Study GuideAstronomy–The Milky Way Galaxy1. Origin and EvoluƟon of the GalaxyAstronomers study theorigin and evolution of the Galaxyby observing where stars are located,how they move, and what they are made of. These observations reveal clues aboutwhen and howdifferent stars formed.Early studies showed that stars in the Galaxy could be grouped based on their age, location, motion,and chemical composition. These groups are calledstellar populations.1.1Stellar PopulaƟons: An OverviewOriginally, astronomers identifiedtwo main stellar populationsbecause their properties were verydifferent. Later, a third population was discovered.The main populations are:•Population I•Population II•Population III(the earliest stars)Each population helps us understand a different stage in the Galaxy’s history.1.2 PopulaƟon I Stars–Young and Metal-RichPopulation I stars are theyoungest stars in the Galaxy.Their key features include:•Found mainly in thegalactic disk•Often located inopen clusters and stellar associations•Containbright, blue O and B stars•Closely associated withgas and dust, from which they recently formed•Havechemical compositions similar to the Sun•Heavy element content ranges fromone-third to twice the solar abundance•Move withsmall velocities relative to the SunThese stars are still forming today in the thin disk of the Galaxy.Preview Mode
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