It is proved by old records on many particular astronomical phenomena in the periods of Koguryo (277 B.C. - 668 A.D.), Koryo, the first unified state in Korea and Ri Dynasty.

The Korean nation calculated a year as 365.25 days already at the beginning of Koguryo and as 365.246 days from around the 4th century.

They saw a month as 29.530 days.

There remain in the data belonging to Koguryo 11 records on solar eclipse, 10 records on comet, 5 records on meteor fall, 4 records on planet and 1 record on the observation of the sun.

The record on comet made in November of the year of 46, nearly 2,000 years ago, is the oldest observation one in Korea. It is a priceless historical record which cannot be found in foreign countries in those days.

While meticulously observing astronomical phenomena including solar eclipse, the Koguryo people discovered large maculae on the surface of the sun in September of the year of 640 and left a record on it.

Many records on observation of astronomical phenomena written in the periods of Koryo and Ri Dynasty remain still.