Crab Nebula - Wikipedia

On April 22, 1056, the supernova Crab nebula was first seen by the naked eye. From the article:

"The Crab Nebula was first identified in 1731 by John Bevis.[15] The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet.[15] Messier catalogued it as the first entry in his catalogue of comet-like objects;[15] in 1757, Alexis Clairaut reexamined the calculations of Edmund Halley and predicted the return of Halley's Comet in late 1758. The exact time of the comet's return required the consideration of perturbations to its orbit caused by planets in the Solar System such as Jupiter, which Clairaut and his two colleagues Jérôme Lalande and Nicole-Reine Lepaute carried out more precisely than Halley, finding that the comet should appear in the constellation of Taurus. It is in searching in vain for the comet that Charles Messier found the Crab nebula, which he at first thought to be Halley's comet.[16] After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet. Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets.[16]

William Herschel observed the Crab Nebula numerous times between 1783 and 1809, but it is not known whether he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. After several observations, he concluded that it was composed of a group of stars.[17] The 3rd Earl of Rosse observed the nebula at Birr Castle in 1844 using a 36-inch (0.9 m) telescope, and referred to the object as the "Crab Nebula" because a drawing he made of it looked like a crab. He observed it again later, in 1848, using a 72-inch (1.8 m) telescope and could not confirm the supposed resemblance, but the name stuck nevertheless.[18][19]

In 1913, when Vesto Slipher registered his spectroscopy study of the sky, the Crab Nebula was again one of the first objects to be studied. In the early twentieth century, the analysis of early photographs of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900 years ago. Historical records revealed that a new star bright enough to be seen in the daytime had been recorded in the same part of the sky by Chinese astronomers in 1054.[17][20]

Changes in the cloud, suggesting its small extent, were discovered by Carl Lampland in 1921.[8] That same year, John Charles Duncan demonstrated that the remnant is expanding,[21] while Knut Lundmark noted its proximity to the guest star of 1054.[20][22]

In 1928, Edwin Hubble proposed associating the cloud to the star of 1054, an idea which remained controversial until the nature of supernovae was understood, and it was Nicholas Mayall who indicated that the star of 1054 was undoubtedly the supernova whose explosion produced the Crab Nebula. The search for historical supernovae started at that moment: seven other historical sightings have been found by comparing modern observations of supernova remnants with astronomical documents of past centuries. Given its great distance, the daytime "guest star" observed by the Chinese could only have been a supernova—a massive, exploding star, having exhausted its supply of energy from nuclear fusion and collapsed in on itself.

Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between apparent magnitude −7 and −4.5 (brighter than everything in the night sky except the Moon) by July. The supernova was visible to the naked eye for about two years after its first observation.[23] Thanks to the recorded observations of Far Eastern and Middle Eastern astronomers of 1054, Crab Nebula became the first astronomical object recognized as being connected to a supernova explosion.[17]"