Bi-Daily Venus (BDV) is an uncommon event, occurring when an observer can view that planet twice in a single day – in the twilight of dawn and dusk. That William of Conches knew of this phenomenon in twelfth-century France is surprising given the dearth of BDV accounts. Yet following unnamed sources, he discussed BDV in three of his works: Philosophia Mundi, Glosae Super Boetium, and Dragmaticon. From

In 1939, the British Admiralty agreed to move the Royal Observatory from Greenwich to a better site away from London. The removal was postponed due to the Second World War, and the observatory’s re-establishment at Herstmonceux Castle in Sussex in the 1940s and 1950s was further delayed by post-war economic difficulties. This paper examines several proposals to remove the observatory that were put

The observatory of Ulugh Beg, erected in Samarqand in the 1420s, represents the culmination in the development of astronomical observatories in the Islamic world. After its rediscovery and excavation in the early twentieth century there have been several attempts to reconstruct its appearance and explain how it worked in detail, based on archaeological finds and the analysis of relevant manuscripts

The State Archives of Belgium, in particular, the archives of Archduke Albert VII of Austria, hold a letter which possibly is a copy of the letter, or an excerpt of the letter, of Kepler to Emperor Rudolf II of October 1604 on SN1604, that is, the first letter of Kepler on the subject. Together with this letter, there are other letters on SN1604, written by Johannes Brengger and Michiel Coignet. In

Drawing on the results of his experiments with vacuum, Otto von Guericke put forward his own theory of comets. He explained this theory in his letters to Stanisław Lubieniecki who later published Guericke’s and his own letters in his Theatrum cometicum (1666–1668). Guericke also wrote about comets in his Experimenta nova (1672), simply reprinting the correspondence from Lubieniecki’s book. All subsequent

After the discovery of the new star of 1572, we find similar phenomena enumerated in the contemporary literature. The earliest of such lists, like that of Riccioli, looked like the cometary historiae of the time. They listed various kinds of objects, which could be put into three classes: mythological, astronomical, and astrological. These compilations were usually gathered from a perusal of the literature

One hundred years ago, J.K. Fotheringham famously derived the “accelerations” of the Sun and Moon from the reports of 11 classical solar eclipses. We review critically the reliability of these eclipse reports and rework his diagrammatic method, treating the deceleration of the Earth’s rotation as an unknown, rather than the “acceleration” of the Sun. There is some serendipity in his choice of the critical

The first determination of the surface temperature of stars other than the Sun is due to the Hungarian astrophysicist Béla Harkányi. Prompted by the recent unprecedented increase in the availability of stellar temperature estimates from Gaia, coinciding with the 150th anniversary of Harkányi’s birth, this article presents the life and work of this neglected, yet remarkable figure in the context of

Historians of science have amply demonstrated the transnational character of science; however, they have not sufficiently attended to how several scientific projects were coordinated as part of global initiatives. Our research – based on the unpublished, written correspondence between Christian Ludwig Gerling in Germany and James M. Gilliss in the United States, from 1847 to 1856 – examines the issues

When at the beginning of 1600, Kepler arrived to work with Tycho Brahe, Longomontanus, Tycho’s principal assistant, who was working with a model for Mars that predicted with remarkable accuracy its longitudes at oppositions. According to Kepler, this hypothesis “represented all these oppositions within a distance of two minutes in longitude.” The model, however, was unsuccessful in predicting longitudes

The Liber theoreumacie is a neglected work of practical geometry, written in Strasbourg in 1214, which sheds valuable light on the study and practice of astronomy in early thirteenth-century Europe. In this article, I focus on the first two chapters of Book IV, which both deal with the construction of horary instruments. The first of these chapters contains the earliest known account of the type of

The reports of seven eclipses of the Sun and Moon in Bede’s Ecclesiastical History and its Continuation are investigated for their astronomical accuracy using modern-day calculations. The eclipses can all be identified from the given dates, which are accurate to within 2 days, except for one lunar eclipse. There is evidence that the reports were obtained from a range of sources beyond the NE of England

Between 1890 and 1895, five women “computers” were hired to work at the Royal Observatory, Greenwich, one of the world’s leading observatories at the time. Caroline Herschel notwithstanding, these women were the very first in Britain to be paid for astronomical observation. They were hired as supernumerary computers – normally a temporary position reserved for young schoolboys. Instead of adhering

This article offers new insights into a series of dramatic events that took place at the imperial Chinese court in December 1668, in which astronomy, politics, and religion all played major roles. Jesuit missionaries had served the Manchu rulers of the Qing 清dynasty as official astronomers since the dynasty seized Beijing in 1644. But in autumn 1664, the Jesuits at court were imprisoned as a result

Ptolemy explicitly claims in the Almagest to have made 36 observations. For most of them, the date of the observation is determined by the kind of phenomenon observed, for example, the observation of a lunar eclipse or of an equinox. There are six observations, however, in which a particular date is not required by the nature of the phenomenon under investigation. In five of them, Ptolemy measures

Isaac ben Solomon Ibn al-Ḥadib (or al-Aḥdab) emigrated from Castile to Sicily no later than 1396. In astronomy, his most important work, written in Hebrew, is The paved way (Oraḥ selula), a set of tables for the motions of the Sun and the Moon. Here, we focus attention on his unusual tables for finding the difference in time and the difference in longitude between mean and true syzygy, where syzygy

The comet 27 P/Crommelin was discovered in 1457 and since then observed six times up to 1956, so its average period is 27.79 years. According to Korean ancient annals, however, comet 27 P/Crommelin was first observed in B.C. 44 and was observed 16 times up to 1457. We traced the records with a period of about 28 years, compiled a list of them and showed that all those records are concerned with the

In 1717, Halley compared contemporaneous measurements of the latitudes of four stars with earlier measurements by ancient Greek astronomers and by Brahe, and from the differences concluded that these four stars showed proper motion. An analysis with modern methods shows that the data used by Halley do not contain significant evidence for proper motion. What Halley found are the measurement errors of

This article introduces various definitions and criteria for the astronomical phenomena of “encroachments” (close lunar and planetary conjunctions) in pre-modern China. With improvements in observations and mathematical astronomy, the standard of encroachments began to undergo many changes leading to more precise explanations of the phenomena. Before the adoption of Huihui Lifa (Islamic-Chinese calendrical

It is often claimed that the 1676 discoveries at the Paris Observatory of a new irregularity in the orbit of Jupiter’s first satellite and of the velocity of light were not due to Rømer alone but that Cassini played a major role or even that Rømer took over these ideas from Cassini. These claims indirectly accuse Rømer and Cassini of dishonesty. We investigate the foundations of these allegations through