A Unique Sight? Every Night.

 Change is inevitable in our lives. We are born and grow older and taller. We might have children and we’ll watch them grow and change. Our hair eventually turns grey, or in my case, falls out. Our eyesight may fade, our joints may become stiffer.

 We grow older as does everyone we know and care about. Birth and death are a constant part of our world. Day turns into night; spring turns into summer. The clothes we wear at different times of the year, even the fashions we wear now as opposed to just a few years ago. But those changes are superficial.

 Would you like to see an absolutely unique sight? One you’ve never seen and one you’ll never see again? Wait until it gets dark, go outside, and look at the night sky. Do you see it? It has never been seen before, and never will again. It is tonight’s sky.

 The sky has never looked exactly as it does tonight and will never do so again.

 We think of the night sky as being constant. Oh, sure, the constellations move across the night sky from east to west, just like the sun in the daytime. The constellations visible in the night sky now will be almost completely different in six months. But, every April 15^th, we see the same stars. The sun will rise in a slightly different location tomorrow than it did today, but in one year, it will return to where it rose this morning.

 But the night sky changes in a way that all those seeming cycles never actually repeat. As the planets move in their annual dance around the sun, their pattern in the sky constantly changes. You’ll never see the exact arrangement of the planets again that you will see tonight.

 

The planets orbiting our sun.

Our planet’s poles slowly move so that the North Pole points to different stars over time, a motion called precession. This means the North Star we have now, Polaris, won’t always be our North Star. That creates subtle changes in the night sky over a 26,000-year period.

 

Precession and the path of the North Pole in the night sky.

 Our sun orbits the center of the Milky Way galaxy, so the exact pattern of stars in the night sky slowly changes. All other stars move under the various gravitational influences that direct their motions as they, too, orbit around the Milky Way.

 New stars are born and old stars die, sometimes with a dramatic effect.

 

The Great Nebula in Orion, where new stars are forming.

 

The Crab Nebula, the remains of a star that died in a supernova explosion.

 

Galaxies move through the universe, sometimes colliding. The larger galaxy then absorbs the smaller galaxy, gaining from the cannibalized galaxy the stars and gas clouds, the places where new stars come into being. Most of those new stars will have new planets orbiting them. Some of those planets will likely create new living beings.

Two galaxies colliding. They will eventually merge into one.

Change is the one constant in our lives. Even our night sky is eternally, if slowly, evolving.

This is the true magic of astronomy. You never get reruns. Each night remains unique. So, enjoy this night sky, because it will be different than any other night throughout time.