The Korea Astronomy and Space Science Institute said on the 22nd that the harvest moon will rise at 5:34 p.m. on September 25, this year's Chuseok, as seen from Seoul, and will stand highest at 11:31 that night.

By region, moonrise comes earliest in Ulsan at 5:24 p.m., followed by Busan at 5:25, Daegu at 5:27, Daejeon at 5:32, Sejong at 5:33, Gwangju at 5:34 and Incheon at 5:35, all measured at sea level.

The moon seen on Chuseok night is not perfectly round; a sliver on its left remains unfilled. The moment it sits directly opposite the sun, making it truly full, is 1:49 a.m. on September 27.

Why the Fifteenth and the Full Moon Diverge

The gap between the fifteenth day of the lunar month and the true moment of fullness arises because the moon's orbit is an ellipse rather than a circle. It moves faster when nearer the Earth and slower when farther, so a difference of about a day opens between the reference time for the first of the month and the actual moment of fullness.

To the naked eye the difference is hard to see. For roughly two days on either side the moon looks the same round shape. Between astronomy's exact hour and the moon people feel on a holiday there is always a little slack.

One Moon, Three Places, One Festival

Chuseok and the Mid-Autumn Festival fall on the same day of the lunar calendar. In Korea, China, Taiwan and the many countries where Chinese communities are scattered, people look at the same moon on the same night. The foods differ, from songpyeon and mooncakes to taro soup and pomelo, but the hour of looking up overlaps.

In Chinese households in Korea it is common for both holidays' foods to share a table. Chinese restaurants and bakeries in Incheon and Seoul see more customers looking for mooncakes around this time, and school and association events cluster in the same week.