In this biography
Quick facts
- Born
- 1874
- Died
- 1943
- Birthplace
- Sendai, Japan
- Country
- Japan
- Nationality
- Not independently established
- Known for
- Identifying asteroid families from related orbital quantities
Why this life matters
His work made the choice of orbital quantities central to recognising candidate families.
Timeline
Key moments
Positional astronomy
Works on measurements and changes of astronomical position.
Research in the United States
Works with E. W. Brown and develops an interest in asteroid research.
Asteroid groups
Publishes evidence for groups probably sharing an origin.
Position and motion before the asteroid families
Hirayama was born in Sendai and studied astronomy at Tokyo Imperial University. He worked in positional astronomy, where the precision of a measured direction matters as much as the object being measured. His career also included fieldwork connected with surveying on Sakhalin. These were problems in turning repeated measurements into a stable description of location.
During a period in the United States he worked with Ernest William Brown on lunar theory. The Astronomical Society of Japan’s account associates Brown’s encouragement with Hirayama’s move into asteroid research. The new problem also involved extracting an enduring pattern from quantities that vary.
Sources for this section: [1]
Looking for a group in changing orbits
Asteroid orbits are perturbed by other bodies. The orbital shape and tilt reported for one epoch need not remain the same. Hirayama considered quantities that were less affected by the oscillations he was modelling. In 1918 he reported groups that emerged when related orbital properties were compared. The groups suggested that some asteroids might share an origin.
The inference depended on how the comparison was constructed. Objects that happen to look similar in one snapshot do not necessarily remain together when the time variation is taken into account.
An observational pattern and an explanation
The title of the 1918 paper presents a probable common origin. It is useful to retain that level of claim. The orbital pattern identifies a candidate family, while explaining its formation needs additional evidence. The University of Tokyo exhibition places the first report in a longer history of family identification, in which later researchers found more groups using expanded records and methods.
Quick answers
Frequently asked questions about Kiyotsugu Hirayama
- What was a Hirayama family?
- It was a group of asteroids identified by similarities in orbital quantities after allowing for the variations considered in the analysis.
Keep exploring
Lives connected to this story
- Yoshihide Kozai
Compare a later Japanese treatment of changes in one inclined asteroid orbit.
- Carlyle Beals
Compare another case where a visible grouping became a hypothesis to test.
Sources and further reading
Explore the evidence
These references support the biography and offer further reading. Official records, first-person accounts and independent reporting provide different perspectives; image records document attribution and licensing.
- 1. Astronomical Society of Japan, Astronomy DictionaryKiyotsugu Hirayama
- 2. Kiyotsugu Hirayama, The Astronomical Journal 1918Groups of Asteroids Probably of Common Origin
Read the opening argument and comparison of orbital quantities. The worksheet is an abstraction and does not copy the paper’s orbital table.
- 3. University of Tokyo Library exhibitionProgress of Japanese Astronomy: Asteroids
