Deck 19: Celestial Distances

Question 1

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

Answer 1

the average distance between the Earth and the Sun

Question 2

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

Answer 2

measure the distance directly to any object orbiting the Sun

Question 3

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

Answer 3

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

Question 4

What is the closest star to the Sun?

A) Barnard's Star
B) Sirius
C) Proxima Centauri
D) the Earth
E) we won't know the answer to this until we can travel to the stars

Question 5

If a star is 20 parsecs away, its parallax must be:

A) 20 arcseconds
B) 2 arcseconds
C) ½ arcsecond
D) 1/20^th of an arcsecond
E) this can't be figured out from the information given

Question 6

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

Question 7

The original definition of a meter was

A) the distance from the extended index finger of the Emperor Napoleon to his nose
B) one thousandth of the distance from Paris to London
C) one billionth the distance from the Earth to the Sun
D) one ten-millionth of the distance from the Earth's equator to its pole
E) one thousandth the diameter of the town of Bayonne, New Jersey

Question 8

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

Question 9

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

Question 10

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

Question 11

To establish the scale of the solar system, we need to measure the distance to one object orbiting the Sun. Venus was first used for this purpose, but in the 1930's astronomers organized an international campaign to measure the distance to:

A) Mars
B) the Moon
C) the asteroid Eros
D) Pluto because of its great distance from the Sun
E) Mercury
Section 19.2: Surveying the Stars

Question 12

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

Question 13

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

Question 14

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

Question 15

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

Question 16

What is the baseline that astronomers use to measure the parallax (the distance) of the nearest stars?

A) the diameter of the Earth
B) the distance between observatories in Greenwich, England and Washington, DC
C) the distance between the Earth and the Moon
D) ½ the diameter of the Earth's orbit around the Sun
E) no one can measure parallax for the stars; only for planets in our solar system

Question 17

A light curve for a star measures how its brightness changes with

A) time
B) distance
C) mass
D) radial velocity
E) age

Question 18

If a star is 10 parsecs away, how long ago did the light we see from it tonight begins its journey toward us?

A) 10 years
B) 0.1 years
C) 10,000 years
D) 32.6 years
E) 6100 years

Question 19

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
Section 19.3: Variable Stars: One Key to Cosmic Distances

Question 20

How far away would a star with a parallax of 0.2 arcsec be from us?

A) 2 parsecs
B) 5 parsecs
C) 0.2 parsecs
D) 0.5 parsecs
E) we need more information to answer this question

Question 21

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
Section 19.4: The H-R Diagram and Cosmic Distances

Question 22

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

Question 23

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

Question 24

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

Question 25

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

Question 26

Which of the following stars is a Cepheid variable?

A) Sirius
B) Betelgeuse
C) Rigel
D) Mizar
E) Polaris

Question 27

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

Question 28

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

Question 29

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

Question 30

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

Question 31

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