- 2680 - ORION NEBULAE - what makes it so amazing? - Most everyone knows the winter night sky’s most popular constellation, “Orion the Hunter“. The 3 dominate stars in the center are Orion’s Belt and just below the Belt is Orion’s Sword, and just below the Sword is the Orion Nebula. This is a spectacular sight with a telescope.
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------------------- 2680 - ORION NEBULAE - what makes it so amazing?
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- The Orion nebulae is a gas cloud of on-going star formation. You can actually see stars being born. It is what our Solar System looked like 4,600,000,000 years ago.
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- Our Milky Way Galaxy has two major spiral arms. The Orion spur is a smaller stream of stars that lie between the Peresus Arm and the Sagittarius Arm. Our Solar System lies 2/3 rds of the way out from the center, 27,000 lightyears.
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- The Orion Nebula lies in the Orion Spur just 1,500 lightyears away. You see the rim of the Milky Way when you look above the Orion Constellation. The rim arcs across the sky. We are looking away from the center in the direction of the Orion Nebula.
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- We would have to follow the arc all the way to the summer sky to see the center of the galaxy. The center is toward the constellations Scorpius the Scorpian northwest of Sagittarius the Tea Pot. We can not see the blazing stars at the center because huge clouds of dust and gas are in the way.
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- Similar gas and dust can be seen in the Orion Nebula. The entire gas cloud surrounding the Nebula is called M42, the Orion Molecular Cloud.
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- The middle star in Orion’s Belt is the Trapezium. Using a telescope you learn that it is actually 4 stars, not just one as it appears with the naked eye. These are young stars, only 300,000 years old. One of the stars is 40 Solar Mass and has a surface temperature of 40,000 Kelvin.
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- These young stars emit huge amounts of ultraviolet radiation. The UV rays cause the hydrogen gas surrounding the stars to fluoresce green in color. The nitrogen gas fluoresces red in color, The oxygen gas fluoresces blue.
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- This middle star is called Theta C in the Trapezium. It shines 210,000 times brighter than our Sun. the stellar wind that it emits travels 5,700,000 miles per hour. Theta C is a massive star, burning its fuel rapidly and will explode in a supernova in about 1,000,000 years.
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- The Orion Nebula is 1,500 lightyears away and is 10 lightyears across. To learn more about the colors in the gas that is condensing into stars we need to learn what goes on inside the atom.
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- A hydrogen atom is a proton in the nucleus surrounded by an electron in orbit about the nucleus. Each orbit is called a shell, or an energy level. The more energy the atom absorbs the higher the energy level the electron occupies.
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- Level 1 is the lowest energy level. When the electron falls from energy level 3 to energy level 2 the loss of energy is released as a red photon at 656 nanometers. When an electron falls from level 2 to level 1 the photons released are in the ultraviolet wavelengths.
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- Not all the colors are emissions of radiation. Some are reflections. When starlight enters a dust cloud the reflected light is blue. Interstellar dust grains scatter blue light much more readily than red light. ( This same scattering in our atmosphere causes the sky to be blue.)
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- When a hydrogen atom exceeds a certain amount of energy absorption it becomes ionized. That is, it loses its electron. The negatively charged electron escapes as a free electron.
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- The nucleus that remains is a positively charged proton nucleus, called an ion. Star formation starts out with a bubble of gas in this high energy state. The gas cools as it emits radiation and in condenses as gravity compresses the mass of gas towards its center.
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- The stages of star formation in the Orion Nebula show cooling and density changes:
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------- Hot bubbles of heated gas are created by supernovae shockwaves:
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--------------------------------------------- temperature ---------------------- density------------
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------- Ionized hydrogen ------------- 1,000,000 Kelvin ------------- 0.01 atoms / cm^3
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------- Warm atomic gas that fills much of the galactic disk:
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------- Atomic hydrogen ------------- 10,000 Kelvin ------------------ 1 atoms / cm^3
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------- Cool atomic clouds as gas condenses to form stars:
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------- Atomic hydrogen ------------- 100 Kelvin --------------------- 100 atoms / cm^3
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------- Molecular clouds that are regions of star formation:
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------- Molecular hydrogen ------------- 30 Kelvin --------------------- 300 atoms / cm^3
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------- Molecular cloud cores that are actively forming stars, fusion begins at the cores.
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------- Molecular hydrogen ------------- 60 Kelvin ------------- 10,000 atoms / cm^3
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- These different gases are identified by the wavelength of their emissions. Each wavelength corresponds to a specific color or frequency of the electromagnetic radiation:
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---------- Single ionized oxygen ------------------ 375 nanometers ------------- Blue
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---------- Double ionized neon -------------------- 400 nanometers ------------- Blue
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---------- Atomic hydrogen ---------------------- 410 nanometers ------------- Blue
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---------- Atomic hydrogen ---------------------- 435 nanometers ------------- Light Blue
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---------- Atomic helium ------------------------- 450 nanometers ------------- Light Blue
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---------- Atomic hydrogen ---------------------- 485 nanometers ------------- Blue Green
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---------- Double ionized oxygen ------------------ 505 nanometers ------------- Green
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- Orion the Hunter offers the backyard astronomer many more discoveries. Near the Orion Molecular Cloud is M43, the Running Man Nebula. Above the Orion Nebula and below the Belt are the Flame Nebula and the famous Horsehead Nebula.
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- Have fun with that new telescope. They even have telescopes that connect to your cell phone.
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- March 26, 2020 1122 2680
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--------------------- Thursday, March 26, 2020 -------------------------
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