General Astronomy 🔭 (genastronomy.blogspot.com)

Friday, February 28, 2020

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Wednesday, February 26, 2020

Speaking of Science: Our calendar’s expiration date

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Talk nerdy to us.

By Ben Guarino

Our calendar's expiration date

Johns Hopkins University astronomer Richard Conn Henry is not a fan of the Gregorian calendar, as he told me for a story this week about a new calendar he and a colleague, economist Steve H. Hanke, proposed. (Among other things, this 364-day calendar would do away with leap days and Oct. 31 — a tough sell, perhaps, for Halloween die-hards.) But, Henry said, the Gregorian system pretty accurately accounts for the Earth's relationship with the sun.

Leap days help keep the calendar accurate. They absorb the discrepancies between the time it takes for the Earth to orbit the sun (365 days, 5 hours, 48 minutes and 46 seconds) and the human need for a calendar of integer days.

Unaccounted fractions of a day cause the calendar to drift out of sync with seasons. Pope Gregory XIII changed the calendar in the 16th century. Back then, the springtime Easter holiday was drifting toward the summer season under the Julian calendar. The pope's fix, the Gregorian calendar, removed 10 days and tweaked the leap year formula. It's been keeping humans in time with the seasons pretty well ever since.

Despite this fix, there's still a very tiny fraction of a day unaccounted for each year. And those wee pieces of time will add up.

How much so? By the year 13000, our calendar will be out of sync with Earth's orbit by as much as the Julian calendar was under Pope Gregory, according to calculations calendar expert Charles Kluepfel did for Sky and Telescope magazine in 1982, the 400th anniversary of the pope's revision. The vernal equinox will have shifted backward 10 days, from around March 20 to March 10. Though our current calendar may have a best-by date, we have plenty of time — thousands of years — to come up with another tweak.