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ch. 8 The HR Diagram

HR Diagram

a plot of luminostiy against temp (or spectral class) for a group of stars


the amount of energy per second per unit area recieved from a star


how bright a star is

inverse square law

flux=luminosity/area of sphere


apparent shift in position of object when viewed from 2 points


1/60 of an arcminute


1/60 of one degree


parallax secons, 3.262 lightyears

apparent magnitude

apparent brightness of a star, expressed using the magnitude scale

absolute magnitude

apparent magnitude a star would have if placed at standard distance 10 parsecs from earth

distance moudulus

difference between apparent and absolute magnitude. equivilent to distance by the inverse-square law

main sequence

bulk of stars

white dwarf

below main sequence, hot but dim

red giant

above main sequence, bright but cool

red dwarf

small, cool, faint star, lower right end of the HR diagram

luminosity class

groups stars according to the width of their spectral lines (giants vs. dwarfs)

selection effect

observational bias in which a measured property of a collection of objects is due to the way in which the easurement was made, rather than being intrinsic to the objects themselves

spectroscopic parallax

mthod of determining the distance to a star by measuring its temp and then determining its absolute and apparent brightness of the star's distance from earth

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