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For a few thousand years, people have been gazing at the sky searching for answers to life's big questions. People have always wondered the universe, and the stars seemed very promising as a way of understanding it. Stars can be seen from anywhere on Earth so they were assumed to be everywhere in the universe. This is because stars are powered by nuclear fusion for their energy which transforms hydrogen into helium according to Einstein's famous equation E=mc2. This natural process is fueled by light which causes nuclear reactions right after it bounces off of atoms in its path. The amount of energy released is the same amount that was absorbed into the star. The star then ejects the amount of energy that was produced into space according to Einstein's equation E = m c 2. While this is happening inside the star, some of it is emitted directly into space either in visible light or in infrared light. This is due to certain wavelengths being absorbed by atoms on the outside, while others are emitted on the other side of them which can escape freely to be seen by us. The challenge with determining these things about stars is that they are so far away and very big, so they appear to be mostly white, making them difficult for instruments at Earth to see clearly using visible light. Stars that are closer to us (such as the Sun) are bigger and brighter, but appear mostly white. Stars that are further away (such as Rigel, Betelgeuse, and Sirius B) appear almost black because there is no atmosphere on their surfaces to scatter light waves like air does. It was thought for many years that stars emitted only radiant energy (photons) which means light alone. But this doesn't make any sense because other types of radiation can exist too. For example, radio waves can exist too since radio waves can be detected on the Earth's surface by small antennas that pick up these signals. This is called electromagnetic radiation which includes light, radio waves, microwaves, and x-rays. It was thought that since we can see these things in separate forms it must mean that stars emit these forms of radiation too. The word spectrum means a display or representation of a range of spectral colors (like red is positioned in the middle and the rest is represented by wavelengths on either side of it). This word was originally coined in 1789 by Swedish scientist Anders Johan Lexell when he noticed dark lines in the sun's light when viewed through a prism. He named these dark lines a spectrum. It was later discovered that when other objects are heated to incandescence by heat, they give off light in the form of dark lines too. The first person to realize that other objects in space other than the sun were emitting light, was Father Angelo Secchi who began his astronomical career in 1853. He noticed spectral lines while looking at nebulae through a prism at the observatory of the Roman College of Rome . Secchi was actually attempting to prove that these nebulae were gaseous and not solid objects. cfa1e77820
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