Chapter 13 Astronomy Key Terms

binary stars

two or more stars in orbit around each other, held together by mutual gravity

dwarf

small, dim star

eclipsing binary

binary star pair where one periodically passes in front of the other, totally/partially blocking background star from Earth's view

giant

star of larger radius and high luminosity

HR diagram

graph on which stars are located according to temp & luminosity

inverse square law

apparent brightness of body decreases inversely as square of its distance

luminosity

amount of energy radiated per second by a body

magnitude

scale for measuring stellar brightness

main sequence

Region in HR diagram in which most stars, including the sun, are located

mass-luminosity relation

relation between mass and luminosity of main sequence stars

parallax

shift in an object's position caused by observer's motion

parsec

unit of distance equal to 3.26 light years (3.09 \times 10^{13} km), the distance at which an observer sees the max angle between the sun & Earth to be one arc second

proper motion

shift of star's position on celestial sphere, motion perpendicular to the line of sight

radial velocity

velocity of body along the line of sight

red giant

cool, luminous star whose radius is much larger than the sun's

spectral type

indicator of star's temp based on appearance of spectrum lines: O, B, A, F, G, K, M

spectroscopic binary

type of binary star in which spectrum lines exhibit changing Doppler shift as result of orbital motion of one star around the other

standard candle

type of star in which the luminosity has a known value, allowing its distance to be determined by measuring its apparent brightness & applying the inverse square law

triangulation

method for measuring distances

visual binary star

pair of stars held together by their mutual gravity, in orbit about each other, that can be seen with a telescope as separate objects

white dwarf

dense star whose radius is about the same as earth & whose mass is comparable with the sun's

Wien's law

relation between temp & wavelength at which it emits radiation most intensely