30.1 Characteristics of Stars Stars Characteristics of Stars · star = ball of gas that emits light Section 30.1 · fueled by nuclear fusion · vary in color Analyzing Starlight Star Characteristics · spectrographs - device that separates light into · composition different wavelengths (colors) most common element - hydrogen · each star produces a unique spectrum (series of second most common - helium colors and lines) · temperature · a star's spectrum tells us blue = hottest elements present (composition) yellow (ex. sun) surface temperature red = coolest how fast the star is moving · size and mass toward or away from Earth dwarf, medium, and giant Solar spectrum 1 How do scientists determine the 2 What color are the warmest stars? composition and temperature of stars? A yellow A by taking samples from the star's surface B blue B by analyzing the vibrations that the star emits C white C through magnetic testing D red by analyzing the spectra of the light that a D star emits 30.1 Characteristics of Stars Stellar Motion · apparent motion visible to the unaided eye caused by Earth's rotation appear to move counter-clockwise around Polaris (the North Star) different stars appear in different seasons Red Shift = star moving away circumpolar stars - always visible in the night sky · actual rotate on an axis revolve around another star move away from or toward our solar system · Doppler effect shifting wavelengths of light emitted by a light source moving toward or away from an observer Blue shift = star moving toward blue shift = moving toward Earth red shift = moving away from Earth Distances to Stars Stellar Brightness · light-year = distance light travels in one year · visibility of a star depends on brightness (magnitude) 9.46 trillion km/year and distance from Earth sun = 8 light minutes away 1 = brightness stars Proxima Centauri = 4.2 light-years away 6 = faintest stars Polaris = 700 light-years away · apparent magnitude = brightness of a star from · parallax = apparent shift in a star's Earth position when viewed from · absolute magnitude = how bright a star would be if different locations it were 32.6light-years from Earth accurate up to 1000 aka true brightness light-years compared against a standard 3 Why do stars appear to move in the 4 Scientists use parallax to determine sky? A a star's distance A the sky is rotating B if the star is moving toward or away from Earth B the universe is expanding C the brightness of a star C Earth is moving D a star's actual motion D galaxies are forming.