Although the heat lingers in the midday, the shade of the trees grows darker, and the sky stretches higher and bluer. Cool winds blow in the mornings and evenings, and during an early dawn walk, dew sparkles brightly on the grass. Surprised by the beauty, I take a closer look around to see late-blooming flowers, vibrant green leaves, and dew on the grass, all shining like jewels. The beauty is striking. Oh, even while we've been indifferent, nature has existed in such splendor! Indeed, even the Bible speaks of how Solomon's glory cannot compare to the glory of a simple flower.

  And now, today is Baekro (白露), a term meaning "white dew," indicating that dew forms on grass or objects as the night time temperatures drop. Despite the lingering heat, dew still falls, and the seasons continue to change, making me realize how peculiar the seasonal divisions really are.

  In reality, our lives are closely connected with these seasonal divisions, and we often gauge the flow of the seasons through them. We say things like, "Since Cheoseo (處暑) has passed, the heat will soon retreat — haven't you heard that even mosquitoes' mouths start to twist?" This is because 'Cheo means 'place, time, stay,' and 'Seo' means 'heat,' so Cheoseo indicates a time when the heat no longer lingers. Hence, such sayings feel natural.

  But how is it that Malbok (末伏, LITERALLY, LAST HOTTEST SUMMER DAY) comes after Ipchu (立秋, FORMAL BEGINNING OF AUTUMN)? This year, Ipchu was on August 7th, and Malbok was on August 14th. Both are terms for the seasonal divisions, so it raises questions. How can a summer term come after an autumn term? It seems like a misallocation of seasonal divisions.

  At this point, it's worth investigating further. Ipchu and Malbok are Chinese characters, so could they be based on the lunar calendar? After all, Korea has historically used the lunar calendar for agricultural purposes, so this theory seems plausible.

  However, to jump to a conclusion would be wrong. Given that this has come up, let me break this down step by step. 

  First, seasonal divisions like Ipchu and Baekro are based on the solar calendar. That is, it is a kind of calendar created to divide the year into seasonal sections based on the sun’s path across the sky. The path the sun travels is known as the ecliptic, and the seasonal divisions divide this path into 24 sections, each spaced 15 degrees apart starting from the spring equinox. Astronomers believed that every 15-degree movement of the sun brought a change in temperature or season. They assigned appropriate names to these points, which became the seasonal divisions. Of the 24 divisions, some like Chunbun (Spring Equinox), Chubun (Autumn Equinox), Haji (Summer Solstice), and Dongji (Winter Solstice) mark changes in seasons, while others like Soseo, Daeseo, Cheoseo, and Daehan refer to heat and cold. Terms like Baekro, Hanro, and Sanggang refer to the condensation of water vapor, dew, and frost.

  However, the "three hottest days" of summer (Sam-bok 三伏) are not part of the seasonal divisions mentioned above. The first Gyeong-il (庚日) after the summer solstice is called Chobok (the first hottest day), followed by Jungbok (the second hottest 中伏), and finally Malbok (the last hottest). Gyeong-il refers to one of the ten heavenly stems in the sexagenary cycle, where the seventh day is called Gyeong. Jungbok comes 10 days after Chobok, and Malbok is 30 days after Chobok. That’s why Malbok comes after Ipchu, a term for autumn in the seasonal divisions. During this period, the persistent heat often leaves both body and spirit exhausted. Our ancestors wisely created Boknal (the three hottest days) as a way to endure the heat, traditionally eating nourishing foods to regain strength.

  In this context, it becomes clear that Korea has historically used a lunisolar calendar, combining both the lunar calendar and the solar calendar to complement each other. They measured days based on the moon's phases and determined the seasons according to the sun’s movement.

  The lunar calendar, which focuses on the moon’s phases, was primarily used to create daily and monthly calendars without considering the seasonal changes brought by the sun. This system, also called the Islamic Hijri calendar or pure lunar calendar, was introduced to Korea through China and organized during the reign of King Sejong. While the sun’s altitude changes only yearly and was difficult to measure with the astronomical knowledge of the time, the moon's phases change daily and are easier to track. Measuring the moon's phases also helped in industries like fishing, navigation, and astronomy, which rely on the moon's gravitational pull. However, because farming is closely related to the sun’s movement, the solar terms for seasonal divisions were used to complement the lunar calendar. Thus, the lunar calendar was not very helpful for farming.

  The solar calendar, on the other hand, was developed in ancient Egypt through the study of the connection between the flooding of the Nile and the position of the sun. Later, Western societies adopted the solar calendar, while Egypt now uses the lunar calendar. In Korea, the solar calendar was officially adopted during the reign of King Gojong in 1896, thanks to the efforts of the reformist faction at that time, who wanted to embrace Western systems.

  As the saying goes, the more you know, the more you see. Looking around during the Baekro, the dew seems to sparkle even more brightly. Though the midday heat still lingers, I’m confident and comforted, knowing that Cheoseo has passed and today is Baekro. How much longer can this heat hold on? Also, the cicadas that buzzed loudly all summer have quieted down, and now the sound of crickets is growing stronger.