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18 terms

VOCAB ch. 8 The HR Diagram

ch. 8 The HR Diagram
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HR Diagram
a plot of luminostiy against temp (or spectral class) for a group of stars
flux
the amount of energy per second per unit area recieved from a star
luminostiy
how bright a star is
inverse square law
flux=luminosity/area of sphere
parallax
apparent shift in position of object when viewed from 2 points
arcsecond
1/60 of an arcminute
arcminute
1/60 of one degree
parsec
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