Analysis of Manchuria astronomical almanacs of 1933–1945

We investigate the astronomical almanacs of the Manchukuo state, which lasted for 14 years, from 1932 to 1945. We examine their contents and analyze the accuracy of the time data by using the almanacs for the years from 1933 to 1945. We find that the calendar of the Qing dynasty in China, Shixianshu, provided the name of the almanac. In addition, the reference location of the time data was Xinjing (now known as Changchun) and the standard meridian was changed from 120 ^∘E to 135 ^∘E , starting with the almanac of 1937. We also find that sunrise and sunset times were recorded only on days of the 24 solar terms, for several cities, whereas moonrise and moonset times were recorded daily, but only for Xinjing. Moreover, only days were recorded (i.e., the hours are not recorded) in the almanacs of 1933 and 1934 for the 24 solar terms. To estimate the accuracy, we first extract 19 kinds of time data and classify them into four groups: rising and setting, solar term, phases of the Moon and eclipses. Then, we determine the mean absolute difference (MAD) of the time data between the almanacs and modern calculations performed using the DE405 ephemeris. Even though most of the time data are recorded in minutes, we compute the data in seconds. We find that the MAD values are 0.44, 0.42, 0.27 and 0.44 min for the time data of the four respective groups. We believe that our findings will contribute to the study of the astronomical almanacs of Korea, Japan and Taiwan, which were published during this period.