It may seem that when you look up into the night sky that the stars are unchanging. But, consider the relative time scale between a human life and the lifetime of a star. It takes between millions and billions of years for a star to develop from a cloud of cold dark gas through its life time until its eventual demise when it runs out of fuel and explodes in a fiery explosion called a super nova (Kaufmann & Freedman, 1999, p. 520). This difference in time scale makes direct observations of stellar evolution impossible during a human lifetime.

    A supernova explosion shines with a luminosity a billion times greater than our sun (Kaufmann & Freedman, 1999, p. 552). Many were bright enough to be seen and recorded during the course of human history, despite being relatively great distances from the Earth. Modern science has learned a lot about the interior of massive stars by studying the light emitted in the final hours of a star’s life. The heat created within the explosion is the only place known in nature where elements with atomic weights heavier than iron are created (Begelman & Rees, 1996, p. 40).

    The Chinese saw changes in the heavens, such as supernovae, as precursors of changes to happen here on Earth. Their interpretation has been supported by modern science. Every element on Earth and in our Solar System, other than hydrogen and helium, was manufactured in the cores of massive stars or during supernova explosions (Kaufmann & Freedman, 1999, p. 548). Changes in distant stars were the precursors to the current cosmos’ composition. Without supernovae and massive stars the elements of life may have never come into existence.
 

Types of Supernovae
 
    Within the current models of supernova there are two main classifications. The basis for these classifications is the presence or absence of hydrogen emission lines in the spectra of the light emitted by the explosion. Type I supernova have no hydrogen spectral lines (Petschek, 1990, p. 1). One current model for a type Ia supernova is a white dwarf pulling mass off of a giant companion star until it reaches the Chandrasekhar limit of 1.4 solar masses (Begelman & Rees, 1996, p. 32). The Chandasekhar limit was discovered by the Indian-American scientist Subrahmanyan Chandraesekhar who did some of the first theoretical models of white dwarves (Kaufmann & Freedman, 1999,
p. 546). At 1.4 solar masses the electron degeneracy forces cannot support the weight of the star and it collapses (Kaufmann & Freedman, 1999, p. 558). Electron degeneracy is the point when electrons cannot be further compressed because of pressure drops  (Kaufmann & Freedman, 1999, p. 546). This model would account for the absence of hydrogen in a type Ia supernova’s spectra because the star has already burned away most of its hydrogen during its main sequence life. It then shed the rest as it went from its red giant phase to a white dwarf.

    A type II supernova has the spectral lines for hydrogen (Petschek, 1990, p. 1). Type II explosions are thought to be very massive single stars that produce an iron core of 1.4 solar masses. The core is layered through a chain of thermonuclear reactions during the expansions and contractions in its giant or supergiant phase. The hydrogen spectral lines are produced by the hydrogen in the outer layers of the star as they are excited by the huge amounts of energy released by the breakdown of all the fused atoms in the core (Kaufmann & Freedman, 1999, p. 558).

    There are still many inconsistencies in the classification of supernovae. Some type I explosions start to show hydrogen in their spectra later in the explosion (i.e. supernova 1993J) (Murdin, 1993, p. 668). The classification of supernovae is still in its infancy and much remains to be explained. For our purposes we will focus on type II explosions since they are less complex than binary models and are better understood.
 

Physics of a Type II Supernova

    Stars of low mass live very long lives because they burn their fuel relatively slowly compared to massive stars that expend their fuel quickly. This is due to the higher gravity inside a massive star that the thermonuclear reactions must keep up with in order to maintain the mechanical equilibrium of the star. All stars go through a phase of stellar evolution called the main sequence when they are converting hydrogen to helium. This period is the longest, most stable time in a stars life. Current models show that after the main sequence stars of masses lower than eight solar masses go through a series of expansions and contractions as they start to fuse heavier and heavier elements (Kaufmann & Freedman, 1999, p. 550). However, these stars do not have enough gravity to contract and reach the temperature needed to create iron. Eventually they shed their outer layers leaving a mostly carbon core -- a white dwarf. These stars can remain in gravitational equilibrium indefinitely (Begelman & Rees, 1996, p. 29).

    As a massive star runs out of hydrogen to convert to helium it moves off the main sequence in a series of contractions and expansions similar to a smaller mass star. The star contracts when it runs out of the fuel it is burning in the thermonuclear reaction at its core. The contraction causes the core temperature to rise until it reaches the necessary temperature to accelerate the particles in its core to speeds high enough to overcome the electric repulsion between the protons and start the next reaction in the chain (Begelman & Rees, 1996, p. 31). During this process of contraction and expansion the star can eject much of its mass. If the star remains massive enough it will move through the chain of reactions until iron is created.

    No further fusion reactions are possible beyond iron without an input of energy. The core collapses under the weight of the star’s outer layers. The outer layers fall inward as the pressure in the core suddenly drops. As the core reaches the density of an atomic nucleus the electrons and protons are forced together creating neutrons and releasing on the order of 10^57 neutrinos. Neutrinos are particles that react with other particles very infrequently, but the 10 percent that do interact with another particle on their way out of the core may push the pressure wave through the star’s outer layers (Begelman & Rees, 1996, p. 33-34).

    At this point the core becomes stiff because the neutrons cannot be compressed any further. The outer layers of the star are reflected back outward. The pressure wave that is created compresses and carries the outer layers of the star out into space. This enormous pressure and energy input from the neutrinos interacting with other particles heats the material traveling in the pressure wave to temperatures high enough to fuse elements heavier than iron. This is the only place in any natural system that elements heavier than iron can be created (Kaufmann & Freedman, 1999, p. 551). When the pressure wave reaches the surface of the star it blows off the outer layers into space in a supernova explosion. At this point the supernova becomes visible. The energy released in a supernova explosion is about 10 times the amount of energy released over the whole life of the star. Gravity is the force that releases the majority of a stars energy over its whole life, not its thermonuclear reactions (Begelman & Rees, 1996, p. 32). It does so within the last seconds of its life, creating a supernova.
 

What's Left After a Supernova

    Besides being dense neutron stars have intense magnetic fields. The field is intensified by the compression of the magnetic field lines in the star as the core collapses. This creates a magnetic field about 10^9 times that of an ordinary star. (Begelman & Rees, 1996, p.  46) These magnetic field lines accelerate electrons toward the star’s poles creating synchrotron radiation. This radiation ionizes the gas in a supernova remnant causing them to emit visible light (Begelman & Rees, 1996, p. 43). When the electrons reach the poles they are emitted in an intense beam of radiation, usually radio, which sweeps through space as the star's magnetic poles precess (Begelman & Rees, 1996,
p. 55). This phenomena has been observed in pulsars such as the one in the Crab Nebula.

Observations

    We observed two stars that are candidates for supernova explosions in the near future, relative to the time it takes a star to move through its life cycle. The first star we observed is Betelgeuse. It lies in the constellation of Orion at his upper shoulder. Observing with 10x50 binoculars on April 13th at 9:30 P.M. we noticed its reddish color. Through a 10” Newtonian reflector less color was visible. The low surface temperature of Betelgeuse, approximately  3000 Kelvin (Menzel & Pasachoff, 1983, p. 434), causes its peak radiation to be tilted to the red end of the scale. On the night of April 13th at 9:30 P.M. Orion was visible looking due West, close to the horizon.

    Betelgeuse’s distance from the Earth is 310 light years.  It is one of the brighter stars in the sky with an absolute magnitude of -5.6. Its spectral class is that of a M2 luminosity class I (Menzel & Pasachoff, 1983, p. 434). The H-R diagram shows that Betelgeuse is a cool star, but very luminous due to its large radius. It has a radius close to a thousand times that of our sun (H-R diagram workshop, 5-18-99). Betelgeuse is a good candidate for a supernova because it is late in its life, and has a large radius. Current models show that Betelgeuse has already built up a layered core structure due to a series of contractions and expansions while raising its core temperature high enough to burn heavier and heavier elements in its core.

    Antares is the second star we observed. It was visible on April 20th at 2:00 A.M., just above the Southern horizon. Antares is also a massive supergiant that may be nearing the end of its life. We observed with 10x50 binoculars and noted its reddish tint. It is about 2.5 times dimmer than Betelgeuse with an absolute magnitude of -4.7. Its spectral class/luminosity class is a M1 II (Menzel & Pasachoff, 1983, p. 434). Antares is located near the center of the constellation of Scorpio.
 

    The traditional Chinese view of the universe differed greatly from traditional Western views. The Chinese did not feel the need to explain the creation of the universe. They saw human beings and the cosmos as the natural state of being. The world needed no outside influences or beings to justify its existence. Western societies tend to see the world in more linear terms, having a set begin and end. Seeing the world in these terms influences the way that Western civilizations interact with the world around them. Traditional Western creation myths show that the existence of humans and the world that surrounds us could not have come into being through natural processes because of the complex nature of the universe. Therefore, outside forces must have been at work. The Chinese Daoists view “… the cosmic origin as Wu, or nonbeing, the primal condition of the cosmos as hundun, or ‘chaos’, and the cosmic formation as a continuous process” (Ren, 1998, p. 4). This view meshes well with the current theories of evolution and the progression of the planet Earth.

    Chinese emperors employed astrologers to watch the skies day and night to look for any changes in the cosmos. Any events observed would be interpreted by the astrologers. These interpretations were based on Chinese modes of correlative thought. The most common correlation was between the human body and the heavens. This was demonstrated by the use of numerology to relate the human body to natural cycles. One example is from the Han era text Huai-nan-izu cited by Henderson (1984) in The Development and Decline of Chinese Cosmology.

 Heaven has nine layers, and man likewise has nine orifices. Heaven has four seasons with which to regulate the twelve months. Man likewise has four limbs with which to employ the twelve larger joints. Heaven has twelve months with which to regulate the 360 days (of the year). Man likewise has twelve minor limbs with which to employ the 360 lesser joints (p. 3).

    This quote shows how much the Chinese believed in the unity of the cosmos and the human body. They believed that if you try to ignore or work against these correlations you were sure to fail. Not only would you be sure to fail, but you would be working toward harming yourself because of the close correlation between the body and the cosmos. Every aspect of their universe was seen as a portion of a larger whole.

    The second place that the Chinese drew a correlation with the cosmos was in the government and its offices. This correlation gave the imperial government a cosmic importance that could not be disputed. This system dates back to the early Han era, circa 200 BC (Henderson, 1984, p. 5). The sky was divided into several hundred regions, asterisms, that contained an average of five to six stars (Clark & Stepheson, 1977, p. 33). These regions corresponded to certain governmental offices, states, or objects. Observed changes in these regions were correlated to predict changes in the corresponding area, object, or office. The timeline for these predictions was comfortably long, giving ample time to identify an event that fulfilled the prediction. One example that Clark and Stephenson (1977) refer to is found in the ancient text the Chin-shu.

4th year of the T'ai-ho reign period of Hai-hsi, 2nd month. A guest star was seen at the western wall of Tzu-wei. When we came to the 7th month it finally disappeared. The interpretation when a guest star guards Tzu-wei is the assassination of the Emperor by his subjects. In the 6th month Huan-wei dethroned the Emperor who became the "Duke of Hsu-hsi" (p. 33).

    The date of this observation is 369 AD. The five-month duration of the "guest star" being visible suggests that it was possibly a supernova or comet.

    The Chinese astrologers have provided us with the most complete, continuous record of observations in history. Their record dates back to the early Han dynasty, 213 BC, when the emperor Ch'in Shih-huang started a systematic censorship of all records that did not agree with the current philosophy (Clark & Stephenson, 1977, p. 5). This record has proved very useful to modern astronomers who have been using it to look for sightings of ancient supernovae, novae, or comets.

    For the Chinese the appearance of a supernova in the heavens corresponded with a coming change in the political system. The Chinese felt that the cosmos, state, human body, and society were all a part of the same interrelated system that could not be separated. Han era cosmologists felt that any unusual events in the heavens (i.e. comets, eclipses, and "guest stars") were repercussions on a cosmic scale of a ruler’s misdeeds (Henderson, 1984, p. 37). The balance can swing both ways with the actions of humanity affecting the heavens and the observed changes in the heavens foretelling of coming changes in the human world. This way of looking at the world brings humanity back to the natural cycle instead of elevating him above nature. This is a lesson that could be useful within the Western societies of today.
 

    In contrast to China and the Middle East where cosmic events, including supernovae, were almost always recorded by observers, sightings of supernovae went almost completely without mention in Europe. There were a few exceptions to this, but in general they went either unnoticed, or in the cases of some of the brightest supernovae, ignored. There were a few sightings here and there, but for the most part records of European sightings remain rare. This lack of records would have been hard to maintain considering the brightness and visibility of some of the supernovae that could have been seen in the skies over Europe. While in China many “guest stars”, or supernovas, were not only recorded but used to predict dynastic changes, social prosperity, or unrest. Europeans who also had considerable knowledge of the sky just went about their daily lives ignoring the existence of such notable cosmic events. There were some sightings, but too few considering the number of supernovae that would have been visible in European skies (Murdin & Murdin, 1985, p. 7).

    One good example of a European sighting is the supernova of AD 185. A description by Herodias of Rome in AD 250 mentioned a star that "shown continuously by day". He seems to be referring specifically to the star that exploded in 185 AD (Murdin & Murdin, 1985, p. 7). There was also a 4th century history of the reign of Emperor Commodus that seemed to refer to the same event as it occurred right before the a civil war. He describes the heavens as being “ablaze” (Murdin & Murdin, 1985, p. 7). Another European sighting took place in 1006 AD, and is the most significant account of a supernovae in Europe before the age of Brahe and Kepler. It was sighted by a monk in Switzerland who wrote the Pars Altera (919-1044 AD), a chronicle of the Benedictine Abbey at St. Gall (Murdin & Murdin pp. 7, 15). Beyond these two sightings Europe was for the most part silent and indifferent to cosmic events. The sighting of 1006 AD was the last before Tyco Brahe saw one centuries later.

    How could the Europeans have managed to ignore these dramatic cosmic events? In 1054 AD a supernova that was as bright as Venus lit up the European sky. It was visible in daylight for three weeks, and visible in the night sky for two years. It is believed to be the brightest supernova that shone in our skies during all of recorded human history. It was sighted by both Chinese and Japanese astronomers and is believed to be the present day Crab Nebula. Yet there was not one mention of it in all of European annuals (Murdin & Murdin, 1985, p. 7). One proposed explanation for the lack of records of this supernova is that its appearance coincided with the split in Christianity between the Roman Catholic Church to the west and the Greek Orthodox Church in the east. Events were leading up to the split between July 16 and 24, 1054 when the formal break occurred between the patriarch Michael Cerularins and Pope Leo IX. This was also known as the Great Schism. During such a time of turmoil it might have been dangerous to record such a notable cosmic event. It doesn't seem beyond belief that the church Fathers might have destroyed any records of the supernova of 1054 (Murdin & Murdin, 1985, pp. 7-8).

    The next supernova was not the first to be seen in Europe, but the first one to be seriously studied in 1572. The first observation was made on November 6th by Wolfgang Schuler of Wittenberg (Moore, 1973, p. 95). He saw the star in the constellation of Cassiopia. On November 7th it was also sighted by Paul Heinzel of Augsburg, Bernhard Lindauer of Winterthur in Switzerland, and Michael Mastin of Tubingen. But the most famous person to see the star and the person who received the fame for seeing it was a Danish astronomer Tyco Brahe. Brahe was at the beginning of his career in 1572, and it was this supernova that inspired him to devote his lifetime to making accurate measurements of the positions of the stars and planets (Dreyer, 1963, p. 38; Murdin & Murdin, 1985, p. 27). Brahe had just recently invented a new sextant that allowed him to measure the distances between stars and to find the exact position of the New Star and measure its angular distance from the stars in Cassiopia. Interestingly enough, Brahe’s sextant was not much more precise than the accuracy needed to measure the annual parallax of the stars. He kept track of the star until it disappeared from the sky eighteen months later (Moore, 1973, p. 97). His measurements were accurate to a 10th of a degree, and he found that its position remained unchanged (Dreyer, 1963, p. 39; Murdin & Murdin, 1985, pp. 28-29).

    Some of Brahe’s contemporaries advanced the position that perhaps it was moving directly away or directly toward Earth, but these explanations didn't hold. If it had been a comet and moving across the sky like comets normally do, Brahe would have detected its motion in a period of hours. Over many months he detected no motion whatsoever, ruling out the possibility that it was a comet or a planet. The farthest known planets’ motion at the time would have been evident within a week, and this object hadn’t shown any motion for far longer than that. In addition to these arguments the fact that planets shine without twinkling was used to show that this was indeed a star (Dreyer, 1963, pp. 41-43; Murdin & Murdin, 1985, p. 29).

In the De Stella Nova, Tycho Brahe wrote,

I conclude this star is not some kind of comet or fiery meteor, whether these are generated beneath the moon or above the moon, but that is a star shining in the firmament itself one that has never been seen before in our time or in any stage since the beginning of the world. [Later he wrote] that in the ethereal region of the celestial world no change of generation or of corruption occurs . . . but celestial bodies always remain the same like unto themselves in every way (Murdin & Murdin, 1985, p. 28).

Evidently his argument was that God had masked the supernova from earthly eyes since the creation, choosing to reveal it at any time.

    On October 17, 1604 AD, Brahe’s former assistant Johannes Kepler saw a new star that he described as competing with Jupiter in brilliance and colored like a diamond. It had been sighted just days before by a pair of Italians and an astronomer by the name of I. Altobellie in Vienna. On October 10th, J. Brunowsky, a court official in Prague, caught a glimpse between the clouds of the new star and notified Kepler. (Murdin & Murdin, 1985, p. 31). Kepler made arrangements to continue his observations, but in November the supernova moved too close to the sun to be seen. It reappeared in January, but was fading, continuing to be invisible until October of 1605 AD, and was carefully observed by Kepler and others until then (Murdin & Murdin, 1985, p. 31). After the supernova of 1604 AD the next supernova able to be sighted with the naked eye was relatively recent in 1987. This supernova was our first good chance at understanding the nature of these awesome cosmic events.

    The history of European observations of supernovae had been lacking up until the modern era. Since Kepler, no supernova have been recorded in our galaxy. In 1987, a star exploded in the Large Magellanic Cloud, a galaxy neighboring our own. Before the era of modern physics and space exploration, European records tell us very little of the sky. The lack of records may reflect more on the Europeans themselves and their view of an “unchanging” cosmos. The 1054 AD supernova was only seen by one monk in Switzerland. Europe’s lack of acknowledgment of these cosmic events for most of its written history until the age of Kepler and Brahe is striking, and reflects the power that European religions held over ideas about the cosmos. A universe centered upon the Earth rather than filled with billions of stars and having no center.
 
 
 
Bibliography

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A scientific analysis of historical records of supernovae and how they relate to modern science and visible remnants visible today. In general and scientific terms.

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A book on recent developments in astronomy and the historical development of modern theories on how the universe works.

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Star charts and practical guide to viewing as well as information on brightest stars in sky.

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