The Crab Nebula Supernova 1054 AD
The Biggest July 4 Fireworks Explosion in History Formed M1
On July 4, 1054 the supernova that formed the Crab Nebula occurred in the constellation Taurus. It was bright enough to be visible in the daytime for nearly a month.
Supernovae
A supernova is a huge stellar explosion involving the entire star. The supernovae that mark the death throes of massive stars, Type II supernovae, play a crucial role in forming the atoms in our bodies. At their peak brightness, supernovae can outshine the entire galaxy containing them. They emit as much energy as the Sun does in its 10 billion year lifetime. Although they are common on cosmic time scales, supernovae in our own galaxy are rare on human time scales.
Crab Nebula
Observing the Crab Nebula requires a telescope and a dark moonless night. In a modest telescope it looks like a barely visible fuzzy patch near the naked eye star, Zeta Tauri. John Bevis, a British physician and amateur astronomer, first discovered it in 1731.
On September 12, 1758 Charles Messier independently rediscovered the Crab Nebula. As the first object in Messier's famous catalog, it is also known as M1. It is among the most studied objects in the sky.
In 1913, C. O. Lampland, working at Lowell observatory, started a long term program to look for changes in the structure of various nebulae. Lampland took several high quality pictures each year of the nebulae in the study. After eight years, Lampland struck gold on the Crab Nebula. Comparing the 1913, 1915, and 1916 negatives to the 1921 negative Lampland noticed changes hinting that some structure may be moving away from the central star. A star forming nebula, such as the Orion Nebula, should be collapsing rather than expanding. Hence the Crab Nebula is the still expanding remnant of a stellar explosion - a stellar burial shroud rather than a stellar nursery. From its current size and expansion rate we can compute that the explosion that formed the Crab took place occurred during the 11th century.
Chinese Observations
Ancient Chinese recorded a more accurate date. Their highly developed civilization kept written astronomical records dating back thousands of years. They often recorded what they called "guest stars" that appeared where no star had previously been observed. Guest stars were often extremely bright for a short time then gradually faded back into their familiar obscurity. According to Chinese records, on July 4, 1054 AD a very bright guest star appeared, at the current position of the Crab Nebula. It was close to the star, Zeta Tauri. At its peak this guest star was visible in the daytime for a period of 23 days. It slowly faded and disappeared from view altogether in the spring of 1056, nearly two years later.
We now know that these guest stars are stellar explosions and call them either novae or supernovae. Only involving the surface layers of a white dwarf star, novae are less violent explosions than supernovae. The Crab Nebula is the remnant of the supernova that the Chinese observed on July 4, 1054. Supernovae explosions are the death throes of massive stars.
Other Observations
Chaco Canyon, in western New Mexico, is the site of some Anasazi ruins. The Anasazi are the ancestors of the modern day Pueblo people of the American southwest. Their civilization flourished about 1000 AD. The Anasazi may have observed and recorded the formation of the Crab Nebula. There is a petroglyph at Chaco Canyon showing what appears to be a crescent moon near a very bright star. On July 5, 1054 the crescent moon was very close to the position of the Crab Nebula and the supernova that formed it.
Curiously there are no known European observations of this supernova.
Many communities across the US still commemorate the date of the Crab Nebula Supernova with fireworks. :-)!
Further Reading
Zeilik, Michael, Astronomy the Evolving Universe, 9th edition, Cambridge, 2002.
