and stars. One way is through the use of computer models of the sun and the solar systems where such models are developed chronologically so that the age of the sun can be estimated to correspond to the period when the models have a similar composition as the sun currently has.

Use of Meteorites and Moon Rocks

Another method used to estimate the age of the sun is through the determination of the age of other ancient celestial objects found on earth such as meteorites. Moon rocks taken from the moon by astronauts during lunar space programs are also used to estimate the age of the sun as the surface of the moon has not changed for millions of years.