Calendars and the beginnings of astronomy

Home > Opinion > Meanwhile

Calendars and the beginnings of astronomy

Published: 08 Jan. 2026, 00:05

Audio report: written by reporters, read by AI

Moon Hong-kyu

The author is a principal researcher at the Korea Astronomy and Space Science Institute.

Only a few days have passed since I opened a new calendar. The days yet to come are still wound tight, like a spring. Numbers burst open each date as if a cuckoo were leaping from a clock to announce the day. Everyone knows that a day is the time it takes the Earth to rotate once with respect to the sun, and a year is the time it takes to complete one orbit. The problem begins after that.

An employee makes calendars for 2026, the Year of the Fire Horse, at a calendar printing shop in Jangan District, Suwon, Gyeonggi Province, on Nov. 3, 2025. [NEWS1]

Multiply 365 days by 24 hours and it should come out neatly to 8,760 hours. Yet, like coffee grounds stuck to the bottom of a cup, there remains an extra 5 hours, 48 minutes and 45.2 seconds in a year around the sun. That is why Feb. 29 is added and removed every four years.

Perhaps my eyesight has worsened again. I squint, glasses perched on the tip of my nose, trying to make out the tiny lunar calendar numbers. A lunar month, from full moon to full moon or from new moon to new moon, averages 29 days, 12 hours, 44 minutes and 2.9 seconds. Once again, there is leftover change in a year, about 13 hours.

The moon travels along an elliptical orbit, sometimes pulling away to a distance that is three or four times Earth’s diameter farther than at its closest approach. As a result, each lunar month can vary by about seven hours from year to year. A supermoon is simply a full moon seen when the moon is closer to Earth.

What if a day, a month and a year fit together as precisely as interlocking gears, fixed at 24 hours, 30 days and 360 days, with the moon gliding elegantly along a perfect circle? Because of those remainders and that elliptical path, someone had to scrutinize the motions of the sun, moon and stars, grappling with calculations. Astronomy began that way.

Late last year, an overseas researcher visited the institute to present studies of exoplanets observed with the James Webb Space Telescope. The research captured signals of dimming light when so-called super-Earths and mini-Neptunes, with masses ranging from 1.2 to 9.6 times that of Earth, passed in front of their host stars.

Those worlds are heated to extremes, from temperatures comparable to grilling fish to conditions near molten lava. The likelihood of life there appears slim. Their years last anywhere from a day and a half to just 17 days as they skim close to their stars. Many are likely tidally locked, with their rotation period matching their orbital period so that a day and a year are the same.

In places where clocks and calendars coincide, life, too, might be correspondingly simple.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.