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Thursday, February 21 , 2019, 6:44 pm | Partly Cloudy 50º


Dennis Mammana: Big Dipper Through the Millennia

The Big Dipper is an optical illusion. Click to view larger
The Big Dipper is an optical illusion. (Creators.com illustration)

Years of living and working have taught me many lessons. But one lesson seems to be truer than most: Whatever is temporary is permanent, and whatever is permanent is temporary.

This applies everywhere — buildings, governments, relationships, etc. Things we’re convinced are everlasting are almost always destined to change. And things we’re told will be only temporary — taxes, detours, visits from in-laws — well, they often turn out to be permanent!

Even the heavens, which we humans perceive as eternal and unchanging, are only temporary.

While we often refer to the stars and constellations as being fixed — especially when we watch the moon and planets drift gracefully in front of them — they are actually moving in seemingly random directions at speeds of many miles per second.

Since the stars reside trillions of miles away, we’re not able to notice their movements over short periods of time, so we perceive them as fixed. If we are patient, however, we can see reality.

Take, for example, the stars of the Big Dipper, which appear high in the northern sky at this time of year. To most of us in the northern hemisphere, this celestial icon is one of the first star groupings we learn to recognize. Every scout has used it to locate the North Star and use it to navigate during the night.

The Big Dipper’s shape has been represented by various cultures throughout history, as a bear followed by three warriors, a wagon, a plow and (in Chinese culture) the government itself.

Its shape, sometimes called the “drinking gourd,” even served in song to inspire pre-Civil War slaves to flee to the North for freedom. We’ve come to recognize the seven stars of its bowl and its long, curved handle as a permanent sight.

But what we see as the Big Dipper is not real. It’s not a solid structure; it’s purely an optical illusion that occurs because of where we live in our galactic neighborhood.

If we could fly freely through space and travel to the other side of those stars, though, our perception of the Dipper would change as we travel.

The dipper shape is fluid over time as well. Its five central stars are stellar siblings. They were born from the same interstellar cloud some 500 million years ago, and still travel together at remarkable speeds.

But seeing this movement is another matter altogether. If we could accelerate time and watch this star grouping for tens of thousands of years, we would begin to see the Dipper’s shape change as its stars move through space.

A hundred thousand years ago, the first Homo sapiens in the Middle East may have recognized this stellar collection as a celestial fishhook, rather than a dipper. And our descendants a hundred millennia in the future will also see the shape of a dipper, but one that is distorted and reversed from what we see today.

So the next time you think about heading outdoors to enjoy stars and constellations, don’t put it off too long. Remember: Whatever is temporary is permanent, and whatever is permanent is temporary!

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. The opinions expressed are his own.

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