Tycho Brahe, Abu Mashar, and the comet beyond Venus (ninth century A.D.)

TL;DR

This paper explores the historical observations of comets by Abu Mashar and Tycho Brahe, analyzing their conclusions about celestial objects beyond Earth, and clarifies the scientific understanding and misconceptions of the time.

Contribution

It provides a new translation and interpretation of Abu Mashar's original Arabic text, revealing his reasoning about comets beyond Venus and its influence on Tycho Brahe's conclusions.

Findings

Abu Mashar observed Venus in comet tails and concluded comets were beyond Venus.

Parts of Abu Mashar's reasoning about comets outside Earth's atmosphere are correct.

The paper clarifies historical misconceptions about comet observations in the ninth century.

Abstract

From his observations of the A.D. 1572 super-nova and the A.D. 1577 comet, Tycho Brahe concluded that such transient celestial objects are outside the Earth's atmosphere, and he quoted the 9th century A.D. Persian astrologer and astronomer Abu Mashar: Dixit Albumasar, Cometa supra Venerem visus fuit, i.e. that he had reported much earlier that comets were seen beyond Venus. However, even from a more detailed Latin translation, the observations and logic behind Abu Mashar's conclusion were not understandable. We present here the original Arabic text (MS Ankara, Saib 199) together with our translation and interpretation: Abu Mashar reported that he had observed Venus in (or projected onto) the tail of a comet and concluded that the comet was behind Venus, because he had observed the extinction of Venus due to the cometary tail to be negligible (light of Venus was unimpaired). He then concluded that the comet would be located behind Venus. He also mentioned that others had observed Jupiter and Saturn in cometary tails, so that those comets would even be located beyond those two outer planets - in the sphere of the stars. The dates of the observed close conjunctions were not mentioned; using known orbital elements for a few comets, we found a few close conjunctions between comets and planets from A.D. 770 to 868, but we cannot be sure regarding which conjunctions were reported. While the argument of Abu Mashar is not correct (as cometary tails are optically thin), parts of the conclusion - namely that comets are outside the Earth atmosphere and beyond the moon - is correct. This may have helped Tycho Brahe to come to his revolutionary conclusion.