Years ago, my dad, sister and I took a class in celestial navigation. You might wonder why anyone would do such a thing, but we all grew up sailing, and this was an opportunity to use some of the world’s oldest technology to navigate the ocean in the modern world. The final for the class was to use the Hayden Planetarium in the Boston Museum of Science — which we were all pretty excited about — to test our skills a few days before Christmas. The experience taught me a lesson far greater than the one the instructor probably intended.

The class was small. A handful of us filed into the planetarium. Christmas decorations lined the hall, but not above the lip where the planetarium dome started. The Hayden Planetarium was an analog system at the time — a giant mechanical device that spun and tilted with hundreds of lenses that focused light on the dome to create the illusion of a starry night.

The skyline of Boston was projected in the dome. Not for the first time, I wished the planetarium had been able to keep the original hand-built physical model of the skyline working, with its colored spire of the old John Hancock building, glowing Coca-Cola sign, and moving trolley. The projection, while not as quaint, was easier to keep up to date with an always-changing skyline.

As students, we gathered together and took out our sextants and tables. Our guide brought the sun up to noon. This was the easiest part of the test. We looked through the sextant lens — not needing filters as we would with the real sun — and sighted that artificial sun and horizon for the date, consulted our books and verified our latitude and longitude. Next up, we tested nighttime navigation. The guide darkened the room, and the stars twinkled brightly. We focused on the North Star on Christmas Eve and used red-light flashlights to look at our books, so we could still see in the dark.

With a small class, our finals complete, and plenty of time left in the dome, our guide asked us if we wanted to see anything. My classmates started asking to see what the sky looked like on the days of their birth. The machine whirred as the gears spun the device to display the requested dates.

Since we were going back in time, and it was Christmas, I asked what the sky looked like on that first Christmas day almost 2,000 years prior. The projector whirred and spun and tilted for a long time as the heavens spun and the years rolled back. Finally, we arrived on Christmas Eve. But something was wrong. We should have seen a similar sky to the present time, but it was off. The guide started rolling forward again, and a similar sky came into view.

The exact cause remains a mystery to me. It is possible the assumed date we started from was incorrect. However, there is also a good chance the device wasn’t really intended to give an exact view of 2,000 years ago. Analog machines like this one are often inexact.

Take, for example, the slide rule. When the Texas Instruments calculator came out, my dad and I raced to see who was faster — me on the calculator or him on his trusty slide rule. He had spent decades using that slide rule. It had helped figure out the trajectories of the Mercury, Gemini and Apollo capsules returning through the atmosphere, as well as the potentially deadlier vehicles that would hold nuclear warheads, all, fortunately, still sitting in their silos. My dad was fast, but his numbers were approximations. They were good enough for the intentions I listed, when used correctly and frequently, verifying the output of computers, but not giving the same six decimal places of precision as the digital calculator. Of course, my calculator wasn’t perfect either. It was, after all, also made by humans. Fractions, for example, could run to infinity.

That planetarium’s original beautiful model skyline, the intricate mechanical device that projected the stars and my dad’s simple wooden slide rule all displayed excellent craftsmanship. They were well-designed efforts from our fellow human beings. The attempt of excellence should always be recognized and celebrated, whether creating a mechanical device or, say, the wheels and gears of our system of government.

What humans create, however, often creates approximations — inventions that require us to watch for their limitations but which can still function and bring us joy. They can be replaced or updated, but that comes with its own limitations. Attempting perfection is worthy of our appreciation and admiration, but it can never be attained. To everyone, imperfect but trying, Merry Christmas and Happy Holidays.

Dr. David Ferro is dean of the College of Engineering, Applied Science & Technology at Weber State University. Twitter: @DavidFerro9

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