chapter 12

what is the term used to describe the total amount of power a star emits into space

luminosity

which law describes how the apparent brightness of a star changes with distance

inverse square law

if a star’s distance from earth is doubled, by what factor does its apparent brightness decrease

4

how do astronomers define the apparent brightness of a star

the amount of power reaching us per unit area from the star

which unit is used to measure stellar luminosity

watts

what is the most direct method for measuring the distance to nearby stars

stellar parallax

what is the parallax angle of a star that is 10 parsecs away

0.1 arcseconds

what distance does one parsec correspond to in light-years

3.26 light-years

how do astronomers use parallax measurements to calculate stellar distances

by comparing observations of stars made six months apart and measuring their apparent shift against distant stars

which property of stars is directly measurable and often used to infer other properties like interior temperature

surface temperature

what relationship between surface temperature and luminosity can be observed from the patterns among stars

hotter stars tend to be more luminous

which astronomers are credited with recognizing the relationships between stellar properties in the early 20th century

ejnar hertzsprung and henry norris russell

what does the horizontal axis of an h-r diagram represent

stellar surface temperature

on an h-r diagram, where would you find hot and luminous stars

upper right

how dies stellar radius change as you move from the lower left to the upper right on an h-r diagram

stellar radii increase

which luminosity class represents supergiants

I

which of the following is a correct classification for a main-sequence star

G2 V

how do stellar masses vary along the main sequence on an h-r diagram

stellar masses decrease downward along the main sequence

why do more massive main-sequence stars have shorter lifetimes than less massive ones

they fuse hydrogen at a much greater rate

what is the most fundamental property of a star that determines its surface temperature and luminosity during its main-sequence phase

mass

what characteristic distinguishes giants and supergiants from main-sequence stars on an h-r diagram

they are cooler but much more luminous than main-sequence stars

why do white dwarfs become dim over time despite being initially hot

they lack an energy source and radiate only their leftover heat into space