One of the more intriguing aspects of astronomy is that it teaches us a year is not actually a year. More specifically, a calendar year (365 days) is not equivalent to an astronomical year (roughly 365.25 days), which is why we must (triple word score alert) intercalate an additional day into the calendar every four years to make up the difference. Thus, for those of us who observe the modern Gregorian calendar, the quadrennial appearance of February 29 will go down in just six days.

Except that, strictly speaking, February 29 isn’t a quadrennial event. A Gregorian leap year is observed every four years except in century years. Thus, the year 1900 was not a leap year. However, every fourth century year is a leap year, so the year 2000 included a February 29. Why all the conditional intercalation? Because an astronomical year isn’t precisely 365.25 days — it’s closer to 365.2425 days, or 365 days, 5 hours, 49 minutes, and 12 seconds. The intercalated adjustments are made to ensure that the vernal equinox stays on or about March 21 of every year.

Yet for all these allowances, the modern Gregorian calendar is still inaccurate, as the astronomical year isn’t precisely 365.2425 days long. A recurring margin of error is building in the leap year system that suggests it will fail — as in, the vernal equinox will be more than a day removed from March 21 — at a particular date in the future.

IN WHAT YEAR WILL THE GREGORIAN LEAP YEAR SYSTEM “FAIL?”

Remember the Y2K bug suffered by legacy computer systems? Well, there’s a Y8K bug built into the Gregorian calendar, as it will likely fail to observe the vernal equinox anywhere near March 21 of the year 8000.

The average marginal difference between the actual astronomical year and the assumed astronomical year is 0.000125 days. Astronomer John Herschel famously proposed intercalating an extra leap day in the year 4000 to compensate for the Y8K calendar bug, but this solution was not adopted — and for more reasons than simply having almost a couple of millennia yet to make the decision.

The astronomical year is not a static interval of time, as there are tiny, random variances in the length of days and years. First and foremost, days are generally getting longer, as the braking force of Earth’s tides is slowing the rotation of the planet. Major earthquakes have a similar effect. While the changes are usually measured in microseconds, the aggregate variance over the course of centuries cannot be accurately modeled, let alone predicted.

The complex gravitational interplay of the planets in our local solar system also causes acceleration and deceleration of Earth’s progress around the sun. Add to that the gradual loss of mass by the sun itself, and the complex interactions of solar wind, gravitational radiation, and non-planetary objects make the collective force exerted on the Earth impossible to model over multi-century timespans. It should go without mentioning that, while these forces generally make years and days longer, they occasionally speed them up, as well.

Put more simply, the Year 8000 bug in the Gregorian calendar may not matter because there is enough error in the system already that we may need to add or even subtract a day from the calendar long before then, or perhaps make no changes at all, as the errors may cancel out over time.

That’s not just a confusingly counter-intuitive chronology; it’s an astronomically asymmetrical adage of Geek Trivia.

## The quibble of the week

If you uncover a questionable fact or debatable aspect of this week’s Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best quibble from our assembled masses and discuss it in a future edition of Geek Trivia.

Get the quibble.

This week’s quibble comes from the Feb. 10, 2012 edition of Geek Trivia, which asked why (and how) did the real-life US government rule that the fictional X-Men aren’t human?

Apparently, I’m subconsciously at war with the grammar police, as member byte^me found yet another basic flaw in my sentence construction:

I don’t know if this qualifies as a quibble or not, but you have an editing issue. You say “This is pretty strange, and not just because neither Spider-Man nor the Fantastic Four are mutants — they’re human beings granted superpowers via cosmic rays and a radioactive spider bite, respectively.”

However, you have it reversed. When you use the word “respectively,” that implies that the order of the items match between the two parts. They way you have them ordered, your statement says that Spider-Man got his powers from cosmic rays and the Fantastic Four by a radioactive spider bite.

That could make for an interesting “What If?” issue but that’s not how things happened in the Marvel universe.

I would probably buy that What If…? issue. It can’t be worse than the one where Wolverine becomes king of the vampires. Thanks for the correction, and keep those quibbles coming!