- 3073 - LIGHT - Light Spectrum discovered? Light is radiation that is emitted and absorbed by matter. Light is electromagnetic radiation because it is a combination of electric waves and magnetic waves that travel at high speeds oriented perpendicular to each other.
--------------- 3073 - LIGHT - Light Spectrum discovered?
- Light radiation is absorbed and emitted by electrons up through ultraviolet light and by the nuclei of atoms in X-rays and Gamma Rays.
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- It was in 1666 that Isaac Newton discovered the spectrum of sunlight using a prism. Sunlight was spread into a rainbow of blue to red colored light.
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- In 1802 the first discovery of absorption lines were discovered in the light spectrum. Absorption lines are dark lines in the spectrum where frequencies are missing. In 1814 astronomers first used a spectra with a telescope.
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- In 1835 science began to identify specific elements associated with specific absorption lines and emission lines found in spectra.
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- In 1873 Maxwell’s equations first published the theory behind electromagnetic forces and the theory that light was an electromagnetic wave.
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- In 1913 Niels Bohr published the theory of electrons occupying discrete energy levels in the atom orbiting about the nucleus. His theory allowed the absorption and emission lines for specific elements to exactly match the calculations for discrete energy levels in the electron orbits.
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- When atoms absorb energy ( light) the electrons jump from a lower energy level to a higher energy level. Energy always seeks it lowest energy level. So, atoms emit this exact energy level when the electrons drop back down to their lower energy levels.
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- When astronomers studied the spectrum of light coming from different objects in the Cosmos they could identify what elements were present at the source of the radiation. The frequency of the emissions also told astronomers the surface temperature of the source.
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- Wien’s law is that the maximum wavelength of the source is approximately = 2,900,000 nanometers / temperature in Kelvin.
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- For example: The wavelength where sunlight is maximum intensity is 500 nanometers. This wavelength is visible light that is yellowish - green in color. The blue wavelengths in sunlight gets scattered by our atmosphere and we see a yellow Sun in a blue sky.
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------------------ 500 nanometers = 2,900,000 nanometers / Temperature
----------------- Temperature = 5,800 degrees Kelvin
- A bright blue star has a peak wavelength at 193 nanometers. Its temperature is 2,900,000 / 193 = 15,000 degrees Kelvin for a surface temperature. 193 nanometers is in the ultraviolet part of the spectrum. We see the less intense visible blue wavelengths.
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- Then, Stefan-Boltzmann’ s law states that the emitted power per square meter of surface area = (5.7*10^-8 ) * ( temperature in Kelvin)^4.
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- For example: The power emitted by a star goes as the for the power of its surface temperature.
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--------------------------- Power emitted = (5.7*10^-8) * T^4
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--------------------------- Power emitted = (5.7*10^-8) * (15,000)^4
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--------------------------- Power emitted = 2,900,000,000 watts / square meter
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- Our Sun emits 62,400,000 watts / meter^2. We receive about 1,300 watts per square meter on the surface of the Earth.
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- If the spectrum is spread out, made broader, that indicates the presence of a magnetic field at the source. Spectrum also indicates if the source is coming towards us or away from us and how fast.
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- It is the Doppler Effect with a “blue shift” indicating a velocity towards us. A “redshift” indicating a velocity away from us. The percentage of the shift indicates the magnitude of the velocity.
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- The wavelength of radiation / speed of light = the shift in wavelength - wavelength if measured at rest / wavelength if measured at rest.
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- In 1962 astronomers measured the spectral shift of hydrogen lines at 16% indicating that distant Quasars were moving away from us at 16% the speed of light.
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- For example: The hydrogen atom absorption line in the spectrum from the Star Vega is shifted to 656.255 nanometers from 656.285 nanometers emitted at the source. The percentage of shift is small because the velocity compared to the speed of light is small.
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----------------------- 0.03 nanometers / 656.285 nm = 0.00457% of the speed of light.
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----------------------- 0.00457 % of “c” = 13.7 kilometers per second,
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- Or 30,647 miles per hour which is the typical velocity for stars in our neighborhood. It is negative in the formula because the velocity of Vega is coming towards us. It is blue shifted.
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- In 1800 William Herschel discovered infrared radiation at the edge of the spectrum of red light. In 1983 we launched the first infrared telescope discovering 350,000 energy sources in the Cosmos emitting infrared light.
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- We had to wait that long to get above the atmosphere that absorbs this infrared radiation before it reaches the ground. In 1801 Herschel discovered ultraviolet light at the opposite edge of the spectrum of blue light.
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- In 1887 Hertz discovered the radio waves portion of the electromagnetic spectrum. In 1933 Jansky discovered radio waves coming from the center of the Milky Way Galaxy.
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- In 1942 radio waves were discovered coming from the Sun. In 1946 radio waves were discovered coming from Cygnus A which became the first extragalactic radio source to be identified. Since then radio astronomers have discovered Pulsars, Quasars, and the Cosmic Microwave Background radiation.
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- The newest spectrum being used in astronomy are X-rays and Gamma Rays. Each new part of the electromagnetic spectrum offers astronomers a whole new field of study.
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- For example: Quasar APM 08279+5255 resides 12 billion lightyears away from us. It was found to contain the biggest reservoir of water known in the entire Universe. It has 140 trillion times the water in all the Earth’s oceans. This water vapor surrounds the Quasar for hundreds of lightyears distance.
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- The water is relatively warm at -53 Celsius, compared to the surrounding background space at -270 Celsius. However, the water vapor is so spread out over this vast volume that it is 300 trillion times less dense than that found in our atmosphere.
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- The Quasar’s Blackhole is 20 billion Solar Mass. This is an amazing water hole in the vast Cosmos. Who would have thought it?
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March 4, 2021 LIGHT - Light Spectrum discovered? 1335 3073
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--------------------- --- Thursday, March 4, 2021 ---------------------------
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