30. Fireball radiants of the 1st–15th centuries

Abstract

The works of E. Biot, published by the Institut National de France in 1848, made it possible to study material recorded in volumes 191 and 192 of the well-known 13th-century Encyclopaedia of Ma Touan-lin as well as records from other sources. They contain observational data of 24 centuries (especially from the 11th century) on more than 1500 fireballs, with descriptions of their positions with respect to the stars as well as descriptions of their physical, kinematic and other properties. The observation dates of the lunar calendar have been converted by Biot into dates of the Julian Calendar.We have been able to process data on 1220 fireballs. As a result of this radiants were obtained for 153 meteor showers, seven of which belong to great showers. Out of the remaining 146 radiants of the minor showers, 80 radiants are more certain than the remainder.The radiants were deduced from observations on dates recorded in short intervals from several years to several decades. First the dates of visibility were obtained along with the activity and radiants of great showers which are still active. In the Leonid shower, with retrograde motion, a shift of visibility dates to a much later period has been noted corresponding to a forward motion of the orbit's node, whereas a retrograde motion of the node is observed in the Quadrantids (i < 90°). In the Lyrids and Perseids, whose orbits are nearly perpendicular to the ecliptic plane, the nodes experienced no perturbations, and the visibility epochs for the showers remained the same during a period of 1000 years and longer. The motion of apsides resulted in a shift of the radiant; the increase of the ecliptical latitude indicated secular augmentation of the orbit's inclination (Geminids, η-Aquarids, Orionids, Leonids). The radiant of the Perseids was located in Cassiopeia, where the radiant of the present-day Cassiopeids is to be found. It appears that the Perseid stream began to cross the orbit of the Earth in 830 A.D.In the δ-Aquarids the North branch was active, while there is no evidence that the South branch had existed earlier than 900 years ago. The Virginids, Librids, Scorpionids, Sagittarids and Aurigids were quite appreciable and their studies furnish much interesting data. Particularly active were the Taurids; their North and South branches were observed over 1000 years back. The South Taurids were about half as active as the North Taurids (at present this relation is reversed). Very active were the Cygnids (July–August), which presented at that time a compact shower, now disrupted into a series of minor showers with radiants spread over a large area of the celestial sphere. Of definitive interest is the radiant of the great meteor shower observed in 1037 (August 21 by the Julian Calendar, September 9 by the Gregorian Calendar, 1950–0), α = 324°, δ = + 1°(1950–0).Some of the showers active in these early centuries are now unknown; on the other hand, some showers which are well known now were not observed in the Middle Ages. In the past millennium only those streams have survived whose orbits were so situated with respect to the orbits of the outer planets, that they were not subjected to any considerable perturbations produced by these planets.