Question 1

If a globular cluster were 1,000 pc away from us and an RR Lyrae star in it had an absolute magnitude of 0.5, what would its apparent magnitude be?

Accepted Answer

The answer of If a globular cluster were 1,000 pc...

Question 2

How many years does it take the Sun to complete one orbit around the Milky Way? Note that the Sun is traveling at approximately 220 km/s and is 8 kpc from the center of the Milky Way.

Accepted Answer

The time it takes for the sun to orbit around the Milky Way is determined by its distance from the center and its speed. Using the formula Period = 2πr/v, where r is the distance from the center (8 kpc = 8,000 pc = 26,200 light-years) and v is the speed (220 km/s), we can calculate:

Period = 2π(26,200 light-years)/(220 km/s)/1 year per 3.26 light-years
Period = about 230 million years

Therefore, the correct choice is D.

Question 3

Which of these galaxies is most like our own, and what is the name for the type of the galaxy we live in?

Accepted Answer

The galaxy that is most similar to our own is a barred spiral galaxy, which is Galaxy B in the image. Our own galaxy is a barred spiral galaxy known as the Milky Way. Therefore, the best choice is C: Galaxy B is a barred spiral.

Question 4

The Sun is located approximately:

Accepted Answer

The answer of The Sun is located approximately:
...

Question 5

If RR Lyrae stars in a globular cluster had an apparent magnitude of 11.5 and an absolute magnitude of 0.5, what would the globular cluster's distance be?

Accepted Answer

The answer of If RR Lyrae stars in a globular...

Question 6

The Milky Way appears as __________ in the night sky because __________.

Accepted Answer

The Milky Way appears as a faint band of light sprinkled with dark clouds because the Sun lies in the disk of the galaxy. This view is looking through the plane of the galaxy, which is where most of the stars and gas clouds are located. The dark clouds are areas of dust that block the light from background stars.

Question 7

If we found a star cluster at the edge of the disk of the Milky Way at a distance of 10 kpc from the center, which orbited with a velocity of 300 km/s, what would be the total mass enclosed within this radius?

Accepted Answer

Using the equation for the mass enclosed within a radius, 
M = (rv²)/G
where r = 10 kpc (distance from the center of the Milky Way),
v = 300 km/s (orbital velocity), and 
G = 4.3 x 10^-9 kpc^3/(Msun*yr^2) (Gravitational constant)
M = (10 x 3 x 10^5)^2 / (4.3 x 10^-9) 
  = 2 x 10^10 Msun
Therefore, the best choice is (C) 2 x 10^10 Msun.

Question 8

What type of standard candle is used to determine distances to globular clusters?

Accepted Answer

RR Lyrae stars are used as standard candles to determine distances to globular clusters. They are pulsating horizontal branch stars with a period-luminosity relationship that makes them reliable distance indicators.

Question 9

The Milky Way is classified as an __________ galaxy.

Accepted Answer

The Milky Way is classified as an SBbc galaxy, which means it is a barred spiral galaxy with intermediate features between types SBb and SBc.

Question 10

Studying standard candles in globular clusters offered the first conclusive proof that our galaxy was much __________ than originally believed.

Accepted Answer

Studying standard candles in globular clusters showed that our galaxy was much larger than originally believed.

Question 11

The Milky Way Galaxy is a(n) __________ galaxy.

Accepted Answer

The Milky Way Galaxy is a barred spiral galaxy, which means it has a central bar-shaped structure surrounded by spiral arms. This is confirmed by observations and studies of its structure and characteristics.

Question 12

By comparing globular clusters, you find that Cluster A's RR Lyrae stars are 100 times fainter than Cluster B's RR Lyrae stars. You know that Cluster A's stars are 1.5 times more luminous than Cluster B's stars, because Cluster A is more metal-rich and somewhat younger. How do the clusters' distances compare?

Accepted Answer

The answer of By comparing globular clusters, you find that...

Question 13

By comparing globular clusters, you find that Cluster A's RR Lyrae stars are 100 times fainter than Cluster B's RR Lyrae stars. You know that both clusters have approximately the same chemical composition and age, and thus their RR Lyrae stars should have the same luminosities. Which is true about the clusters' distances?

Accepted Answer

The apparent brightness of a star decreases with the square of the distance. If Cluster A's RR Lyrae stars are 100 times fainter, it means Cluster A is 10 times farther away than Cluster B.

Question 14

Imagine you discovered a barred spiral galaxy that was a "Milky Way twin" because the size of the bulge and disk, the arrangement of spiral arms, and other characteristics were just like those in our galaxy. Then you measured its rotation curve and plotted the figure shown below. What would you conclude about this galaxy?

Accepted Answer

The answer of Imagine you discovered a barred spiral galaxy...

Question 15

Why is 21-cm radiation the best way to map the spiral arms in the Milky Way?

Accepted Answer

21-cm radiation is produced by neutral hydrogen atoms, which are abundant in the Milky Way. These photons can pass through the dense clouds of gas and dust in the disk, making it easier to map the spiral arms than with observations at other wavelengths. Additionally, the wavelength of 21-cm radiation is long enough that we can detect clouds of gas without worrying about Doppler shifts due to their orbital velocities.

Question 16

Our galaxy is __________ other galaxies because the dark matter in the Milky Way __________.

Accepted Answer

The Milky Way is similar to other galaxies in that dark matter contains most of the mass in the galaxy.

Question 17

Most of the mass in our galaxy is in the form of:

Accepted Answer

Dark matter is estimated to make up about 85% of the total matter in our galaxy, while stars, gas, and dust only account for the remaining 15%. Globular clusters are collections of stars and are not a significant contributor to the overall mass of the galaxy.

Question 18

What observed property of the Milky Way suggests that it contains a large amount of matter not in the form of stars?

Accepted Answer

The observed property of the Milky Way that suggests the presence of a large amount of matter not in the form of stars is the rotation curve. The rotation curve of the Milky Way shows that the orbital velocities of stars and gas remain relatively constant with increasing distance from the galactic center, instead of decreasing as expected based on the mass of visible matter. This suggests the presence of a large amount of invisible, or dark, matter that is exerting gravitational forces on the stars and gas.

Question 19

Below are two images of the Milky Way at different wavelengths. Which one was taken at infrared wavelengths, and why do you think so?

Accepted Answer

The answer of Below are two images of the Milky...

Question 20

Globular clusters are found in which stellar subgroups of the galaxy?

Accepted Answer

Globular clusters are found in the halo and the inner disk of the galaxy.

Quiz 21: The Milky Waya Normal Spiral Galaxy