Sambok (三伏, Three Hottest Days) is the common designation of Chobok (初伏, Early Hot Day), Jungbok (中伏, Middle Hot Day), and Malbok (末伏, Late Hot Day), and widely known to be one of the Korean folk customs. Hence, Sambok is notated in Manseryeok (Ten Thousand-Year Almanac) and in the annual astronomical almanac published by Korea Astronomy and Space Science Institute. In this paper, we investigate the changes of Sambok in Korea based on various documents such as Joseonwangjosilok (朝鮮 王朝實錄, Annals of the Joseon Dynasty), Jeungbo-Jakryeoksik (增補作曆式, The Supplement of Manual for Calendar Making), astronomical almanacs, and so forth. According to Jeungbo-Jakryeoksik preserved in Kyujanggak Institute for Korean Studies, Chobok and Jungbok are defined as the third and fourth Gyeongil (庚日, The Day Starting with the Seventh Heavenly Stems in Sexagenary Cycles Assigned to Each Day) after the summer solstice, respectively, and Malbok is the first Gyeongil after Ipchu (Enthronement of Autumn). However, if the summer solstice is Gyeongil, then the third Gyeongil counting from the solstice becomes Chobok. Malbok depends on the time of Ipchu. Ipchu itself becomes Malbok if the time of Ipchu is in the morning, or next Gyeongil becomes Malbok if it is the afternoon. On the other hand, Malbok is defined as Ipchu itself regardless of its time according to Chiljeongbobeob (七政步法, Calculating Method for Sun, Moon, and Five Planets), Chubocheobryeo (推步捷例, Quick Examples for Calendrical Calculations), and so on. To verify the methods used to determine Sambok, we examined the record in the extant almanacs during the period of 1392 to 2100 for which the summer solstice or Ipchu is Gyeongil. As a result, we found a periodicity that if the time of Ipchu is in the morning, in general, the time is in the afternoon after two years and then is back into in the morning after nineteen years, i.e., the 2 + 19 years periodicity. However, we found the 2 + 17 years periodicity in some years. We also found that the Chobok method of Jeungbo-Jakryeoksik has been used since 1712, the thirty-eighth reign of King Sukjong (肅宗). In addition, we supposed that Malbok had been determined by the method like Chubocheobryeo since either 1846, the twelfth reign of King Heonjong (憲宗), or 1867, the fourth reign of King Gojong (高宗). At present, these methods of Sambok are customarily used without any legal basis. We, therefore, think that this study will help conventionalize the method defining Sambok in the future.

ABSTRACT
1. 서론
2. 실록에 기록된 삼복 기사
    2.1.『세조실록』
    2.2.『영조실록』
3. 『작력식(作曆式)』에 기록된 삼복 기사
    3.1. (규)증보작력식
    3.2. (도)증보작력식
    3.3. (규)작력식, (칠)작력식, (추)작력식
    3.4. 삼복 결정법의 변천내용
4. 삼복의 변천과정 검증
    4.1. 초복의 변천
    4.2. 말복의 변천
5. 토의
    5.1. 간행연대
    5.2. 월복률
6. 결론
REFERENCES

• 민병희(한국천문연구원/충북대학교 천문우주학과) | BYEONG-HEE MIHN (Korea Astronomy and Space Science Institute/Chungbuk National University)
• 이기원(대구가톨릭대학교 기초교양교육원) | KI-WON LEE (Catholic University of Daegu)
• 안영숙(한국천문연구원) | YOUNG SOOK AHN (Korea Astronomy and Space Science Institute)
• 안상현(한국천문연구원) | SANG-HYEON AHN (Korea Astronomy and Space Science Institute)
• 이용삼(충북대학교 천문우주학과) | YONG SAM LEE (Chungbuk National University)