Deep Time, Rhythms, and the Night Sky
I woke up early on a particularly cold August morning. Fall was on its way in the high country. My watch was missing in the somewhat disheveled tent, probably under Max, my yellow lab who was greedily trying to steal as much of my sleeping pad as possible. I’m not quite sure how he did it, but there were many nights when I would wake up on the cold hard floor of the tent to find Max cozily snoring on my sleeping pad, even though he had a nice comfy pad of his own. I had no idea how much of the freezing night had passed or how much more I would have to endure. Shivering, I stuck my head out of the tent. The night was still dark, but I could see Vega and Cygnus low on the western horizon and I knew that before long – minutes, rather than hours – the warm glow of the sun would be rising in the east. The night sky tracks time. Like a celestial clock and calendar, it measures time over seasons, generations, and millennia.
Over the year, the night sky changes above us, a harbinger of the seasons. Right now, in November as the first snows blanket the Colorado Rockies, winter constellations are starting to appear, rising just after sunset. These in turn will give way to a new set of stars and constellations as spring approaches. By early April, the winter constellations are fading into the west in the early evening, signaling the end of cold nights and a promise of warmth. Soon, they will be rising with the dawn. Even during the day, awash in the brilliant light of our sun, the stars are there. Here in Colorado, in mid-June, the winter constellation of Orion is directly overhead at noon. Although they are never truly gone, only hidden, it’s bittersweet to see them go - like saying goodbye to a group of close companions.
But as the winter constellations dip into the west, turn and look east.
Summer Sky (via Stellarium)
There, rising, are the stars we wished well last fall. We’re reunited with the summer constellations of Cygnus, Hercules and Sagittarius. By Late June, the Summer Triangle of Vega, Deneb, and Altair will be high overhead. These are the stars of summer. They accompany us during nights at the beach, evening walks, and campfires. They are with us through ice cream, and peach season. They serve as a starry backdrop for our Fourth of July fireworks. But they too are destined to leave us. Too soon. By October the days are getting shorter. Our summer companions set into the western sky earlier and earlier every night. And the great hunter begins to push his shoulder – Bellatrix - above the eastern horizon. Orion and his neighbors, Gemini, Taurus, and Auriga have arrived. They’ll be with us for Christmas, New Years, and the cold dark days of February. Watching them move slowly west, night by night, gives the promise of spring. And so it goes. The seasonal cycle of stars. The passage of time, the yearly rhythms of our lives, are written in the night sky.
Time is also apparent in the night sky on a different scale - a vast, immense, nearly incomprehensible scale. It’s the time we experience thanks to the union of light and distance. Deep time. Light from stars and celestial objects like nebulae and galaxies travel to us from unimaginable distances. It takes hundreds, thousands, even millions of years or more to make the trip. The Hubble Space Telescope has imaged galaxies over 12 billion light years away. So, what we see when we look at these objects or capture them with our cameras is how they appeared in the distant past. We literally look back in time when we stargaze. Incredibly distant time.
When we point a flashlight at the ground to light our way, the light hits its target at the same instant that we press the switch. But what appears simultaneous is not. Light travels at a speed of 186,000 miles per second so time elapses between pressing the switch and the light hitting the ground, probably about 3.3 nanoseconds, or 3.3 billionths of a second. Increase the distance and you increase the time. It takes 1.3 seconds for light to travel to us from the moon, 8 minutes from the sun. The reddish light from mars takes about 12 minutes on average. On clear nights under dark skies, the Andromeda galaxy is visible with the naked eye. The light that hits our eyes from that faint smudge started its journey 2.4 million years ago. That kind of time and distance connects us to the past in a way that is otherwise nearly impossible to comprehend.
Triangulum Galaxy. Light from this galaxy travelled for 2.7 million years before being captured by my camera. The red areas are concentrations of ionized hydrogen.
Two and a half million years ago an early ancestor of modern humans picked up a stone and used it to get to the meat of a tasty clam. They were one of the early adopters of this new stone-age technology. At the same moment, an electron in a hydrogen atom somewhere in Andromeda shifted in its orbit. That shift produced a photon that began speeding toward earth at 186,000 miles a second. Throughout our entire history - the emergence and evolution of Homo Sapien, extinction of the Neanderthals, the Bronze Age, the rise of Greek civilization, the fall of Rome, the dark ages, enlightenment, the industrial revolution – the photon travelled toward us. Finally, that tiny packet of old light, along with millions of others just like it, ended their trip as they struck the sensor of my camera, only to reemerge, ironically, as a tiny speck of light on my computer screen. A journey that began more than two million years ago culminates and comes to an end on a quiet night on a porch in Evergreen, Colorado. The stars that we see in the night sky, the images that I and other astrophotographers create, are legacies of an infinite number of similar events.
Before cell phones and watches and clocks, humans experienced time by looking up. We watched the movements of the sun, we tracked the motion and phases of the moon, and we studied the stars. Today, as we continue to lose our view of the celestial clock, our connection to the natural rhythm of our lives and our link to the distant past are diminished. Protecting night skies and reducing light pollution can help us maintain, restore, and better understand our ongoing inevitable relationship with time.