The Crab Reappears
In 1731, English astronomer John Bevis turned his telescope to the same patch of sky in Taurus, and revealed an object that came to be known as the Crab Nebula. In 1758, Charles Messier initially mistook the same blurred object in his eyepiece for Halley’s Comet, one of the reasons he created his now-famous list of Objects That Are Not Comets, frustrated by all the stationary blurs scattered across the heavens.
Messier’s list is now one of the most famous catalogs of celestial objects, and is frequently utilized by amateur astronomers. The catalog makes up some of the brightest and most beautiful telescope targets in the sky, and the Crab Nebula is memorialized as Messier Object Number 1. Astronomers across 200 more years viewed the nebula’s fine tendrils and blobby shape, drawing pictures and taking photographs that, in typical astronomy fashion, rarely resembled any kind of crustacean.
In 1921, Carl Otto Lampland observed changes in the nebula’s shape. These changes are nothing Lampland could have observed by himself. Instead, he was comparing his observations to those taken across the past two centuries by other astronomers. Yes, many of these observations were from hand-made drawings but nonetheless a consistent story appeared: The nebula was growing.
Expanding Nebula
What’s more, they could measure the speed of the expansion, and count backwards. They calculated that the nebula had been expanding for something like 900 years. Astronomers combed the records, turning up the record of the Chinese guest star, and then the matching Japanese account. Astronomers realized this evolving cloud of gas occupied the exact location described in records from almost a millennium prior. Thanks to other recent advances in the understanding of stellar evolution, they realized the nebula, until recently a catch-all term for any cloudy object in the heavens, was in fact a
supernova remnant: the last vestiges of a star’s spectacular and explosive demise.
If it were a supernova, it would have been readily visible to long-ago astronomers, or even to Joe the Farmer and Non-Astronomer standing outside his house at night. Once they began looking, other possible matches arose in the Middle East, Europe, and even the Americas, though many of these are ambiguous or disagree on specifics of date and location.
