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--------------------- 2427 - ASTRONOMY - A New Astronomy
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- For 3 million years our ancestors had only the naked eye to view the heavens. These first astronomers were still able to contemplate the 5 planets, the Moon, the stars in the Milky Way and even Andromeda our neighboring galaxy.
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- It was only 400 years ago that astronomy changed with the invention of the telescope, in 1609 by Galileo. Suddenly new horizons were visible with higher resolution for the human eye.
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- By 1929 telescopes had grown to 200 inches in diameter and Edwin Hubble used the first one to discover galaxies. He learned that the further away a galaxy was the faster it was receding. Therefore the Universe was expanding.
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- The visible light spectrum is only a very small part of the electromagnetic radiation spectrum. It is only 400 to 700 nanometers in wavelengths from blue to red light. Astronomers soon realized that there was radiation above the red into the infrared and beyond the blue into the ultraviolet.
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- The infrared is essentially heat radiation and spans from 700 to 450,000 nanometers wavelength. Ultraviolet are the wavelengths of 90 to 350 nanometers. Ultraviolet astronomy, starting in 1946, is used to study chemical compositions, densities, and temperatures of interstellar gas and dust and the birth of young stars. In 1962 the first satellite made ultraviolet measurements.
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- Spectroscopy actually started in 1666 with Isaac Newton passing a light through a glass prism. In 1857 Kirchhoff and Bunsen began identifying the chemical element’s signatures in the spread spectrum. Astronomers use this same technique to identify the elements in the light from stars.
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- When elements in spectra are redshifted, shifted toward the red end, longer wavelength, of the spectrum the velocity of recession can be calculated. Using the Hubble constant astronomers can then estimate the distance to the source star.
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- Beginning with WWII astronomers realized that there was much more beyond the spectrum of light that could be used in the study of astronomy. In 1938 the first discoveries were made using radio astronomy. In 1946 higher resolution was made possible by a new technology using radio interferometers. These tools were used to discover pulsars, quasars, and radio galaxies.
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- Recently this technology has been used to measure the rotation of galaxies and to discover the magnitude of Dark Matter. Because the rotational velocities remained constant for stars orbiting far out from the center of the galaxy there had to be a missing mass far greater than that emitting visible light. They determined that Dark Matter, whatever it is, comprises 90% of all the matter in the Universe.
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- In 1949 cosmic X-rays were discovered. The Chandra X-ray satellite was launched in 1999 advancing the study of neutron stars and black holes. Black Holes emit X-rays at their accretion disks, just beyond the event horizon, when in falling gas reaches enormous temperatures.
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- In 1960 gamma rays were first detected in space. Gamma ray satellites are being used to study large supernova explosions that create black holes.
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- In 1965 the Cosmic Microwave Background radiation was discovered in the microwave part of the spectrum, at 1.4 Ghz, equivalent to a temperature of 2.7 degrees Kelvin. The CMB is a blackbody radiation that covers a wide spectrum of frequencies, up to 160.4 Ghz, or a wavelength of 1,900,000 nanometers..
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- Satellites detected polarization at the level of a few micro Kelvin in this radiation. This has opened up a new dimension in the study of CMB astronomy.
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- In 1949 polarization of light was first discovered in astronomy. When starlight travels through interstellar dust its scattering becomes polarized. Astronomers have recently used polarization to determine the shape of exploding Type 1a supernova which are the “standard candles” used to determine the distance of far away galaxies.
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- The supernova explosion starts out clumpy and uneven until it is over come by a second, spherical blast that overwhelms the first creating a smooth residue. The shape of the blast sets the limits of uncertainty on the distance measurements astronomers make using the brightness light curve.
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- Electromagnetic waves oscillate in certain directions. Reflections or scattering of light favors certain orientations of the electric and magnetic waves. When light scatters through the exploding debris of a supernova it retains information about the scattering layers.
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- These observed polarization phenomena are analogous to explosions in the internal combustion engines of cars. The clumpiness is caused by “deflagration”, a slow burn with turbulence. The smoothness occurs when “detonation”, traveling at super sonic speeds, overcomes the “deflagration” stage and creates a smooth burn.
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- In 1952, as part of radio astronomy, the first maps were made of our own Milky Way Galaxy. The signals being detected were from the radiation of neutral hydrogen. A hydrogen atom is a single proton and a single electron. Both have properties of spin . Any spinning charged particle has magnetic interactions.
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- If the proton and electron are spinning clockwise, in the same direction, they have slightly more energy together then if the electron and proton are spinning in opposite directions. If the spin reverses the excess energy is released with photons at 21 centimeter wavelengths, exactly 1.42040575 Megahertz frequency . When this frequency is redshifted coming from a distant source that is receding, it is detected on Earth at the radio frequencies between 200 and 9 Megahertz.
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---------------------- Frequency = speed of light / wavelength
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---------- Frequency = 2.998*10^10 cm/sec / 21 cm = 1.427 * 10^9 cycles per second
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- In 2005 this 21 centimeter astronomy was used to detect the first Dark Galaxy. This galaxy, Virgo HI21, located in the constellation Virgo, consists of hydrogen gas and Dark Matter and no visible, or detectable stars. With 21 centimeter astronomy it was determined that the galaxy was 52 million lightyears across, 200 million solar mass, or about 10% the size of the hydrogen mass in the Milky Way.
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- The hydrogen atoms in this galaxy have orbital velocities of 500,000 miles per hour. In order to keep these high speed atoms from escaping the gravitational mass must be greater than 90,000 million solar mass. This would mean that 97% of the galaxy was composed of undetected Dark Matter. It is hoped that further study of this galaxy might give us some insight of what Dark Matter really is.
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- 21 centimeter astronomy is only possible because the Universe is filled with lots of hydrogen. If left alone a hydrogen atom has an extremely low probability of reversing electron spin and releasing this energy. It is 2.9 * 10^-15 events / second. That translates to one event every 10 million years. However, there is so much hydrogen out there that 21 centimeter radiation is easy to find using modern radio telescopes.
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- The new astronomy keeps coming up with new ways to study the Universe using the information in electromagnetic radiation. Astronomers today are not limited to electromagnetic photons. Use is being made of neutrinos and gravitons, gravity waves, to make new discoveries in the Universe. Who knows what they will think of next?
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- Stay tuned , there is much more to learn.
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- August 2, 2019. 714
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--------------------- Friday, August 2, 2019 -------------------------
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