stations. Twelve pairs of stars were selected and observed continuously at these
stations. The results of the variation in latitude were plotted on the two-dimensional
(x, y) plane of the position of the Earth’s pole. In 1902, Kimura found that the
variations should be traced in three-dimensional space and added a new z-term as
follows:
Δφ ¼ x cos λ þ y sin λ þ z
ð2:1Þ
where Δφ indicates the latitude variation; x, y, and z denote the position of the
Earth’s pole; and λ denotes the west longitude of each observatory (Kimura 1902).
The path of the (x, y) position and the mean curve of the z-term are illustrated in
Fig. 2.4. The amplitude of x, y variations was around 0.17 arcsec, which corresponds
to around 5 m of pole displacement. The existence of the z-term indicates that the
Earth could not be a solid body. It is now thought that the z-term is due to the
presence of a liquid core deep in the Earth’s interior, though there remain problems
to be studied to understand its real origin.
For this discovery he won the Gold Medal of the Royal Astronomical Society in
1936, and the Order of Culture (文化勲章) from the Japanese government in 1937.
He died in Tokyo at age 73.
2.2.4 Hirayama Shin and Astronomy
Hirayama Shin (平山信, 1868–1945) worked on positional astronomy in the Meiji
era and on astrophysics from Taisho to the early Showa era (1918–1932) (Hagihara
1947).
Fig. 2.3 Photograph of
Kimura Hisashi with the
Order of Culture
(文化勲章) in 1937
(Hashimoto 1943)
20
2 Astronomy from Meiji to Taisho Period 1868–1926