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astronomy 101 > Exam 2 review > Flashcards

Exam 2 review Flashcards

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1
Q

What is Luminosity?

A

The total amount of energy at all wavelengths that a star emits per second. Also could be referred to as apparent brightness.

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2
Q

What is Apparent Brightness?

A

The amount of a stars energy that reaches a given area each second here on Earth. What we see in the sky.

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3
Q

For two stars of the same apparent brightness, the star closer to the Sun will generally have what?

A

A lower luminosity.

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4
Q

Magnitude Scale

A

According to the naked eye, the brightest stars were of magnitude 1, and the dimmest of magnitude 6. Now we know stars that have negative magnitude and large positive magnitudes.

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5
Q

How many times brighter is a magnitude 6 star compared to a magnitude 1 star.

A

100 times brighter

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6
Q

Which sign leads to larger magnitudes, +, or -?

A

Negative apparent magnitudes are brighter.

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7
Q

What do you need in order to calculate a star’s luminosity?

A

Apparent Brightness and Distance to the Star

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8
Q

Color spectrum (ranking) of stars

A

(blue) O B A F G K M (red)
(hot) (cool)

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9
Q

What can analyzing the spectrum of a star tell us?

A

Star size, composition, Radial Velocity, Rotation

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10
Q

What do narrow spectral lines from a star imply?

A

Lower density of gasses in photosphere

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11
Q

What can the doppler effect tell us about the motion of the star?

A

Translational or rotational velocity

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12
Q

Are there more low luminosity stars or more high luminosity stars?

A

Low luminosity, this implies that the stars have a relatively low mass as well.

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13
Q

What is a binary star system? What are the different types of binary star systems?

A

A solar system with two stars. A visual binary is when you can see both stars using a telescope. A spectroscopic binary is one that which looks like one star but is revealed to be two when using spectroscopy.

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14
Q

Mass luminosity relation

A

Luminosity is proportional to the square of the mass

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14
Q

A binary star system has what qualities?

A

composed of two stars
is held together by gravity
is useful to find the mass of he component stars
is not always visually detectable

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15
Q

What are some techniques for measuring the diameter of stars?

A

F = σT^4 (stephan boltzman)
or using a moon passing infront to compare diameter to luminosity decrease

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16
Q

The H-R diagram plots what?

A

plots luminosity versus surface temperature

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17
Q

Are stars bright because of luminosity or proximity?

A

Brightness is more typically due to luminosity then proximity

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18
Q

What are the two most important intrinsic properties for classifying stars?

A

Luminosity and Surface Temperature

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19
Q

What is parallax?

A

apparent motion of objects against distant background from two vantage points.

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20
Q

What is the “distance ladder”

A

It depicts methods to measure distance depending on how far away the object is.

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21
Q

What is an arc minute?

A

1/60 of a degree

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22
Q

relationship to distance in parsecs to angle in arcseconds

A

d(parsec) = 1/θ(arcseconds)

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23
Q

spectroscopic parallax

A

1) measure apparent magnitude
2) assume star lays on the main sequence ( this gives absolute magnitude ( luminosity))
3) apply inverse square law to determine distance

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24
Q

What happens to absorption lines when atmospheric pressure increases

A

absorption lines get broader as pressure increases

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25
Q

What makes a star a Variable star?

A

Stars that are seen to vary in brightness

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26
Q

What do you call a graph that shows how the brightness of a variable star changes with time?

A

a light curve

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27
Q

RR Lyrae stars

A

such stars have essentially the same luminosity curve, with periods from 0.5 to 1 day, all have the same luminosity

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28
Q

Cepheid variable stars

A

Cepheid periods range from about 1 to 100 days, have a luminosity that is strongly correlated with the period of their oscillations

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29
Q

What is interstellar matter?

A

The interstellar medium consists of gas and dust.
Gas is atoms and small molecules, dust is larger clumps of particles

30
Q

How dense is interstellar gas?

A

one atom of gas per cubic centimeter

31
Q

Interstellar gas is composed primarily by…

A

90% hydrogen, 9% helium, and 1% heavier elements

32
Q

What is ionized hydrogen?

A

Gas that is found in Emission nebulae

33
Q

What are Emission nebulae?

A

hot, glowing area associated with the formation of large stars usually part of a larger dust cloud

34
Q

Where is Atomic Hydrogen found?

A

Found in cold regions without stars between dust clouds

35
Q

Where is Molecular hydrogen found?

A

Found in cold dark dust clouds

36
Q

What are HII regions?

A

Emission Nebulae, they are composed of atomic hydrogen gas that is ionized by near-by stars

37
Q

What is the spin flip of an electron?

A

When an electron switches its spin direction, it is a way to emit energy without changing atomic orbital

38
Q

How do we see Interstellar Matter

A

Dust clouds absorb blue light, interstellar matter exists in dark regions

39
Q

What is a nebula?

A

A region of space that is clearly distinguishable through a telescope, but is not sharply defined like a planet or a star

40
Q

Compare nebula size and density

A

Nebula’s are MASSIVE with low density

41
Q

What are cosmic rays?

A

a third class of particle in interstellar space, high-speed atomic nuclei and electrons

42
Q

Where do cosmic rays come from

A

supernova explosions, difficult to tell because of direction change due to magnetic fields

43
Q

Describe stage 1 in star formation

A

Interstellar cloud starts to contract, usually triggered by shock or pressure wave from nearby star. As it contracts, cloud fragments into smaller pieces. Takes a couple million years.

44
Q

Describe stage 2 of star formation

A

individual cloud fragments begin to collapse, once the density is high enough there is no further fragmentation. this contraction produces energy.

45
Q

Describe stage 3 of star formation

A

Spherical gas ball about the size of our solar system,. density is massive, radiation cannot escape. interior is about 10,000 K

46
Q

Describe stage 4 or star formation

A

The core of the cloud is now a protostar, and makes its first appearance on the H-R diagram

47
Q

describe stage 5 of star formation

A

The protostar is still not in equilibrium – outward pressure is becoming a force, but all heating still comes from the gravitational collapse. gets nebular disk, possibly planets.

48
Q

Describe T-Tauri phase of star formation

A

violent surface activity, extremely strong protostellar winds, interaction of winds and disk cause bipolar “jets” emitting energy

49
Q

Describe stage 6 of star formation

A

The core reaches 10 million K, and nuclear fusion begins, PROTOSTAR HAS BECOME A STAR, star continues to contract and increase in temperature, lasts 30,000,000 yr or so

50
Q

Describe stage 7 of star formation

A

The star is in equilibrium, it has reached the main sequence and will remain there as long as it has hydrogen to fuse in its core

51
Q

compare a protostars luminosity to its temperature

A

luminosity increases drastically as temperature rises (stephan boltzman)

52
Q

What is a Brown Dwarf

A

if the mass of the original nebular fragment is too small, nuclear fusion will never begin, failed star, jupiter

53
Q

What is an open cluster

A

loose irregular cluster, found mainly in the plane of the Milky Way, contains few hundred to a thousand stars

54
Q

Globular clusters are…

A

spherical clusters of stars with the absence of massive main-sequence stars, and the heavily populated red giant region, found away from the galactic plane, at least 10 billion years

55
Q

what is an exoplanet

A

planet outside the solarsystem

56
Q

What is a planetary nebula

A

an old star that is shedding its outer layers

57
Q

Describe stage 8 of stellar evolution

A

subgiant status, 100 mill yrs. when the fuel in the core depletes, the core contracts, hydrogen fuses in a shell outside the core
–> energy production increases and star gets brighter

58
Q

Describe stage 9 of stellar evolution

A

red giant status
its luminosity increases enormously due to its large size. He core is tiny, but has 25% of the stellar mass.

59
Q

Describe stage 10 of stellar evolution

A

helium fusion
the helium flash- when helium fuses rapidly, luminosity spikes huge for a short period of time

60
Q

Describe stage 11 of star evolution

A

giant branch, asymptotically
helium in cor fuses to carbon and oxygen
now there are two shells, outward pressure swells the star

61
Q

evolution of star clusters

A

turn off point lowers the older the star cluster gets

62
Q

do all stars undergo the helium flash

A

NO, stars between 4M and 10M do NOT undergo helium flashes

63
Q

Star cores from out to in

A

Hydrogen, Helium, Carbon, Oxygen, Neon, Magnesium, Silicon, Iron

64
Q

Relate a stars mass to its life span

A

higher mass, lower lifespan

65
Q

Describe stage 13 of stellar evolution

A

Fusion ceases, the envelope blows off, leaving a white dwarf to slowly cool

66
Q

Describe stage 14 of stellar evolution

A

White dwarf continues to cool, no more contraction due to electron pressure remains the size of Earth, temperature approaches 0 k, 1 trillion years –> star is dead.

67
Q

What is a neutron star

A

A star that is so dense that electrons are squeezed into the atomic nucleus. They then combine with protons to form neutrons and neutrinos

68
Q

What is a supernova

A

one time violent explosion, once it happens, there is little or nothing left of the progenitor star

69
Q

What is a Type II supernova

A

Fusion of iron core ceases, temperature is 10 bill k
protons and electrons are crushed together, creates shock wave

70
Q

Type Ia supernova
Type Ib supernova
Type Ic supernova

A

Type Ia - posses Si lines in the spectra
Type Ib - Posses He lines in the spectra
Type Ic - anything else

71
Q

What is a black hole

A

post supernova, so dense even electromagnetic radiation cannot escape

72
Q

What is a Novae

A

a star that flares up very suddenly and then returns slowly to its former luminosity

73
Q

What is the Chandrasekhar limit

A

A maximum mass that a white dwarf can have before it collapses and supernovas

astronomy 101 (2 decks)

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