Galaxies and StarsWhat does our galaxy look like and what

types of stars exist inside?

• Galaxy - a collection of billions of stars and various amounts of gas held together by gravity

•Average galaxies have around 100 billion stars

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• Galaxies have been classified by the following shapes:

Elliptical SpiralIrregular

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• Milky Way Galaxy - our solar system is part of a spiral shaped galaxy with 200 billion stars

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• Star - large ball of gas held together by gravity that produces tremendous amounts of energy and shines

•Make up the majority of known matter in the galaxy

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Solar Flares

•Nuclear Fusion - the combining of smaller elements to form the nuclei of larger elements

•The Sun converts hydrogen nuclei into helium nuclei

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•Luminosity - a measure on how bright a star is compared to our Sun

• Luminosity and temperature are used in classifying the different types of stars on a H-R Diagram

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Luminosities

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Earth Science Reference Tables

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• Stars have a life cycle and undergo stellar evolution

• Stars originate from a cloud of dust and gases

•Gravity causes them to clump together and form larger balls of dust and gases

•When gravitational contraction creates enough heat they ignite and start nuclear fusion

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• Main Sequence Star - average size, temperature, and luminosity stars

• 90% of the known stars spend their life on the main sequence

•The Sun is apart of the main sequence

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• Red Giant Stars - a luminous easily seen star that is in a late phase of stellar evolution

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• Super Giant Stars - star with an extremely high temperatures in the late stages of its stellar evolution

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• White Dwarf Stars - Earth sized star with a low luminosity and a hot surface

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Galaxies and Stars