Astronomy Chapter 19 - 19.3
The period-luminosity relationship for Cepheid variables was discovered by
Henrietta Leavitt
Which of the following stars is a Cepheid variable?
Polaris
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?
by finding cepheids in star clusters whose distance was known in another way
To get the distance to a Cepheid variable star, astronomers must take several steps. Which of the following is NOT one of these steps?
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?
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?
period-luminosity relation for Cepheid variables
A type of star that has turned out to be extremely useful for measuring distances is
the Cepheid variables
Why do Cepheid variables have that strange name?
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:
the length of time they took to vary
The higher the luminosity (intrinsic brightness) a Cepheid variable is,
the longer the period of its variations
How do astronomers know that pulsating variable stars are actually expanding and contracting in diameter?
they can measure a regularly varying Doppler shift in the spectral lines
A light curve for a star measures how its brightness changes with
time
