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--------------------- 2402 - LIGHT - There is not enough light
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- The Full Moon is ½ degree of sky. There are about 15,000 galaxies with billions of stars and 1,500 individual stars in ever area of sky that is about this size. This only assumes you can see down to a dimness magnitude of 24. If you can see down to a dimness magnitude of 27 than you would see ten times these numbers.
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- There is a new telescope under design that will cover 10,000 degrees of sky every 4 nights to a dimness magnitude of 27. It will create petabytes of image data that needs to be cataloged and data-mined by astronomers. (petabyte is a thousand, million, megabytes).
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- Once the population of distant galaxies are cataloged they can then be used as gravitational lenses to see even more distant galaxies directly behind them. At the same time the warping of visible matter will map the Dark Matter that is creating the gravity that is doing the lensing. When this is repeated many times a 3D Universal map of Dark Matter will be available for astronomers to study the evolution of the Universe.
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- This is not meant to dismiss the importance of starlight. Every living thing on Earth depends on starlight, or what we call sunlight. Well almost, there is life existing in the deep oceans around volcanic vents in the ocean floor.
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- These bacteria live off the hydrogen sulfide that comes out of the vents. These critters are living off chemical energy, not light energy. By the way, hydrogen sulfide is poisonous to us humans. Even 600 molecules of hydrogen sulfide per million molecules of air could kill you.
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- Plants live off sunlight by trapping its energy, taking CO2 from the atmosphere, taking some water from the soil and creating sugar. When you eat plants and digest sugar you are getting chemical energy back from sunlight.
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- Even meat eaters living off the top of the food chain at some stage find a smaller form of life living off something green, that is plant sugar. There is a special molecule , called chlorophyll, that captures photons from sunlight. The energy from the photon is used to make water, H2O, and CO2 stick together to make sugar.
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- The pigment of this sugar is green. Some plants move the sugar underground and store it in the roots as starch. When you eat a potato you release the energy trapped in the sugar and you put the CO2 back into the atmosphere. Eating fries can be environmentally unfriendly creating global warming.
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- The human body does not use reverse photosynthesis to get the energy back. The body has a different process using a molecule called, adrenosine triphosphate. The process is called metabolism.
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- The unit of energy in physics is called a “joule”. It is kilograms * meter^2 / second^2. These units come directly form Einstein’s equation E-mc^2. Mass is kilograms and c^2 is velocity in meters / second squared. Energy and therefore joules can not be created or destroyed. They can only be changed from one form of energy into another, on in an extreme case into mass, which is a special form of energy.
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- The human body uses about 2,500 Calories of energy every day. Calories with a big “C” is the same as 1,000 chemistry calories, with a little “c”. A Calorie is another unit of energy and it is equal to 4,184 joules. So, that many Calories per day is 10,460,000 joules of energy.
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- A watt is a unit of power and power is the amount of energy consumed over time. Power is the rate of using energy, it is the rate-of-change of energy. One watt is one Joule / second. Watts are kilograms * meter^2 / seconds^3.
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- A day is 86,400 seconds. So, 2,500 Calories corresponds to 120 watts. Your body is emitting about the same amount of energy per day as a 120 watt light bulb. No wonder you shine in front of an infrared camera and snakes can see you at night.
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- We humans got the privilege of naming ”light” so we mean visible light to us. Bees can see in the ultraviolet light which is invisible to us. Light gets bluer and bluer to us then disappears into the ultraviolet. Many flowers that look boring to us are a very bright, vibrant color in ultraviolet.
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- Some snakes hunt at night because they can see in the infrared. Light that gets redder and redder to us will disappear into the invisible. But, these snakes can still see just fine in their hunt for food.
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- Your average household in America uses about 900 kilowatt-hours of electricity per month. This usage is 900,000 watts in 3600 seconds, or 250 joules per second per second. A month is 2,630,000 seconds. So, in a month your household uses 658,000,000 joules of energy. So, your household electricity is burning the energy of about what 67 people do a day, or 2.2 people burn in a month.
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- When men are sleeping they burn about 65 Calories per hour. When they are running the burn about 600 Calories per hour. So, on an average diet of 2,500 Calories per day a man could not run for more than about 4 hours, burning just this diet.
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- However, men could watch TV using 80 Calories per hour, which would last 30 hours, which means they would store 6 hours worth of fat on the average diet for every day watching TV.
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- If you are listening to a radio station, say AM at 1,120 KHz on the dial, you would be receiving light energy that you could not see but each radio photon is a packet of energy.
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- Photon Energy = Planck’s Constant of Action * frequency. E=h*f. Action in physics is the product of energy and time. Action is in joule*seconds. The energy of the radio photon is 6.626*10^-34 joules*seconds * 1,120,000 cycles per second. So every radio photon is 7.42*10^-31 joules. That is a very small amount of energy.
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- Let’s say you step outside to catch some tanning rays. You soak up the Sun’s ultraviolet photons that are at 120 nanometers wavelength. Since wavelength times frequency = velocity , and the velocity of light is constant at 300,000,000 meters per second. The frequency of the ultraviolet photon is 2,500,000,000,000,000 cycles per second. The energy of these photons is 17*10^-19 joules. These UV photons have a trillion times more energy than the radio photons.
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- Let’s say the dentist gives you a teeth X-ray to discover cavities. An X-ray photon is 10,000 electron-volts. 1 electron volt is 1.6*10^-19 joules. So, the X-ray photon is 1.6*10^-15 joules of energy. The X-ray photon is 10,000 more energy than the UV photon.
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- A 100 watt incandescent light bulb produces its light energy by electrically heating up a tungsten coil to a temperature of 3,000 Kelvin The surface temperature of the Sun is 5,800 Kelvin.
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- The color of light and the temperature are related by a formula. Color is another name for the wavelength of light. The peak wavelength emitted = 2,900,000 nanometers / Kelvin So the peak wavelength of the incandescent bulb is 970 nanometers. 970 nanometers is in the infrared spectrum. No wonder the bulb gets so hot.
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- The peak wavelength of the Sun’s surface is 500 nanometers. This color is greenish-yellow. It is the Earth’s atmosphere that scatters the blue light and makes the Sun yellow. This difference in peak wavelengths, 970nm versus 500nm, is the reason professional photographers use to use different types of film for indoor photography and for outdoor photography.
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- The total radiation, or light power, coming from the Sun is 4*10^26 watts, 4*10^26 joules / second. The radius of the Sun is 7*10^8 meters, therefore, its surface area is 4*pi*r^2 = 6.16*10^18 meters^2. The watts per square meter is 65,000,000 watts / m^2.
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- The 100 watt bulb is emitting its power at a peak wavelength of 970 nanometers for a temperature of 3,000 Kelvin. The frequency is calculated to be 3.1 * 10^14 cycles per second. Energy = Planck’s Constant * frequency. Planck’s Constant is 6.626*10^-34 joules*seconds.
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- So the energy per photon = 2.05*10^-19 joules. To calculate how many photons are coming off the bulb, 100 joules / second / 2.05*10^-19 joules / photon = 48*10^19 photons per second. No wonder light was thought to be a wave with that many particles per second flowing at you.
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- The emitted power per square meter = Boltzman’s Constant * temperature^4. Boltzman’s Constant = (5.7*10^-8 watts / m^2) * K^4. So, emitted power per square meter = 4,617,000 watts / m^2. Since the bulb puts our 100 watts, the tungsten wire surface are must be 100 / 4,617*10^6 = 0.216 centimeters^2.
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- Heat is thermal energy. Thermal energy is vibrating atoms. Every bit of ordinary matter above the absolute zero temperature of -273 Centigrade has vibrating atoms and therefore some thermal energy.
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- Space is -270 Centigrade, so it is only 3 degrees above absolute zero. Energy and temperature can be calculated with a few simple formulas. E=h*f, E = 6.626*10^-34 * frequency, for the energy of a photon.
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- The energy of light is directly proportional to its frequency. Peak Wavelength = 2,900,000 nm / Kelvin. Peak Wavelength comes from the curve of light intensity versus wavelength for a “ Blackbody” spectrum.
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- A “ Blackbody” is simple a perfect emitter ( or absorber) of light. The curve always has the same shape. Its peak only shifts to occur at a specific wavelength for each temperature. Power density = 5.7*10^-8 * (Kelvin)^4. Light emitter power per square meter increase in direct proportion to the 4th power of its temperature.
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- Well I hope that puts a little more light on it. Understanding light is no easy matter.
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- June 11, 2019. 940
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--------------------- Friday, June 21, 2019 -------------------------
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