- 3227 - CEPHEID’S - Used to Discover America? Cepheid’s are stars that pulsate, varying their brightness in a cyclic manner. Edwin Hubble found a Cepheid star in the Andromeda Nebula in 1923. That was the first time astronomers realized that Andromeda was another distant galaxy, (M31) and not a nebula, or gas cloud, in our Milky Way Galaxy. Up until 1923 all astronomy was limited to inside the Milky Way Galaxy
------------------ 3227 - CEPHEID’S - Used to Discover America?
- How our Universe has changed in the last 100 years.
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- Columbus sailed the Atlantic Ocean in 1492 with uncanny ability to do naked eye fixes on the North Star. The North Star is ‘Polaris” at the tip of the handle of the Little Dipper. By keeping the altitude of Polaris fixed in the night sky Columbus kept his expedition on course to within one degree of latitude.
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- Polaris is a Cepheid star that everyone knows as the North Star.
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- Polaris is only 430 lightyears away. Like all Cepheids Polaris varies in brightness over a given time period, about 4 days for Polaris.
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- Astronomers have learned that they can deduce a Cepheid’s luminosity based on the duration, or period of the cyclic brightness changes. Then by comparing the luminosity of the observed brightness to the actual brightness when it left the star they can determine the distance to the Cepheid. In this case 430 lightyears distance. The dimmer the Cepheid star the further away it is.
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- Cepheids pulsate due to a very defined process causing them to shrink and expand varying their surface temperature and brightness. Cepheid pulsations can have cyclical durations from 1 o 100 days. Cepheid stars live for only 60 million years but they shine 500 to 30,000 times brighter than our Sun. This extreme brightness allows astronomers to see them over great distances.
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- Here is the physics causing Cepheids to pulsate:
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-------------- Cepheids are special stars that contain a layer of helium at just the right temperature and pressure to undergo this cyclic pulsation:
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------------ Helium atoms in the pulsating layer are singly ionized, lost one electron and have a net He+1 charge. Singly ionized helium atoms are transparent to light radiation so light energy passes through the layer.
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--------------- Helium atoms absorb some of the energy and get hotter. The atoms lose their second electron and become doubly ionized, He+2 charge. Doubly ionized helium is opaque to light , blocking the light, acting as a dam, lifting the layer, expanding the star’s radius.
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------------- The expansion reduces the pressure and temperature allowing helium atoms to gradually capture electrons and revert back to singly ionized atoms, He+1. The layer is transparent again releasing the energy stored below the pulsation layer.
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---------------- With the pressure released the pulsation layer contracts. The He+1 begins to absorb energy again and the cycle starts all over again.
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- Supernovae Type 1A are exploding stars that have a standard light curve of luminosity. Supernovae are much, much brighter than Cepheids. Astronomers can see supernovae at billions of lightyears distance.
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- Astronomers find a nearby galaxy that has both supernovae and Cepheids. They calculate the distance to the pulsating Cepheids and since they are in the same galaxy as the supernova they know the distance that corresponds to the supernova brightness light curve. Astronomers can then use the brightness / distance ratio to calculate the distance to those far off supernova having the same light curve.
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- Cepheid luminosity varies through a cycle, where the color ( temperature) and radius change:
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--------------------- pale yellow ---------- maximum luminosity
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--------------------- yellow ----------------
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-------------------- orange -----------------minimum luminosity
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------------------- yellow -----------------
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-------------------- pale yellow ------------ maximum luminosity
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- The duration of this cycle can be used to determine the luminosity:
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------------------ Period -------------------------- Brightness ( times our Sun )
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------------------ 2 days -------------------------- 500
------------------ 3 days -------------------------- 1,000
------------------ 5 days -------------------------- 1,200
------------------ 10 days -------------------------- 5,000
------------------ 30 days -------------------------- 10,000
------------------ 50 days -------------------------- 30,000
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- Using this data astronomers have calculated that the galaxies are moving away from each other in an expanding Universe at 74.2 kilometers per second per mega parsec. A mega parsec is 3.26 million lightyears. 72 km / sec is 161,000 miles per hour, or:
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----------------- 47,000 miles per hour per million lightyears
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---------------- For every million lightyears distance you look the galaxy is receding at a velocity of 47,000 miles per hour.
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---------------- If a Cepheid is in a galaxy 1 billion lightyears away, it is traveling away from us at 47,000,000 miles per hour. Light travels at 670,000,000 miles per hour, so that is 7% the speed of light.
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- When astronomers look far enough away the galaxy is moving at 100% the speed of light and the light will never reach us. The galaxy goes beyond the Observable Universe.
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- Remember the galaxy is not speeding, the space between us and the galaxy is expanding. That is why receding galaxies can exceed the light speed barrier. The light speed barrier applies to mass not to the vacuum of space.
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- July 22, 2021 CEPHEID’S - Used to Discover America? 1055 3224
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--------------------- --- Saturday, July 24, 2021 ---------------------------
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