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