arXiv subjects

Koji Murata

Publications and source records attributed to Koji Murata.

3 recordsLinked to original sources

arXiv2026

Analyses on Christoph Clavius' Reports of Total Solar Eclipses in 1560 and 1567: Key References for the Centennial Variations of the Earth's Rotation Speed and the Solar Radius

Variations in solar radius (hereafter R_Sun) is a key reference for solar magnetic activity in time. The sunlight amount may have varied with R_Sun and had an effect on the Earth's climate in the past. Eclipse observations offer a unique opportunity to measure the absolute R_Sun value before modern direct observations. The scientific community has discussed a possible long-term R_Sun variability from 1715 onward. Prior to their coverage, Clavius' eclipse reports had been subjected to qualitative debates regarding the local eclipse visibility and a possible secular R_Sun trend. This study leverages the recent dramatic developments of lunar topography data and ephemeris data to provide an effective resolution of this debate. Clavius' eclipse reports described an explicit totality in 1560 at Coimbra and a "slender circle" around the eclipsing Moon in 1567 at Rome. Our study revised the ΔT constraints of -492 s =< ΔT =< 200 s in 1560 and 140 s =< ΔT =< 151 s in 1567 to satisfy Clavius' descriptions, considering the lunar limb profile and assuming Auwers' canonical R_Sun. This study constrains the R_Sun margin of 1567, utilising three scenarios to interpret Clavius' account. The local totality requires an upper R_Sun limit of 1567 as R_Sun =< 696200 km in absolute size (959.92" in angular size), indicating no linear secular R_Sun shrinkage but possible R_Sun oscillations on a centennial timescale. Conversely, the annularity scenario is considered unlikely because it requires an R_Sun decrease of 7.5" within 3 centuries, even beyond the capacity of extreme shrinking-Sun hypotheses.

astro-ph.SR↗

arXiv2021

Daniel Mögling's sunspot observations in 1626 - 1629: A manuscript reference for the solar activity before the Maunder Minimum

The sunspot groups have been observed since 1610 and their numbers have been used for evaluating the amplitude of solar activity. Daniel Mögling recorded his sunspot observations for more than 100 days in 1626 - 1629 and formed a significant dataset of sunspot records before the Maunder Minimum. Here, we have analysed his original manuscripts in the Universitäts- und Landesbibliothek Darmstadt (ULBD) to review Mögling's personal profile and observational instruments and derive number and positions of the sunspot groups. In his manuscript, we have identified 134 days with an exact sunspot group number and 3 days of additional descriptions. Our analyses have completely revised their observational dates and group number, added 19 days of hitherto overlooked observations, and removed 8 days of misinterpreted observations. We have also revisited sunspot observations of Schickard and Hortensius and revised their data. These results have been compared with the contemporary observations. Moreover, we have derived the sunspot positions from his sunspot drawings and located them at 2°-23° in the heliographic latitude in both solar hemispheres. Contextualised with contemporary observations, these results indicate their temporal migration to lower heliographic latitudes and emphasise its location in the declining phase of Solar Cycle -12 in the 1620s. His observations were probably conducted using a pinhole and camera obscura, which made Mögling likely underestimate the sunspot group number by >~ 33% - 52 %. This underestimation should be noted upon their comparison with the modern datasets.

astro-ph.SR↗

arXiv2020

Cometary records revise Eastern Mediterranean chronology around 1240 CE

Eirene Laskarina, empress of John III Batatzes of the exiled Byzantine Empire of Nicaea (1204--1261 CE), was an important Eastern Mediterranean figure in the first half of the thirteenth century. We reassess the date of Eirene's death, which has been variously dated between late 1239 and 1241, with the understanding that narrowing the range in which this event occurred contributes much to understanding the political situation in the area around 1240. George Akropolites, a famous official of the Empire, gives an account that connects Eirene's death to a comet that appeared "six months earlier", thus pointing to two comet candidates that were visible from the Eastern Mediterranean between 1239 and 1241, one recorded on "3 June 1239" and the other on "31 January 1240". Recent historians prefer the former, based on historical circumstances and without a critical assessment of the comet records. We revisit the historical records and reveal that the "3 June 1239" candidate was not a comet. On the other hand, the other candidate, sighted on "31 January 1240", was a comet, as supported by multiple historical records in multiple regions, and is also a good fit with Akropolites's narrative. Therefore, we conclude that Eirene died six months after the comet that was seen on 31 January 1240, which places her death in the summer of 1240. Given that the date of her death is crucial for determining some other contemporary events across the Eastern Mediterranean, our results offer a solid basis for further research on the thirteenth-century Eastern Mediterranean.

physics.hist-ph↗