QW #19

Today, astronomers can measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter by a. bouncing radar beams off them b. using x-ray telescopes c. using the Hubble Space Telescope to triangulate with d. using Cepheid variable stars that lie behind the planets e. sending graduate students out with very long tape measures

a. bouncing radar beams off them

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

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

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

a. main sequence stars

Kepler's Laws can give us the relative distance of objects in the solar system. To convert these relative distances into actual distances, we need to: a. measure the mass of the Sun b. measure the size of the Earth c. measure the distance directly to any object orbiting the Sun d. measure the length of the year exactly e. measure the exact time it takes for the Earth to spin once on its axis

c. measure the distance directly to any object orbiting the Sun

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

e. 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

Why did it take astronomers until 1838 to measure the parallax of the stars? a. because most stars are too faint to see without a good telescope b. because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope c. because detecting parallax requires measuring a spectrum, which only became possible in the 1830's d. because cepheid variable stars had not been discovered earlier e. because no one before then could conceive of the Earth moving around the Sun

b. because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope

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

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

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

b. measuring the star's parallax

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

b. the Cepheid variables

As astronomers use the term, the parallax of a star is a. one half of the Doppler shift due to its radial velocity b. always equal to 1 AU c. one half the angle that a star shifts when seen from opposite sides of the Earth's orbit d. the time it takes a Cepheid variable star to go through one cycle of its brightness changes e. the time it takes for a star to move one second of arc of proper motion

c. one half the angle that a star shifts when seen from opposite sides of the Earth's orbit

The apparent brightness of stars in general tells us nothing about their distances; we cannot assume that the dimmer stars are farther away. In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be: a. at the same distance b. the same composition c. the same luminosity d. by themselves instead of in binary or double-star systems e. a lot farther away than they presently are

c. the same luminosity

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

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

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

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

If a star is 20 parsecs away, its parallax must be: a. 20 arcseconds b. 2 arcseconds c. ½ arcsecond d. 1/20th of an arcsecond e. this can't be figured out from the information given

d. 1/20th of an arcsecond

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

d. measure the star's Doppler shift from its spectrum

The instrument astronomers are now using to make the most precise measurements of stellar parallax we have ever had is a. the 5-meter (Hale) reflector on Mt. Palomar b. the Very Large Array of radio telescopes c. the Compton Gamma Ray Observatory d. the Gaia satellite in space e. a swimming-pool sized vat of cleaning fluid deep in the shaft of a gold mine

d. the Gaia satellite in space

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

d. 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

d. the length of time they took to vary

An astronomical unit is: a. the distance to the nearest star b. the distance covered by light in one year c. the distance covered by light in one month d. the time it takes for the solar system to turn once on its axis e. the average distance between the Earth and the Sun

e. the average distance between the Earth and the Sun

Which of the following will show the smallest parallax shift? a. the Moon b. the planet Jupiter c. the Sun d. Proxima Centauri, the nearest star e. the star 51 Pegasi, about 50 lightyears away

e. the star 51 Pegasi, about 50 lightyears away