Astronomy Unit 3 Flashcards
a measure of the amount of light received by Earth from a star or other object—that is,
how bright an object appears in the sky, as contrasted with its luminosity
apparent brightness
an object intermediate in size between a planet and a star; the approximate mass range is from
about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, which is about 0.075 the mass of the Sun; brown dwarfs are capable of deuterium fusion, but not hydrogen fusion
brown dwarf
difference between the magnitudes of a star or other object measured in light of two different
spectral regions—for example, blue minus visual (B–V) magnitudes
color index
a star of exaggerated size with a large, extended photosphere
giant
the rate at which a star or other object emits electromagnetic energy into space; the total power
output of an object
luminocity
an older system of measuring the amount of light we receive from a star or other luminous object;
the larger the magnitude, the less radiation we receive from the object
magnitude
the angular change per year in the direction of a star as seen from the Sun
proper motion
motion toward or away from the observer; the component of relative velocity that lies in the
line of sight
radial velocity
the total (three-dimensional) speed and direction with which an object is moving through space relative to the Sun
space velocity
(or spectral type) the classification of stars according to their temperatures using the characteristics of their spectra; the types are O, B, A, F, G, K, and M with L, T, and Y added recently for cooler star-like objects that recent survey have revealed
spectral class
two stars that revolve about each other
binary stars
an object intermediate in size between a planet and a star; the approximate mass range is from
about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, which is about 1/12 the mass of the Sun
brown dwarf
a binary star in which the plane of revolution of the two stars is nearly edge-on to our line of
sight, so that the light of one star is periodically diminished by the other passing in front of it
eclipsing binary
(Hertzsprung–Russell diagram) a plot of luminosity against surface temperature (or spectral
type) for a group of stars
H-R diagram
a sequence of stars on the Hertzsprung–Russell diagram, containing the majority of stars, that
runs diagonally from the upper left to the lower right
main sequence
the observed relation between the masses and luminosities of many (90% of all)
stars
mass-luminosity relation
the selection of sample data in a nonrandom way, causing the sample data to be
unrepresentative of the entire data set
selection effect
a binary star in which the components are not resolved but whose binary nature is
indicated by periodic variations in radial velocity, indicating orbital motion
spectroscopic binary
a binary star in which the two components are telescopically resolved
visual binary
a low-mass star that has exhausted most or all of its nuclear fuel and has collapsed to a very small
size; such a star is near its final state of life
white dwarf
a star that belongs to a class of yellow supergiant pulsating stars; these stars vary periodically in
brightness, and the relationship between their periods and luminosities is useful in deriving distances to them
cepheid
a graph that displays the time variation of the light from a variable or eclipsing binary star or, more
generally, from any other object whose radiation output changes with time
light curve
a classification of a star according to its luminosity within a given spectral class; our Sun, a
G2V star, has luminosity class V, for example
luminosity class
an apparent displacement of a nearby star that results from the motion of Earth around the Sun
parallax
