Light Spectrum, how we know about the stars?

--------- #1335 - Light Spectrum

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- Light is electromagnetic radiation that is emitted and absorbed by matter. Specifically by electrons up through ultraviolet light and by the nuclei of atoms in X-rays and Gamma Rays. It was in 1666 that Isaac Newton discovered the spectrum of sunlight using a prism.

- In 1802 the absorption lines were first discovered in the spectrum. Absorption lines are dark lines in the spectrum where frequencies are missing. In 1814 astronomers first used a spectra with a telescope. In 1835 science began to identify specific elements associated with specific absorption lines and emission lines found in spectra.

- In 1873 Maxwell’s equations first published the theory behind electromagnetic forces and the theory that light was an electromagnetic wave. In 1913 Neil’s 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.

- 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 the exact energy level when the electrons drop back down to their lower energy levels.

- 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. Wien’s law is that the maximum wavelength of the source is approximately equal to 2,900,000 nanometers / temperature in Kelvin. Then, Stefan-Boltzmann’ s law states that the emitted power per square meter of surface area = (5.7*10^-8 ) * (temperature in Kelvin)^4. Power is proportional to temperature raised to the 4^th power.

- 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. 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. The wavelength of radiation / (speed of light) = (the shift in wavelength) - (wavelength if measured at rest) / (wavelength if measured at rest). For example: 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.

- 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. 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.

- 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. 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.

- 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.

- 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. 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. 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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