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One of the oldest recorded novae was observed in 1437 by a Korean astronomer. 

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A nova is a star that suddenly increases in brightness, becoming much brighter than it was before.

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All elements heavier than iron were created in supernova explosions. 

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A supernova remnant is the structure left behind after a star explodes in a supernova

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White dwarfs have a surface gravity that's 350,000 times stronger than Earth's gravity

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A white dwarf is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula.

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A supernova occurs in the universe every 10 seconds, but the Milky Way only experiences about two per century.

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A supernova is a massive explosion that occurs when a star dies

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Diffuse nebulae are made up of mostly hydrogen, with smaller amounts of helium, oxygen, sulfur, and other heavier elements.

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Are the clouds of material formed from the explosions of population three, population two stars, and the left over hydrogen and helium from the Big Bang.

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Supergiants have a shorter lifespan than main sequence stars, lasting only 10 to 50 million years. 

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Super giants are among the most massive and most luminous stars.

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Black holes don't emit or reflect light, so they are invisible to the human eye.

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a region of space having a gravitational field so intense that no matter or radiation can escape.

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Depending on their temperature, main sequence stars can appear blue, white, yellow, orange, or red. 

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A main sequence star is any star that has a hot, dense core which fuses hydrogen into helium to produce energy.

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Planetary nebulae are short-lived, lasting only a few thousand to tens of thousands of years.

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A planetary nebula is a cloud of gas and dust that forms when a star dies and sheds its outer layers.

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Red giants appear red or orangish because of their relatively cool surface temperatures.

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A giant star has a larger radius and luminosity than a main-sequence star of the same surface temperature.

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Our sun is located in the middle of the diagram.

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HR Diagram is a scatter plot of stars showing the relationship between the stars' luminosities and their effective temperatures.

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The Boomerang Nebula is the coolest natural place in the universe.

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Nebulae are interstellar clouds of gas and dust.