On a recent hike, while looking out for snakes and occasionally losing all sense of time and place, my thoughts settled on the endless examples of the cycles of life we find all around us. Huge trees, once spectacular, were now broken and decaying, giving life to countless organisms. Bird nests reminded me that, for some, regeneration is always a top priority. The occasional sound of running water directed my view to fresh greenery that, I hoped, would soon be replicated throughout the desert. 

As it is on our planet, so it is in space. Strange as it seems to think of life cycles where no evidence of life has yet been detected, for nearly 14 billion years stars have also taken part in this never-ending process.

Like us, stars vary greatly. And, like us, what they look like in their infancy is not what they look like after many years have passed. It appears that a star’s size largely determines how its life will play out.

The energy we associate with stars comes from the fusion of hydrogen atoms into helium. Over time, though, the hydrogen begins to deplete. For a star smaller than the sun, it’s a slow decay that ends with the star shrinking to the size of a planet. Dense and hot, but without the power of its youth, it becomes a white dwarf.

Sun-sized stars take a different path. As they lose their hydrogen, helium begins to fuse into carbon. This causes the star to expand and cool. In, perhaps, a billion years, the sun will undergo this change. It will turn into a red giant, becoming so large that its size will swallow the Earth. And then, after its outer shell blows off into space, like its smaller cousins, it too will collapse into itself and be renamed as a white dwarf.

The real big stars go through the most trauma. Many times larger than the sun, they eventually go supernova, an explosion that can be seen across the galaxy. What is left from this cataclysm condenses to something much more compact than any white dwarf. The remnants of these massive stars, sometimes measuring just several miles across, are so heavy that just a teaspoon of their cores weigh a billion tons. They have become neutron stars. Further, some of these objects, highly magnetized, emit incredible streams of light. We call them pulsars.

From clouds of condensing gas, stars are born, produce energy for billions of years and then cycle into something very different. The majority of them are called “main sequence” stars. Based on color and temperature, they are assigned to one of seven lettered labels. Bluish stars—O, B, A—are the hottest. Blue/white “F” stars come next. Our sun falls under the “G” rating, given its white/yellow color. “K” stars appear orange/red. Finally, “M” stars are unmistakably red and are the coolest, coming in around 5000 degrees Fahrenheit.

We revel in their differences. We marvel at their stages of life. In stars we see that nothing stays the same. Everything changes. Their ends are predictable and that, really, is rather soothing. 

As I continued my hike I tried to reconcile the amazement I have for the natural cycles of life with the man-induced climatic degradations our planet is experiencing. I marvel at the supernovas, but cringe at the rising level of carbon dioxide. I fear for our future.

I’ve often wondered what benefit is derived from the study of astronomy. It’s not like the science that gives us life-saving vaccines, or the engineering that gives us life-altering modes of transportation. But yet, everything about astronomy, from the billions of galaxies containing trillions of stars, to the ever-growing number of known planets orbiting those stars, brings us back to our own little rocky world. 

For me, astronomy isn’t the study of distant objects in an endless, remote universe. Astronomy is a means to see our place in all of it, to realize that we are, incredibly, both observer and participant. Maybe, by following the stars we will have a better appreciation, and be more protective, of the life cycle of our own place among them.