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Explosive solar ‣‣‣flares are caused when the magnetic field lines break These solar flares can cause huge amounts of gas to be ejected in a Coronal Mass Ejection When Coronal Mass Ejections hit Earth ‣‣they can disrupt communications and cause beautiful aurorae‣How do we measure stellar distances? Parallax tells us distances to the nearest stars How do we measure stellar luminosities? If we measure a star’s apparent brightness and distance, ‣‣‣we can compute its luminosity with the inverse square law for light How do we measure stellar masses? Newton’s version of Kepler’s third law tells us the total mass of a binary system, if ‣‣we can measure the orbital period (p) and average orbital separation of the system (a)What are the three basic types of spectra? Continuous spectrum, emission line spectrum, absorption line spectrum How does the Sun’s spectrum tell us about its composition? Each ele‣‣‣-ment has a unique spectrum line “fingerprint” We can determine which elements the Sun is made of by looking for their fingerprints in its spectrum How do we measure stellar tempera‣‣-tures? A star’s color and spectral type both reflect its temperature‣What is the relationship between luminosity, temperature, and size? For stars of the same size, the hotter one has greater luminosity For stars of the same temperature, the larger star has ‣‣greater the luminosity What is a Hertzsprung-Russell diagram? An H-R diagram plots luminosity of stars versus surface temperature (or color or spectral type) 90% of stars are on main ‣‣‣sequence Cool and luminous stars are called red giants Dim but hot stars are called white dwarfs‣‣What is the significance of the main sequence? Normal stars that fuse H to He in their cores fall on the main sequence of an H-R diagram A star’s mass determines its position along the ‣‣main sequence (high-mass: luminous and blue; low-mass: faint and red) What is the average star like? 70% of nearby stars are red dwarfs, < 0.5 MSun Massive main sequence stars and ‣‣‣red giants are rare