185 Chinese Observe “Guest Star”

Ancient Chinese astronomers were meticulous observers of the skies. As historians have pointed out, because official Chinese astronomy research was often conducted by cadres of full-time, court-appointed civil servants as opposed to individual scholars, they were much more systematic and thorough about surveying the skies for changes than their Roman, Greek, or Babylonian counterparts and predecessors were. Thus, when something new happened in the sky, the Chinese noticed and recorded the observation, and the recording became part of the imperial dynastic records, many of which are still preserved.

A prime example was the sudden appearance of what they called a guest star in the southern skies in the year 185. This appearance was recorded by Chinese astronomers as a notable event in the surviving annals of the Eastern Han dynasty (25–220 CE). Although no drawings were included, the description of the location of the guest star and the fact that it faded from view over a period of about six months convinced modern astronomers that the Chinese had made the first recorded observations of a supernova. Modern optical, radio, and X-ray telescopes trained on that location reveal a semispherical gaseous nebula called RCW 86, which appears to be the expanded remains of that stellar explosion from more than 1,800 years ago.

A modern view of the remains of the supernova explosion of 185.

Many other guest stars were recorded in ancient Chinese astronomical drawings that are still preserved today. Among the most interesting are drawings that show objects with a bright, round “head” and one or more feathery or spiky “tails.” These objects were referred to as “broom stars” by the Chinese, and they are now widely interpreted as bright comets with long tails of gas and dust. In fact, prominent comets observed by Chinese astronomers in 240 BCE and 12 BCE, and in 141, 684, and 837 CE, are all likely to have been observations of the same comet, eventually recognized in 1682 as the 76-year periodic Halley’s Comet. The careful, methodical sky watching and record keeping of early Chinese astronomers has proven to be a rich treasure trove of data for studies by both historians and astronomers.

Ancient Chinese drawings of the changing appearances of several comets, as recorded in the Bamboo Annals, a historical accounting of China covering the period from about 2400 BCE to 300 BCE.