Chapter 19

Which of the following stars is a Cepheid variable? a. Sirius b. Betelgeuse c. Rigel d. Mizar e. Polaris

Polaris

The period-luminosity relationship for Cepheid variables was discovered by a. John Goodricke b. Henrietta Leavitt c. Edward Pickering d. Henry Norris Russell e. Annie Cannon

b. Henrietta Leavitt

How did Henrietta Leavitt "calibrate" her period-luminosity relationship for Cepheid variable stars? In other words, how did she make the general idea into a numerical rule? a. by finding cepheids in star clusters whose distance was known in another way b. because the star closest to us is a Cepheid variable and we know its distance c. by noting that the period was related to the luminosity in all stars d. by measuring the Doppler shift in the spectral lines of Cepheids as they pulsated e. by assuming that the Cepheids that appeared the brightest in the sky were closest to us

by finding cepheids in star clusters whose distance was known in another way

If an astronomer wants to find the distance to a star that is not variable and is located too far away for parallax measurements, she can: a. use the star's light curve b. find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram c. use Kepler's laws as modified by Newton d. search for planets around the star since it is much easier to get the distance to planets e. only throw up her hands in desperation; there is no way to even estimate the distance to such a star

find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram

Astronomers must often know the distance to a star before they can fully understand its characteristics. Which of the following properties of a star typically requires a knowledge of distance before it can be determined? a. its luminosity b. its radial velocity c. its temperature d. its apparent brightness e. all of the above

its luminosity

To get the distance to a Cepheid variable star, astronomers must take several steps. Which of the following is NOT one of these steps? a. observe the star getting brighter and dimmer to establish that it varies b. measure the period of variations by timing when the star is brightest and dimmest c. estimate the apparent brightness of the star d. measure the star's Doppler shift from its spectrum e. apply the period-luminosity relationship

measure the star's Doppler shift from its spectrum

An astronomer is observing a single star (and one which does not vary) which she knows is located about 30 light-years away. What was the most likely method she or her colleagues used to obtain that distance? a. bouncing radar beams off the star b. measuring the star's parallax c. the period-luminosity relationship d. Kepler's laws e. Hubble's law

measuring the star's parallax

An astronomer is interested in a galaxy called M31, the nearest galaxy that resembles our Milky Way. It is about 2 million lightyears away. Which technique would be able to give us a distance to this galaxy? a. parallax b. radar reflections c. period-luminosity relation for Cepheid variables d. Kepler's laws e. you can't fool me: there is no way at present to get a distance to an object so far away

period-luminosity relation for Cepheid variables

Which type of star has the least amount of pressure in its atmosphere? a. main sequence stars b. subgiants c. giants d. supergiants e. you can't fool me; all stars have roughly the same pressure

supergiants

A type of star that has turned out to be extremely useful for measuring distances is a. the eclipsing binaries b. the Cepheid variables c. the main sequence stars d. the white dwarf stars e. the stars that lie in the constellation of Orion

the Cepheid variables

Why do Cepheid variables have that strange name? a. they were discovered by an astronomer named George Cepheid b. the first star discovered to be this kind of variable had the Latin name Cepheidus c. the word Cepheid means changing in brightness in ancient Greek d. the first such variable was discovered in a constellation called Cepheus e. the astronomer who discovered them had a dog named Ceffie

the first such variable was discovered in a constellation called Cepheus

The measurement of cosmic distances was helped tremendously by the discovery, in the early part of the 20th century, that in Cepheid variable stars, the average luminosity was related to: a. their radial velocity b. the abundance of hydrogen in their atmospheres c. their distance from the Sun d. the length of time they took to vary e. their parallax

the length of time they took to vary

The higher the luminosity (intrinsic brightness) a Cepheid variable is, a. the smaller its mass b. the lower it is on the main sequence of the H-R diagram c. the longer the period of its variations d. the closer it is to us e. the larger the telescope we need to observe it

the longer the period of its variations

How do astronomers know that pulsating variable stars are actually expanding and contracting in diameter? a. it is clear just by looking at the light curve b. they discover this by looking at an H-R diagram c. they can measure a regularly varying Doppler shift in the spectral lines d. they can measure the star's changing pull on a companion star around it e. astronomers are just guessing; at the distances of the stars, there is no way to show that stars are expanding and contracting

they can measure a regularly varying Doppler shift in the spectral lines

light curve for a star measures how its brightness changes with a. time b. distance c. mass d. radial velocity e. age

time

The luminosity class of a star tells an astronomer a. whether the star is close to us or far away b. whether or not the star is surrounded by planets c. whether the star is a supergiant, a giant, or a main-sequence star d. how long ago the star formed e. none of the above

whether the star is a supergiant, a giant, or a main-sequence star