Sunday, November 7, 2010
Those who have read my most recent note know that I am fascinated by light. I consider light the essential phenomenon in so many ways.
Biblically Jesus referred to himself as the light of the world. "Again Jesus spoke to them, saying, ‘I am the light of the world; he who follows me will not walk in darkness, but will have the light of life.’ “(John 8:12 RSV) And we are told to shine the light. ”You are the light of the world — like a city on a hilltop that cannot be hidden.” Matthew 5:14 NLT)
Light is the primary means of experiencing the wonders of creation, from sunrise to sunset, from a baby’s smile to the smile of your baby, from the nearness of a microscopic view of tissue to the "farness" of the distant stars. Light is the primary way we communicate with the creation. (Of course we also have touch and taste as well as hearing, but none of these senses give us the near/far perspective we obtain from light and vision.)
Light is key to much of modern physics from the study of optics and gravity by Sir Isaac Newton to the study of electromagnetic forces and Maxwell’s equations to the discovery of the special theory of relativity and the general theory of relativity by Einstein to the black holes of Karl Schwarzschild and Stephen Hawking. As I have already related, it was in the deep study of Maxwell’s equations that I reached the pinnacle of my scientific studies and comprehension. I saw the light!
And it is light that gives us life here on the earth. With all the discussion about energy and nonrenewable and renewable sources of energy, it may not be apparent that all energy comes form the sun. Either directly in the heat that gives us wind power and water power to the plants that give us coal and oil. Even the energy of radioactive materials found in the earth had their birth place in the stars — and our sun is just one of many stars — albeit the closest.
So let’s talk about stars or suns. As the night sky will testify, there are many, many stars in the sky. Most are very distant with the nearest night time stars Alpha Proxima. This is a triple star formation in the constellation of Centarus. These stars are approximately 4.2 light years from earth. That is, it takes 4.2 years for the light, traveling at just under 300,000 miles per second, to reach us. But, of course, there is a much closer star, the one we call our sun. Its formal name is “Sol.” Sol or our sun is approximately 93,000,000 miles from the earth. That means the light from the sun or Sol reaches us in just 8.3 minutes.
Our sun is not particularly special in the spectrum of all the stars, and thank God for that. The fact that our sun is rather ordinary and steady is key to life on this earth. It is not the biggest sun by far, but not the smallest either. You see, stars (or suns) have a life cycle. They are born, they live, and they die. However, the timescale on which this occurs is millions of years.
So where does sunshine or the light from the sun come from? This is a question that has intrigued mankind for thousands of years. Ancient myths had the sun as a large burning object carried in a chariot across the sky. Many ancient cultures recognized the sun as key to life with its warmth and light, and even made it into a god. Genesis tells us that the Lord placed the Sun in the sky to govern the day, and rule it does. Due to the bright light of the sun most stars and even the moon cannot be seen during the day. Only the very brightest can compete with Sol during the daylight, and have to wait for nightfall to make their presence known.
Before we start discussing just what makes sunshine, let’s do a little review of physics. As you all remember, all matter (or stuff) is made up of atoms. These atoms are combinations of three atomic particles. First are electrons. Electrons are negatively charged and orbit around the atomic nucleus. In the nucleus are protons and neutrons. Protons have a positive charge and weigh a little more than 1000 time as much as an electron. Neutrons are electrically neutral and weigh an amount about equal to a proton plus an electron.
Electrons, being negative, are attacked to the nucleus which is positive. This is called electrostatic attraction and, as you all recall, unlike charges attract. But what about all those positive protons so tightly packed in the nucleus? Since like charges repel, what holds these particles together? The answer is something called the “strong nuclear force.” This force only operates at very short distances, but it is responsible for keeping the nucleus of an atom together.
There are only four fundamental forces in the universe. Gravity, which holds us bound to the earth and earth bound to the sun; electromagnetic force, which is much, much stronger than gravity and binds the electrons to the nucleus; strong nuclear force (also called the “strong interaction") which is able to overcome the repulsion force of the electromagnetic force and binds the protons to the nucleus, and finally the weak nuclear force (or weak interaction) which is also present in the nucleus of the atom and binds the proton together.
Binds the proton together? I thought a proton was as small as it gets? No, these three fundamental atomic particles, the electron, the proton, and the neutron, are thought to be made up of even smaller particles called “sub atomic particles” and this is the frontier of modern physics as these subatomic particles are explored and explained. The strong and weak interactions will become important as our discussion of sunshine continues.
Now that we have the atomic components down, let’s start building atoms. It is the number of protons in an atom that determine the element. For example, an atom with only one proton is called hydrogen. If it has two protons, it is helium. And so on through the periodic table. Oxygen has 8 and Iron has 26 protons. At the higher end of the table we find lead with 82 protons and uranium with 92. There are some elements, very short lived and not found in nature with over 110 protons, but these elements are very unstable and don’t last very long before splitting into atoms with less protons.
So, with an understanding of these basic building blocks, what makes them shine, how do they grow, and how do they eventually die. A star is born when a massive cloud of hydrogen gas, many times the size of our solar system, is slowly compressed by the force of gravity. The gravitational force compressing the gas gradually heats up the gas, as gravitational energy is converted into the kinetic energy of the hydrogen atoms.
As temperatures keep increasing, the electrons are torn out of their orbits and you get a soup of electrons and nuclei called a "plasma." Plasma is the fourth state of matter after solid, liquid, and gas.
Normally, the repulsive charge of the protons within the hydrogen plasma is sufficient to keep the atoms apart. But at a certain point, when the temperature rises to 10 to 100 million K (a measure of temperature similar to Celsius, but with no negative values) a nuclear reaction occurs. (Zero K is absolute zero, and lowest possible temperature, which is -273.15 degrees C. So 10 to 100 million K is hot, hot, hot.) At this temperature, the kinetic energy of the protons (which are just hydrogen nuclei) overcomes their electrostatic repulsion and they slam into one another. The nuclear force then takes over from the electromagnetic force, and the two hydrogen nuclei “fuse” into helium, releasing vast quantities of energy.
This is called nuclear fusion. The energy released is related to a conversion from mass to energy given by Einstein’s equation e = mc2. That is a small amount of mass (the quality of matter that gives it weight) is lost since the nucleus of helium weighs slightly less than than the nucleus of two hydrogen atoms. Recall that c, equal to the speed of light, is a very large number, and in this equation it is squared making it much, much larger. So a tiny amount of mass converted to energy yields a tremendous amount of heat and light.
In other words, a star is a nuclear furnace, burning hydrogen first and creating nuclear “ash” in the form of waste helium. A star is also a delicate balancing act between the force of gravity, which tends to crush the star into oblivion, and the nuclear force, which tends to blow the star a part with the force of trillions of hydrogen bombs. A star then matures and ages as it exhausts its nuclear fuel.
Our sun is a “yellow” sun. That is the burning of hydrogen into helium produces a spectrum of light in the yellow range. This light can be modeled by stating a temperature in Kelvin that a large black body would have to be heated to so it would produce the same spectrum of light. Sunlight is modeled as 5,000 K. As this light is reflected and refracted during the day, it can be modeled as between 5,000 and 6,000 K. Lights that are designed to simulate sunlight would be in this range. Incandescent lights designed for use with photography and simulating this color of light have been around for a long time. What is new is fluorescent bulbs that produce light in this color range. These fluorescent bulbs are a great benefit to photographers and videographers because they produce much less heat than incandescent and don’t require as much power to operate. I have a complete range of soft and hard light sources using these special bulbs, and they are a lot cheaper and lighter and easier to use.
I won’t get into the evolution of stars and how they change as the hydrogen is eventually exhausted. The final result can be everything from a “red giant” to a “white dwarf” and even a supernova and neutron star or pulsar. Under certain conditions stars may actually evolve into black holes. These are such massive stars that even light cannot escape the pull of gravity, and so they appear black.
Our own Sol is about 5 billion years old. It is considered a middle aged star, and should burn for anther 5 billion years before its supply of hydrogen is exhausted, so you don’t need to get too worried about the sun burning out in our life times. When one first hears the life history of stars, one may be a bit skeptical. After all, no one has ever lived 10 billion years to witness their evolution. However, since there are uncountable stars in the heavens, it is a simple matter to see stars at practically every stage in their evolution. For example, the 1987 supernova, which was visible to the naked eye in the southern hemisphere, yielded a treasure trove of astronomical data that matched the theoretical predictions of a collapsing dwarf with an iron core. Also the spectacular supernova observed by ancient Chinese astronomers in 1054, left behind a remnant, which has now been identified as a neutron star.
Before I close, I mentioned the nearest star other than our own sun, but what is the farthest star we’ve observed? Well that honor is currently held by a star discovered on April 27, 2009 — a self-destructing star that exploded 13.1 billion light years from Earth. It detonated just 630 million years after the big bang, around the end of the cosmic "dark ages", when the first stars and galaxies were lighting up space. The light from this early star is giving us a front row seat to the most ancient of creations.
Just like my daddy used to say …
He used to say soul shine,
It’s better than sunshine,
It’s better than moonshine,
Damn sure better than rain.
Yeah now people don’t mind,
We all get this way some time,
Got to let your soul shine, shine till the break of day.