July 4th. For those of us in the United States, this is an important date to remember the adoption of the Decleration of Independance by the original 13 colonies…our Independance Day. But in the astronomy world, this date is famous for another event: SN 1054
SN 1054, or Supernova 1054, is a story that many astronomers hear about early in their studies of the heavens. Loosely quoting what I had heard, “A new star suddenly appeared in the sky. First recorded by the Chinese, it was so bright that it could be seen for a almost a month during the day, and for almost two years at night. This new star was the explosion that caused the Crab Nebula to form.”
Wait. A new star; visible during the day; an EXPLOSION? What exactly are we talking about? Well, a supernova, to put it in it’s simplest explanation, is a massive stellar explosion. Not all stars go through such a death…ours definitely won’t…because it occurs in one of two ways.
One involves only really massive stars. Think of a star as a big factory of energy. The energy is created as the parts inside interact. But each time they interact, these parts make a minor change into something else. So we have part A and part B. When all of the part A’s run out, the part B’s start interacting, changing into part C’s. The larger the star, the more parts they can change into. But each time a new set of parts start interacting, more work is required to make them change into the next part. Part A may take BILLIONS of years to completely change. Part B may take a few billion years less. Part C may only take millions. By the time you reach part H, it may only take a few days. This is a simple explanation for Nuclear Fusion.
As a really massive star reaches the point where it only takes days or hours to go through nuclear fusion, it has also not only increased in size, but the gravity generated is much stronger. If the conditions are right, the gravity overpowers the expansion of the star and the star collapses in…VIOLENTLY. The energy created is so powerful that an explosion, or NOVA occurs. A Supernova is when an even larger star generates a really powerful Nova.
The other way it could happen involves a few scenarios that require particular types of stars to work. Either Star A feeds, or sheds material off of a closely orbiting Star B, or Star A and B merge with each other, causing a rapid change in stellar conditions that can cause an explosion.
We’ve learned that supernova’s occur more frequently than we considered, but most come and go without ever getting the kinds of attention SN 1054 might receive. Outside of the astronomy world, you’d probably never even hear about them. Unless it is bright enough to be seen by the naked eye. Then it usually gets some attention. But SN 1054 is special for another reason…documentation.
Even though this occured almost 1000 years ago, how is it possible to reliably predict the exact date? That would be a good question. It IS a good question. Thankfully, astronomy has been an active study for much longer than 1000 years and a number of historical documents mention this “Guest Star”, as the Chinese often referred to it and other sudden appearances of stars. Many of these documents mention specific days, using the Chinese calender, which can be transcribed to their respective days in our Gregorian calender used in modern times. Taking into account possible typo’s, several documents point to July 4th.
Additional documents exist from Japan and a single reference in Arab literature. Mistakes seem to be found in these documents that make them hard to vet. The Japanese documents all share what appears to be a common mistake, which if taken into account alongside a few other oddities, resets those dates to roughly July 4th. The Arab document also contains some inconsitencies that seem to make sense when examinging differences in calenders and references to other phenomenon mentioned within the document. European documents seems to have some serious problems so they aren’t very reliable. Evidence indicates they were possibly made with limited astronomical knowledge. A few possible Native American references exist, but are unconfirmable.
It is because of the documentation that SN 1054 is so important. It is a result of these documents that when the Crab Nebula shows up again in astronomical documents, roughly in the mid-1700’s, historians and astronomers started putting two and two together. It gained noteriety in 1758 when Charles Messier listed it as the first item on his new catalog of comet-like objects. It gained it’s common name in 1848 by the Earl of Rosse when he noted it’s similarities with a crab. And it’s identification as a supernova remnent and it’s link to SN 1054 were established in the early half of the 20th century by several astronomers, including Edwin Hubble, namesake of the Hubble Space Telescope.
This makes the Crab Nebula, and it’s host event SN 1054, one of the more famous examples of a supernova, and one of the few, if not the only, to be confirmed by historical documents.
So now, when asked why July 4th is so important, you can add a footnote about it’s importance to astronomy and our study of the heavens.