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ch.1 astronomy > ch.16 > Flashcards

ch.16 Flashcards

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1
Q

What is the appearance of our galaxy in the night sky?

A

Milky Way

The Milky Way appears as a band of light across the night sky due to the density of stars in the galactic plane.

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2
Q

What is the diameter of the Milky Way galaxy?

A

30 kpc

This measurement is corrected for dust effects and variable star types.

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3
Q

What type of galaxy is the Milky Way?

A

Spiral galaxy

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4
Q

Who was one of the first to measure the Milky Way using visible stars?

A

Herschel

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5
Q

What obstructs the view of the center of the Milky Way?

A

Vast clouds of gas and dust

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6
Q

What are cataclysmic variables?

A

Novae, supernovae, and related phenomena

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7
Q

What are the two types of intrinsic variable stars?

A

RR Lyrae stars and Cepheids

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8
Q

What is the period range for RR Lyrae stars?

A

0.5 to 1 day

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9
Q

What is the period range for Cepheid variables?

A

1 to 100 days

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10
Q

What relationship allows measurement of distances to stars?

A

Period–luminosity relationship

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11
Q

How does the Sun and its neighbors move around the center of the galaxy?

A

220 km/s

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12
Q

What holds all components of the Milky Way together?

A

Gravity

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13
Q

What is differential rotation in the context of the Milky Way?

A

Stars near the center of the galaxy move faster than those near the edge

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14
Q

What is the galactic halo?

A

Spherical region containing very old stars with no gas and dust

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15
Q

Where do the youngest stars and star formation regions exist in the Milky Way?

A

Galactic disk

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16
Q

What surrounds the galactic center?

A

Galactic bulge

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17
Q

What is the nature of stellar orbits in the galactic disk?

A

In a plane and in the same direction

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18
Q

How does the mass of the Milky Way relate to Kepler’s modified third law?

A

Mass is determined using the Sun’s distance to the center and its period of revolution

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19
Q

What is dark matter?

A

Material predicted to account for the discrepancy between observed and calculated mass

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20
Q

What is the estimated age of the Milky Way’s most ancient stars?

A

About 13 billion years old

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21
Q

What is suggested to exist at the center of the Milky Way?

A

An enormous black hole

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22
Q

What is the characteristic color of a reflection nebula?

A

Blue

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23
Q

What is an emission nebula?

Study These Flashcards
A

A region of red ionized gas around hot O or B type stars

24
Q

What is the significance of globular clusters in measuring the Milky Way?

Study These Flashcards
A

They help map the structure of the galaxy

25
What is the Sun's position relative to the disk of the Milky Way?
About two-thirds of the way out in the disk
26
The Milky Way contains approximately how many stars?
100 billion stars
27
The average distance between stars in the neighborhood of the solar system is about ___?
4 light years
28
What fraction of the mass of our Galaxy can we see in all wavelengths?
About 10%
29
What is the typical size of interstellar dust particles?
About a micrometer or less
30
Dust and gas in the Milky Way are concentrated in what area?
A thin layer in the disk
31
What is the primary reason most stars visible to the naked eye are massive, luminous stars?
They are some of the least common by number but brightest stars due to a selection effect. ## Footnote This highlights the bias in our observation of the night sky, where brightness influences visibility.
32
What is one difference between Population I and Population II stars in the Milky Way?
Population I stars have orbits in the disk, while Population II stars have orbits that pass through the disk. ## Footnote This distinction is important for understanding the structure and formation of the Milky Way.
33
In general, how do the ages of Population I stars compare to those of Population II stars?
Population I stars are younger than Population II stars. ## Footnote This age difference reflects the evolutionary processes in the galaxy.
34
In general, how do the masses of Population I and Population II stars differ?
Population I stars are more massive, while Population II stars are typically dwarfs. ## Footnote This relates to the formation environments and stellar evolution paths of these populations.
35
If you plotted open clusters on a star map, how would they be arranged?
They would be concentrated along the Galaxy's disk. ## Footnote Open clusters are often associated with regions of active star formation within the galactic disk.
36
Which statement is not true about open clusters?
Open clusters are gravitationally bound and therefore have a spherical shape. ## Footnote Open clusters are typically not gravitationally bound and can have irregular shapes.
37
What is an irregular dark patch observed in a field of stars likely to be?
A dark nebula. ## Footnote Dark nebulae are regions of dense dust and gas that block light from stars behind them.
38
What defines a bright red nebula as an HII region?
It contains hydrogen atoms which have been ionized by ultraviolet radiation. ## Footnote HII regions are crucial for understanding star formation and the interstellar medium.
39
Compared to a cold molecular cloud at 10 K, how much hotter is an HII region?
About 1,000 times hotter. ## Footnote The temperature difference indicates the energetic processes occurring in HII regions.
40
According to the density-wave theory, why are spiral arms blue?
They contain a lot of young stars formed from clouds compressed by the density wave. ## Footnote This theory explains the formation and appearance of spiral galaxies.
41
Why do astronomers believe there is a black hole at the center of the Milky Way?
It is necessary to explain the galaxy's rotation curve. ## Footnote The gravitational effects observed support the existence of a supermassive black hole.
42
The mass of the black hole at the center of the Milky Way is about _________ solar masses.
5 million ## Footnote This estimation is based on stellar motion studies around the galactic center.
43
What theory offers a likely explanation for the formation of spiral arms?
Density wave theory. ## Footnote This theory describes how spiral arms are created and maintained in spiral galaxies.
44
Does the Milky Way have a sharply defined outer edge?
False ## Footnote The Milky Way gradually transitions into the intergalactic medium rather than having a distinct boundary.
45
Do new surveys suggest brown dwarfs probably outnumber normal stars in our galaxy?
True ## Footnote Brown dwarfs are substellar objects that do not sustain hydrogen fusion.
46
Of the normal matter in the Milky Way, what form does the vast majority take?
Gas and dust. ## Footnote This composition plays a key role in star formation and the dynamics of the galaxy.
47
Has the Milky Way merged with and 'cannibalized' smaller galaxies over its history?
True ## Footnote This process contributes to the growth and evolution of the Milky Way.
48
Can astronomers measure the diameter of the Milky Way Galaxy by plotting the position of globular star clusters?
True ## Footnote Globular clusters serve as indicators of the galactic structure.
49
The solar system is located about _________ kiloparsecs away from the galactic center.
8.5 ## Footnote This distance is essential for understanding our position within the galaxy.
50
The estimated age of the Milky Way galaxy is about _________ billion years.
13 ## Footnote This estimate is based on various dating methods applied to stellar populations.
51
What are the main parts of the Milky Way galaxy?
The disk, the bulge, and the halo. ## Footnote Each component has distinct properties and contributes to the overall structure of the galaxy.
52
What are associations in the context of the Milky Way?
Loose groups of young stars in the spiral arms usually mingled with large clouds of gas and dust. ## Footnote These associations play a role in star formation and the dynamics of the galactic arms.
53
Dust accounts for about _________ percent of the total mass of interstellar matter.
1% ## Footnote Despite its small percentage, dust has significant effects on stellar formation and the interstellar medium.
54
What causes the zone of avoidance?
Dust in the galactic disk that hides stars and galaxies behind it. ## Footnote This phenomenon affects our observations of distant galaxies.
55
Can we detect galaxies in the zone of avoidance using radio telescopes?
True ## Footnote Radio wavelengths can penetrate dust more effectively than optical wavelengths.
56
What is 21 cm emission radiated by?
Hydrogen atoms when electrons drop from the n = 2 energy level to the n = 1 energy level. ## Footnote This emission is crucial for studying the distribution of hydrogen in the universe.
57
Is the intense radio wavelength energy observed in Sagittarius A* emitted by a massive black hole at the center of the Milky Way galaxy?
True ## Footnote Sagittarius A* is identified as the location of the supermassive black hole.

ch.1 astronomy (15 decks)

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