No. 167Time3 minviews 8
Published by GK Library Annex
Ipdong means winter, so why does it still feel like autumn?
A solar term set by the sun and a winter counted by temperature, weeks apart
Ipdong (입동), one of the 24 solar terms, falls on November 7 this year. Its name means “the start of winter,” but in Seoul, winter measured by temperature usually begins only around December 1. The gap exists because Ipdong is not set by measuring the weather. It is set by where the sun sits in the sky.
Ipdong is set by the sun’s position
The 24 solar terms are marks that divide the sun’s yearly path across the sky, as seen from Earth, into 15-degree steps. Counting the spring equinox as 0 degrees, Ipdong is the moment the sun reaches 225 degrees. This year that is 6:52 p.m. on November 7. Fifteen days earlier, October 23, was Sanggang (상강, “frost descent”), and fifteen days later, November 22, is Soseol (소설, “minor snow”).
So the date of Ipdong contains no information about that year’s weather. Whether the year is warm or cold, Ipdong arrives on almost the same day. The name says winter begins, but in practice it is closer to a calendar mark meaning “from here on, the year leans toward winter.”
When does the weather agency’s winter begin?
The Korea Meteorological Administration divides the seasons by temperature. It takes the daily mean temperature averaged over nine days and counts winter as starting on the first day that value drops below 5°C and does not climb back. Counted this way, Seoul’s winter began on December 1 on average for 1991 to 2020, more than three weeks after Ipdong.
The gap used to be smaller. On average for 1911 to 1940, Seoul’s winter began around November 18. As temperatures rose, the start of winter gradually moved later. On top of that, the solar term names were coined to fit the weather of the North China Plain long ago, so they never matched Korea’s weather exactly to begin with.
A common misconception: are solar terms lunar?
Many people think the solar terms belong to the lunar calendar, but because they are based on the sun, they actually line up well with the solar calendar. On the solar calendar, Ipdong is almost fixed on November 7 or 8 each year, while its date on the moon-based lunar calendar changes from year to year.
In daily life, it works well to treat Ipdong as the time to start preparing for winter. In the past, too, people made kimchi for the winter (gimjang, 김장) and got ready for the cold season around Ipdong. To decide when to bring out a heavy coat, the morning lows in the weather forecast are a more accurate guide than the solar term.
Ipdong follows the sun and comes around November 7 in any weather; Seoul’s winter by temperature starts in early December.
Notes and references · KASI 2026 calendar data; KMA seasonal normals. Ipdong time from KASI calendar data (released before the official almanac); Seoul’s winter start from KMA 1991–2020 normals. Actual dates vary by year and region.
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