This study investigates the concept of fitting as a fundamental epistemic operation in Ptolemaic astronomy, following the methodological precept in Almagest IX.2, and its medieval Islamic reception, where newly observed empirical anomalies necessitated the construction of novel models through the adaptation of established hypotheses and model components. Situating Ptolemy’s fitting and typology of errors at the core of medieval astronomy’s evolution, the paper analyzes historical procedures for reconciling theoretical constructs with discrepant data. Central to this analysis are the models devised by Abū Jaʿfar al-Khāzin ( ca. 900– ca. 971) and Ibn al-Zarqālluh (d. 1100) to account for variations in precession, the obliquity of the ecliptic, and solar eccentricity. We introduce a core portion of al-Khāzin’s original account of his non-Ptolemaic physical ( hayʾa ) model and clarify its historiographical misinterpretation. We further reconstruct the rationale behind Ibn al-Zarqālluh’s fitting of his kinematic models to historical empirical data, detailing the necessary incorporation of a pivotal value for the solar eccentricity from pre-Islamic Persian astronomy.
The Shixian System ( Shixian li 時憲曆) of the Qing dynasty is a calendrical framework that integrated traditional Chinese mathematical astronomy with Western astronomy. From the eighteenth century onward, it was introduced into the Tibetan regions in two forms: One is the imperially composed Tibetan translation Rgya rtsis chen mo , the others, the Tibetan-compiled Ma yang rgya rtsis snying bsdus series. This study focuses on the solar eclipse algorithms found in these two series of texts, focusing on their textual sources, numerical tables, and astronomical models. The Rgya rtsis chen mo derives its eclipse algorithms from the Suan qizheng jiaoshi lingfan fa 算七政交食淩犯法. A comparison between the earliest and latest version in the Tibetan Shixian system shows that the eclipse limit values and solar motion tables are derived from the Yuzhi lixiang kaocheng houbian 御製曆象考成後編, while the remaining numerical tables are sourced from the Yuzhi lixiang kaocheng biao 御製曆象考成表. The main procedures and astronomical models are based on the Yuzhi lixiang kaocheng 御製曆象考成. Therefore, the Tibetan Shixian system represents an adaptation of the Yuzhi lixiang kaocheng series. This study employs Python programming to simulate the moments of solar eclipses for the period between 1744 and 1844, the average errors for three phases of solar eclipses are approximately 40 minutes, and the mean error in eclipse magnitude is 0.12.
This article examines a 3.5-foot transit instrument crafted by John Bird and used at the Stockholm Observatory in the late 18th and early 19th centuries. It argues that the instrument functioned not as an isolated precision device but as part of an interconnected operating chain comprising regulator clocks, calibration tools, architectural infrastructure and established observational routines. By tracing its acquisition, installation and daily use, the study shows how precision in meridian astronomy - particularly in time determination - was achieved through the continual stabilisation of a fragile and labour-intensive system.
This article discusses a hitherto unknown unsigned early European astrolabe kept at the Liceo Classico Alighieri in Ravenna. The astrolabe was made in Toulouse in 1216 and later seems to have been moved to Ravenna. Our investigations of the lettering, the design features, and the stars on the rete of the astrolabe show that the instrument was modelled on an Andalusian model dating to the last quarter of the 11th century.
This article uses a combination of biographical and situational factors, close textual analysis, and comparison with contemporaneous publications to illuminate the understudied formative phase of Soviet SETI (Search for Extraterrestrial Intelligence). I examine Iosif Shklovsky’s professional biography and the first Soviet SETI publication, his 1960 article, “Is Communication with Intelligent Beings of Other Planets Possible?” My research situates Shklovsky’s exploration of extraterrestrial intelligence within his broader scientific background and intellectual interests before offering a critical reconstruction of the article’s central arguments. It demonstrates how, through an examination of the evolution of matter in the Universe, Shklovsky framed intelligence and communication within a radio-astronomy-informed cosmology. Communication with other beings via electromagnetic radiation became integral to what SETI and astronomy historian Steven J. Dick later termed the “biological Universe.” I argue that the scientific characteristics Shklovsky articulated effectively naturalized the possibility of extraterrestrial radio communication. Last, I analyze this process of naturalization in the early 1960s Soviet SETI.
The Magliabechiana collection of the National Central Library in Florence preserves a copy of the Almagest , printed in Basel in 1551, that is densely annotated (BNCF, Magl. 5.1.133). The purpose of this article is to set out the full range of evidence—paleographical as well as textual and contextual—demonstrating that Galileo Galilei was the annotator. It is likely that the majority of the annotations were written by Galileo before he moved to Padua in 1592. An Appendix to the article includes a transcription and an English translation of an extensive annotation on Chapter 7 of Book V of the Almagest , illustrating the technical nature of the marginalia.
Since Clive Ruggles's "Whose Equinox?" (1997), the importance of the equinoxes in cultural astronomies has been robustly questioned, particularly in archaeological contexts. This study draws on the extensive ethnographic and linguistic evidence from the Hopi to examine the role of the solstices and equinoxes in a culture whose astronomy has a well demonstrated concern with the motions of the Sun. The striking contrast between the abundant evidence in the Hopi language that is related to the Sun and the solstices and the scarcity of such evidence related to the equinoxes illustrates the importance of the solstices in, what we can call the Hopi sunwatchers' "conceptual toolkit," providing a new perspective on an astronomy which is manifestly concerned with the Sun but demonstrates little concern with the equinoxes. The evidence reveals that the Hopi consciously used sequences of anticipatory observations to determine the days of the solstices, thereby establishing the framework of their cosmology and guiding further astronomical observations.
Many Mesoamerican hieroglyphic texts bear dates in indigenous calendars. Hundreds include dates in a lunation: the most ancient, in Zapotec texts, were observational; the most numerous, in Mayan texts, in a formal lunar calendar. Many Mayan lunar dates were projections into the past or future. Previous research has suggested evidence for specific computing ratios of days to months for such projections; that of 11,960 days to 405 lunations has long been accepted as the quintessential Mayan model for such calculations. This paper addresses observational evidence available to Mesoamerican calendar specialists for developing such models. It uses Lowry's corpus of lunar first appearances at Monte Alban (650 to 0 BCE) to determine which sequences would have stood out as most reliable observationally, shows that a ratio of 1447 days to 49 months would have been by far the most reliable, and provides circumstantial evidence for its use in Mayan calendrics.
Luminous blue variables (LBVs) are extremely massive, evolved stars that can experience highly erratic instabilities and outbursts. During an eruption, they are capable of temporarily being the brightest star in their host galaxy. By careful examination of two drawings of Messier 33 (M33) made in 1850-1851 and 1857, the currently well-known LBVs Variable B and Variable 83 have been found. The drawings show that Variable 83 was visible on both while Variable B had faded below detection on the second. Comparing the limiting magnitude of the stars plotted on the earlier drawing indicates that Variable B was near the brightest it has ever been measured at while Variable 83 was experiencing a brighter eruption than has since been recorded. These are the first known recorded observations of an LBV in any galaxy beyond the Milky Way.
The aim is to document the last 35 years of meridian circles, a type of instrument with a fundamental role in astronomy for a very long time, and to do so while witnesses are still alive and can contribute. Meridian circles provided fundamental star positions for centuries. These positions were tied to a well-defined celestial coordinate system of right ascension and declination, and accurate proper motions ensured the transformation of the positions over long periods of time. This function of the meridian circles has been taken over by space astrometry and VLBI, Very Long Baseline Interferometry. The Hipparcos astrometric satellite was approved by ESA, the European Space Agency, in 1980 and launched to a successful 3-year mission in 1989. Its successor, Gaia, completed a mission of 10.5 years in January 2025. An account is given of the last 18 meridian instruments, which were active for some part of the 35 years between 1980 and 2015. This account was made possible by input kindly supplied in correspondence with many colleagues.
