c. 4.6 Billion BCE

Birth of the Sun

The temperature and pressure in the central region of the Solar Nebula grew dramatically for about 100 million years, until they passed a threshold where hydrogen atoms were packed so tightly that they underwent nuclear fusion, becoming helium and releasing some energy as light and heat. Thus, our Sun was born!

We tend to think of the Sun as special, and rightly so—the Sun is critical to the creation and continuing survival of all life on our planet. It’s harder to think of the Sun as typical, average, even mundane, but in many ways it is. Our star is one of more than 10 billion trillion (1 with 22 zeros after it) stars in the known universe, all of which appear to be the natural result of matter—mostly hydrogen—interacting with gravity at high pressures and temperatures and releasing enormous amounts of energy into their surrounding space. Stars are truly the engines of our universe.

Once stars are born, they live relatively stable lives and then die, often in relatively predictable and sometimes spectacular ways. The Sun is no different. It will keep fusing hydrogen atoms into helium atoms for another 5 billion years or so. When the hydrogen runs out, the Sun will shed its outer layers (engulfing the Earth and the other inner planets) and start fusing helium in its core. When the helium runs out, the Sun slowly fades to a white dwarf and then dims to a cinder.

Astronomers have been able to deduce that about one to three new stars are born each year, and about one to three old stars die each year in our Milky Way galaxy. If we extrapolate to all known galaxies and do a little math, that means that something like 500 million stars are born and 500 million stars die each day in the universe. It’s a staggering and humbling thought that should make us appreciate even more every one of these precious days in the life of our own star, the Sun.

An ultraviolet image of our local star, the Sun, taken by NASA’s Solar Dynamics Observatory UV space telescope. Streamers, loops, hotter spots (brighter), and cooler spots (darker) are all evidence of an extremely active, though quite typical, middle-aged star.