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Transcript
Characteristics of Stars 19.1 Basics • Star = body of gas • Gives off heat & light • Vary in size, color, composition, temperature & brightness Composition & Texture • • • • Spectrometer: separates light into colors Each element has unique spectra Most stars are made of H, He, Fe, Na, Ca Color indicates surface temp of star: – Blue = hotter (30,000 C) – Red = cooler (3,500 C) Motion • Apparent motion id due to earth’s movement • Circumpolar stars appear to move around the north star (Polaris) Distances • Light travels ~ 10 trillion km/yr • Proxima centauri is the nearest star at 4.3 l.y. away • Sirius is brightest star at 9 l.y. away • Polaris is 700 l.y. away • Andromeda Galaxy is 2.5 million l.y. away • Parallax Magnitudes • 6000 stars are observable to unaided eye • 3 billion stars can be seen with ground based telescopes Apparent magnitude • Brightness of a star as it appears from earth • Brightest stars have lowest #s • Dimmest stars have highest #s Absolute magnitude • True brightness as stars would appear if seen from 32.5 l.y. from earth Classification • H-R diagram • Absolute magnitude vs. temperature • For most stars the brightness increases as surface temp increases • Main sequence stars are band in center
