Question 1

Charles Messier published the first galaxy catalog containing over 2,000 nearby galaxies.

Accepted Answer

A) True 
 B)False  False

Question 2

If the Hubble constant were equal to 50 km/s/Mpc, what would the approximate age of the universe (the Hubble time) be, assuming that the expansion rate has stayed approximately constant over time? Note that 1 Mpc = 3.1 * 1019 km and 1 year = 3.17 * 107 s.

Accepted Answer

The age of the universe would be: 1/H₀ = 1 / (50 km/s/Mpc) = (1 s Mpc)/(50 km) = (1 s * 3.1 * 10¹⁹ km* (1yr / 3.1* 10⁷ s)) / (50 km) F=2 * 10¹⁰ yr =20 billion yr.

Question 3

The existence of the cosmic background radiation tells us that the early universe was:

Accepted Answer

A)  much hotter than it is today 
B)  much colder than it is today 
C)  composed entirely of radiation at early times 
D)  composed entirely of stars at early times 
E)  about the same temperature as today, but was much more dense 
A)  much hotter than it is today 
B)  much colder than it is today 
C)  composed entirely of radiation at early times 
D)  composed entirely of stars at early times 
E)  about the same temperature as today, but was much more dense A

Question 4

Is dark energy responsible for the expansion of the universe?

Accepted Answer

A)  No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to decrease. 
B)  Yes. Dark energy is currently the driving force in the universe's expansion. 
C)  No. Dark energy is only responsible for the observed rapid motions of stars within galaxies. 
D)  No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to increase. 
E)  No. The dark energy has no effect on the expansion. 
A)  No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to decrease. 
B)  Yes. Dark energy is currently the driving force in the universe's expansion. 
C)  No. Dark energy is only responsible for the observed rapid motions of stars within galaxies. 
D)  No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to increase. 
E)  No. The dark energy has no effect on the expansion.

Question 5

What caused early astronomers to believe that our galaxy is only about 6,000 light-years across?

Accepted Answer

A)  Telescopes were not powerful enough to observe stars farther away. 
B)  Interstellar dust blocked visible light from stars farther away. 
C)  Stars farther away could not be resolved as individual objects. 
D)  Astronomers miscalculated the distances to stars, believing that the stars were 50 times closer than they actually were. 
E)  Astronomers assumed all red stars were faint main-sequence stars, and they confused more luminous red giants with them. 
A)  Telescopes were not powerful enough to observe stars farther away. 
B)  Interstellar dust blocked visible light from stars farther away. 
C)  Stars farther away could not be resolved as individual objects. 
D)  Astronomers miscalculated the distances to stars, believing that the stars were 50 times closer than they actually were. 
E)  Astronomers assumed all red stars were faint main-sequence stars, and they confused more luminous red giants with them.

Question 6

How did Edwin Hubble definitively prove that "spiral nebulae" were individual galaxies that were separate from the Milky Way?

Accepted Answer

Hubble identified Cepheid variable stars

Question 7

The Sun is 27 percent helium by mass. Where was the majority of this helium manufactured?

Accepted Answer

A)  in Type II supernovae explosions that happened before the Sun formed 
B)  in low-mass stars that lived and died before the Sun formed 
C)  in nuclear burning that happened in the Sun's core 
D)  in the Big Bang 
E)  by accreting Jupiter-mass planets in the early era of the Solar System 
A)  in Type II supernovae explosions that happened before the Sun formed 
B)  in low-mass stars that lived and died before the Sun formed 
C)  in nuclear burning that happened in the Sun's core 
D)  in the Big Bang 
E)  by accreting Jupiter-mass planets in the early era of the Solar System

Question 8

Type I supernovae have an absolute magnitude of -20. If you discover a Type I supernovae in a distant galaxy that has an apparent magnitude of 22, then how far away is this galaxy?

Accepted Answer

A)  0.3 Mpc 
B)  40 Mpc 
C)  1,200 Mpc 
D)  2,500 Mpc 
E)  3,500 Mpc 
A)  0.3 Mpc 
B)  40 Mpc 
C)  1,200 Mpc 
D)  2,500 Mpc 
E)  3,500 Mpc

Question 9

If the wavelength of the background radiation peaked at 1 $\mu$m at the time of recombination, how old was the universe then compared to its age today?

Accepted Answer

A)  1/10th as old 
B)  1/100th as old 
C)  1/1,000th as old 
D)  1/10,000th as old 
E)  1/100,000 as old 
A)  1/10th as old 
B)  1/100th as old 
C)  1/1,000th as old 
D)  1/10,000th as old 
E)  1/100,000 as old

Question 10

The current temperature of the cosmic background radiation of 2.73 K means that the peak of its spectrum occurs at a wavelength of:

Accepted Answer

A)  0.1$\mu$m 
B)  1$\mu$m 
C)  10 $\mu$m 
D)  100 $\mu$m 
E)  1,000 $\mu$m 
A)  0.1$\mu$m 
B)  1$\mu$m 
C)  10 $\mu$m 
D)  100 $\mu$m 
E)  1,000 $\mu$m

Question 11

Which distance indicator can be used to measure the most distant objects?

Accepted Answer

A)  Cepheids 
B)  parallax 
C)  Type I supernovae 
D)  main-sequence fitting 
E)  RR Lyrae stars 
A)  Cepheids 
B)  parallax 
C)  Type I supernovae 
D)  main-sequence fitting 
E)  RR Lyrae stars

Question 12

The CMB contains photons left over from the epoch in the universe's history when electrons recombined with nuclei.

Accepted Answer

A) True 
 B)False

Question 13

The spectrum of a galaxy is observed to have an H$\alpha$emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H$\alpha$ emission line is 656.3 nm.

Accepted Answer

z=(@#LAT-DLM&_obs -@#LAT-DLM&_rest)/@#LAT-DLM&

Question 14

If suddenly we find that the distances between the Sun and nearby stars are now 10 percent larger than we thought it was before, what measured properties will we not have to adjust?

Accepted Answer

A)  the distances of stars 
B)  the size of our galaxy 
C)  the value of H0 
D)  the fact that the universe is expanding 
E)  the luminosity of Type II supernovae 
A)  the distances of stars 
B)  the size of our galaxy 
C)  the value of H0 
D)  the fact that the universe is expanding 
E)  the luminosity of Type II supernovae

Question 15

After the Big Bang, as the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?

Accepted Answer

A)  Protons and neutrons combined to form nuclei such as deuterium and helium. 
B)  Neutrinos ceased to interact with normal matter. 
C)  Dark matter ceased to interact with normal matter. 
D)  Photons began to travel freely through the universe. 
E)  Lithium and other light elements were formed by the fusion of hydrogen and helium. 
A)  Protons and neutrons combined to form nuclei such as deuterium and helium. 
B)  Neutrinos ceased to interact with normal matter. 
C)  Dark matter ceased to interact with normal matter. 
D)  Photons began to travel freely through the universe. 
E)  Lithium and other light elements were formed by the fusion of hydrogen and helium.

Question 16

In the Great Debate of 1920, Curtis argued that spiral nebulae were individual galaxies, while Shapley argued spiral nebulae must be part of the Milky Way because the Milky Way was very large in size.

Accepted Answer

A) True 
 B)False

Question 17

If the spectrum of a distant galaxy is observed to have a calcium K absorption line that occurs at a wavelength of 500.4 nm, what is this galaxy's distance if the rest wavelength of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc.

Accepted Answer

A)  720 Mpc 
B)  950 Mpc 
C)  1,200 Mpc 
D)  2,500 Mpc 
E)  3,700 Mpc 
A)  720 Mpc 
B)  950 Mpc 
C)  1,200 Mpc 
D)  2,500 Mpc 
E)  3,700 Mpc

Question 18

If a galaxy has a recessional velocity of 50,000 km/s, at what wavelength will you observe the H$\alpha$emission line? Note that the rest wavelength of the H$\alpha$ emission line is 656.3 nm.

Accepted Answer

A)  695.7 nm 
B)  719.4 nm 
C)  742.3 nm 
D)  766.0 nm 
E)  1750 nm 
A)  695.7 nm 
B)  719.4 nm 
C)  742.3 nm 
D)  766.0 nm 
E)  1750 nm

Question 19

Why is it not possible to look all the way back to the Big Bang itself?

Accepted Answer

A)  Photons are not produced until the stars begin to shine at a redshift of z = 20. 
B)  From redshifts of z =0 to 100, photons are gravitationally lensed by the dark matter in the universe. 
C)  At redshifts of z $\gt$ 1,000, most of the photons are blocked by large amounts of cold gas and dust. 
D)  For redshifts of z $\gt$ 1,000, photons are heavily altered because they easily react with individual protons and electrons in the universe. 
E)  Photons from the Big Bang would be so strongly redshifted that we could never detect them. 
A)  Photons are not produced until the stars begin to shine at a redshift of z = 20. 
B)  From redshifts of z =0 to 100, photons are gravitationally lensed by the dark matter in the universe. 
C)  At redshifts of z $\gt$ 1,000, most of the photons are blocked by large amounts of cold gas and dust. 
D)  For redshifts of z $\gt$ 1,000, photons are heavily altered because they easily react with individual protons and electrons in the universe. 
E)  Photons from the Big Bang would be so strongly redshifted that we could never detect them.

Question 20

If we lived in a galaxy one billion light-years from our own, what would we see?

Accepted Answer

A)  a universe 1 billion years younger than ours 
B)  a universe 1 billion years older than ours 
C)  much the same universe we see here 
D)  the universe is expanding at a slower rate than we see from Earth 
E)  the universe is expanding at a faster rate than we see from Earth 
A)  a universe 1 billion years younger than ours 
B)  a universe 1 billion years older than ours 
C)  much the same universe we see here 
D)  the universe is expanding at a slower rate than we see from Earth 
E)  the universe is expanding at a faster rate than we see from Earth

Exam 19: The Expanding Universe

Charles Messier published the first galaxy catalog containing over 2,000 nearby galaxies.

If the Hubble constant were equal to 50 km/s/Mpc, what would the approximate age of the universe (the Hubble time) be, assuming that the expansion rate has stayed approximately constant over time? Note that 1 Mpc = 3.1 * 1019 km and 1 year = 3.17 * 107 s.

The existence of the cosmic background radiation tells us that the early universe was:

Is dark energy responsible for the expansion of the universe?

What caused early astronomers to believe that our galaxy is only about 6,000 light-years across?

How did Edwin Hubble definitively prove that "spiral nebulae" were individual galaxies that were separate from the Milky Way?

The Sun is 27 percent helium by mass. Where was the majority of this helium manufactured?

Type I supernovae have an absolute magnitude of -20. If you discover a Type I supernovae in a distant galaxy that has an apparent magnitude of 22, then how far away is this galaxy?

If the wavelength of the background radiation peaked at 1 μ\muμ m at the time of recombination, how old was the universe then compared to its age today?

The current temperature of the cosmic background radiation of 2.73 K means that the peak of its spectrum occurs at a wavelength of:

Which distance indicator can be used to measure the most distant objects?

The CMB contains photons left over from the epoch in the universe's history when electrons recombined with nuclei.

The spectrum of a galaxy is observed to have an H α\alphaα emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H α\alphaα emission line is 656.3 nm.

If suddenly we find that the distances between the Sun and nearby stars are now 10 percent larger than we thought it was before, what measured properties will we not have to adjust?

After the Big Bang, as the universe cooled and protons and electrons combined so that the universe became neutral, what important consequence happened?

In the Great Debate of 1920, Curtis argued that spiral nebulae were individual galaxies, while Shapley argued spiral nebulae must be part of the Milky Way because the Milky Way was very large in size.

If the spectrum of a distant galaxy is observed to have a calcium K absorption line that occurs at a wavelength of 500.4 nm, what is this galaxy's distance if the rest wavelength of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc.

If a galaxy has a recessional velocity of 50,000 km/s, at what wavelength will you observe the H α\alphaα emission line? Note that the rest wavelength of the H α\alphaα emission line is 656.3 nm.

Why is it not possible to look all the way back to the Big Bang itself?

If we lived in a galaxy one billion light-years from our own, what would we see?

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornmentsmoons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

Relativity and Black Holes

Galaxies

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

If the Hubble constant were equal to 50 km/s/Mpc, what would the approximate age of the universe (the Hubble time) be, assuming that the expansion rate has stayed approximately constant over time? Note that 1 Mpc = 3.1 * 10¹⁹ km and 1 year = 3.17 * 10⁷ s.

If the wavelength of the background radiation peaked at 1 $\mu$ m at the time of recombination, how old was the universe then compared to its age today?

The spectrum of a galaxy is observed to have an H $\alpha$ emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.

If a galaxy has a recessional velocity of 50,000 km/s, at what wavelength will you observe the H $\alpha$ emission line? Note that the rest wavelength of the H $\alpha$ emission line is 656.3 nm.