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astronomy > Final: Ch 7, 15, 17, and 18 > Flashcards

Final: Ch 7, 15, 17, and 18 Flashcards

1
Q

how long ago did most of the objects in our solar system form?

A

4.5 BYA

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2
Q

how much of the mass in the solar system is contained in the sun?

A

99.8%

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3
Q

order of the planets from the sun

A

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune

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4
Q

mnemonic for the order of the planets

A

My Very Educated Mother Just Served Us Nachos

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5
Q

what is the most massive planet

A

Jupiter

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6
Q

what direction do all the planets orbit the Sun

A

counter-clockwise from above the Sun’s N pole

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7
Q

trans-Neptunian objects

A

objects farther out in the solar system

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8
Q

dwarf planets

A

the largest trans-Neptunian objects including PLuto and the largest asteroids

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9
Q

qualities of a planet

A

(a) is in orbit around the Sun
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
(c) has cleared the neighborhood around its orbit.

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10
Q

qualities of a dwarf planet

A

(a) is in orbit around the Sun
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
(c) has not cleared the neighborhood around its orbit
(d) is not a satellite.

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11
Q

what are the only planets without a moon

A

Mercury and Venues

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12
Q

name the planet that the moon orbits:
- the moon
- the Galilean moons: Lo, Europa, Ganymede, and Callisto
- Titan
- Triton

A
  • Earth
  • Jupiter
  • Saturn
  • Neptune
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13
Q

asteroids

A

rocky bodies that orbit the Sun, mainly in the asteroid belt between the orbits of Mars and Jupiter

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14
Q

the Trojan (and Greek) asteroids

A

asteroids that share their orbit with Jupiter (because Jupiter’s gravity keeps them there)

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15
Q

comets

A

small, icy bodies made of frozen gases that spend most of their time far from the Sun

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16
Q

cosmic dust

A

countless pieces of “dust” (usually broken rocks) littered across the solar system

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17
Q

meteor

A

when cosmic dust enters the atmosphere, it burns up, causing a brief flash

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18
Q

meteorites

A

larger pieces of meteors that make it to the surface without burning up completely

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19
Q

what are the planets named after

A

Roman deities

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20
Q

what are the planet’s moons named after

A

Greek and Roman mythological figures somehow connected to the planet-deity (except Uranus, whose moons are named after characters in English literature)

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21
Q

what are comets and asteroids named after

A

comets are usually named after their discoverers, while asteroids are named by their discoverers after whatever they like

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22
Q

the giant planets

A
  • Jupiter, Saturn, Uranus, and Neptune
  • Uranus and Neptune are much small than Jupiter and Satun
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23
Q

composition of Jupiter and Saturn

A
  • mostly H and He
  • Very small solid core of rock, metal, and ice
  • Much of the H and He is compressed until it becomes liquid, so the next layer is “spherical ocean”
  • Gaseous atmosphere that we see
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24
Q

terrestrial planets

A
  • Mercury, Venus, Earth, Mars
  • All 4 are much smaller than the outer planets
  • Composed of rock and metal
  • Most of the heavier metals are in the cores
  • The layered structure of terrestrial planets indicates that they were molten at some point
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25
Q

what is the most common rock in the terrestrial planets

A

Silicates (compounds of silicon)

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26
Q

what is the most common metal in the terrestrial planets

A

Iron

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27
Q

differentiation

A

The process in which materials are separated into layers according to density by gravity

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28
Q

what is the composition of moons?

A
  • similar to that of their planets
  • most are differentiated
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29
Q

are asteroids and comets differentiated?

A

no

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30
Q

Greenhouse effect

A
  • Visible light easily passes through an atmosphere then planets absorb the light, heat up, and emit IR; the atmosphere blocks IR, keeping it in
  • water and COs are molecules that absorb/block IR
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31
Q

what happened to Venus’s atmosphere

A

had a “runaway” greenhouse effect

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32
Q

why are there no impact craters on Earth?

A
  • internal forces that can change surfaces as well:
  • Plate tectonics and volcanism
  • Collectively, this is called geological activity
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33
Q

geological activity

A
  • Driven by heat in the interior of a planet: heat escaping (or at least trying to) is what causes tectonic plate movement, volcanic eruptions, etc
  • most terrestrial bodies were molten at one time, and a molten interior is what leads to geological activity
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34
Q

what is the correlation between impact craters and age of a planet?

A
  • The more craters there are, the older the surface is
  • The bigger the crater is, the more likely it is to be older
  • If there is no geological activity, the age of the surface is the age of the planet
  • If there is geological activity, the age of the planet will be older than the surface
  • We can count craters on different parts of a planet’s surface to get the relative ages of those parts
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35
Q

radioactive decay

A

Some atoms are not stable, so over time, they decay into other, more stable atoms, giving off particles or gamma rays

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36
Q

half life

A

the time it takes for half the atoms in a sample to decay

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37
Q

how does the hald life dating process work

A
  • Once we determine the half-life of a substance and its decay products (what it decays into) we can find the age of any sample
  • From the original amount of the original substance to the decay product, we can find how many half-lives have passed, and then age
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38
Q

what is the relationship between a sun’s rotation and its planets’ orbits?

A

All planets orbit the sun in the same direction, which is also the direction of the sun’s rotation

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39
Q

solar nebula

A

rotating cloud of dust that the sun and all the planets formed from

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40
Q

building of a solar system

A
  • solar nebula became a rotating disk, which then became the sun, planets, etc.
  • Terrestrial planets and asteroids are all in the inner solar system (hot enough for gases and liquids to evaporate, but rocks and metals could survive)
  • Giant planets, their moons, and comets are further out and have much more gas (cooler)
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41
Q

building a giant planet

A

clumps of gas move together randomly, their increased gravity pulls in more clumps, until you have a giant planet

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42
Q

building terrestrial planets

A
  • rocks and metals form small clumps called planetesimals
  • planetesimals combine to form planets via collisions that make them stick together
  • eventually, an incredible multitude of planetesimals have combined, heated by their collisions and radioactive decay
  • as the collection of planetesimals settles, differentiation occurs, and eventually the surface cools and solidifies into the crust of a terrestrial planet
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43
Q

planetesimals

A

rocks and metals from small clumps

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44
Q

what can explain the abnormal rotations of Venus, Uranus, and Pluto

A

the “abnormal” rotations of Venus (slow retrograde rotation), Uranus (on it side), and Pluto (on its side) can also be explained by these collisions: in the later stages of formation, a large (but not planet-sized) chunk of planetesimals might have hit the planet, reorienting its rotation axis

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45
Q

what is the size relationship between the sun and earth

A

it has a diameter equal to 109 times the diameter of the Earth, and thus a volume of about 1.3 million Earths

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46
Q

chemical makeup of the sun

A

73% hydrogen, 25% helium, 2% everything else

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47
Q

plasma

A
  • hot ionized gas
  • positively charged nuclei and negatively charged electrons
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48
Q

sun’s core

A
  • incredibly dense due to gravity
  • it takes up about 20% of the Sun’s interior, has a temperature of about 15 million K, and it is where all the Sun’s energy is generated
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49
Q

source of the sun’s energy

A
  • nuclear fusion
  • mainly occurs in the form of the proton-proton chain, a series of reactions involving collisions of hydrogen nuclei
  • four hydrogen nuclei become one helium nucleus, giving off gamma rays and neutrinos
  • the reason so much energy is released is that one helium nucleus has ever so slightly less mass than four hydrogen nuclei; about 0.71% less mass
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50
Q

layers of the sun

A
  • core
  • radiative zone
  • convection zone
  • solar photosphere
  • chromosphere
  • transition region
  • corona
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51
Q

radiative zone

A
  • extends out to about 70% of the Sun’s radius
  • the light from the core radiates outward but makes very slow progress: before moving too far, it gets deflected by a particle, so it follows a “random walk” outward and loses energy in the process
52
Q

convection zone

A
  • extends to the surface of the Sun; it is about 200,000 km thick
  • energy is transported outward by convection, not radiation
53
Q

explain convection in the sun

A

the bottom of this zone is heated by the radiation, causing the plasma to rise upward toward the surface, where it loses energy to space, causing it to cool and sink back down, forming large loops of moving material, called convection cells

54
Q

solar photosphere

A
  • photons working their way out from the inner layers can finally move unimpeded by dense material
  • ~ 400 km thick and average temperature of 5800 K
  • much less density and pressure than Earth’s atmosphere
  • not uniform in appearance: it is composed of granules, bright regions with diameters of about 700-1000 km, divided from each other by narrow darker regions
55
Q

“radius of the sun”

A

because the photosphere is where the Sun becomes opaque, the photosphere is the visible “surface” of the Sun, so when we talk about the “radius of the Sun,” we are talking about the distance between the center and the photosphere

56
Q

granules

A
  • bright regions with diameters of about 700-1000 km, divided from each other by narrow dark regions
  • only last 5 to 10 minutes (photosphere changes rapidly)
  • the tops of the convection cells below, and the dark areas, about 100 K cooler, are where the material sinks back down
57
Q

chromosphere

A
  • above the photosphere
  • temperature around 10,000 K, hotter than the photosphere
  • its spectrum of bright emission lines indicates it is composed of hot gases; because hydrogen dominates, the strongest emission line is H-α, which is red
  • the spectrum of the chromosphere that led to the discovery of helium
58
Q

transition region

A
  • above the chromosphere
  • the temperature rises from 10,000 K to over one million K
    further, this region is less than 100 km thick
  • we still do not know exactly how this temperature increase occurs
59
Q

corona

A
  • the outermost layer of the Sun’s atmosphere
  • this layer is what is most visible during a total solar eclipse because it extends for millions of kilometers above the photosphere
  • the photosphere is just so much brighter, which is why we do not see the corona all the time
  • can also be viewed using a coronagraph on a space telescope: a circular disk is placed in front of the telescope to exactly cover the photosphere, just like the Moon does during a total solar eclipse
  • the corona has a very low density (10^9 atoms per cm^3 at the bottom vs 10^16 atoms per cm^3 in photosphere and 10^19 molecules per cm^3 in Earth’s atmosphere at sea level)
  • it also thins out as you get farther from the center of the Sun, but technically extends out extremely far, becoming the solar wind
60
Q

solar wind

A
  • a stream of charged particles given off by the sun’s atmosphere
  • move outward at about 400 km/s
  • the particles come from the corona: the particles are moving so quickly (due to the intense temperatures) that the gravity of the Sun cannot keep them bound
61
Q

coronal holes

A
  • the dimmer regions of the complex corona
  • Most of the solar wind escapes from coronal holes
62
Q

sunspots

A
  • Dark regions on the surface of the sun, caused by magnetic interactions
  • They appear dark because they are at a lower temp (3800K) than surroundings
  • Larger sunspots have darker umbras surrounded by a lighter penumbra
  • They usually appear in clusters of 2-20, or up to ~100
63
Q

sunspots

A
  • Dark regions on the surface of the sun, caused by magnetic interactions
  • They appear dark because they are at a lower temp (3800K) than the surroundings
  • Larger sunspots have darker umbras surrounded by a lighter penumbra
  • They usually appear in clusters of 2-20, or up to ~100
64
Q

what kind of rotation does the sun undergo?

A
  • differential rotation
  • Rotates at different rates at different latitudes
65
Q

sunspot cycle

A
  • During sunspot maximum, there can be 100+ sunspots visible at once
  • During sunspot minimum, there might not be any
  • full cycle lasts around 22 years
  • polarities of leading spots flip each cycle
  • That means that the overall magnetic field of the sun flips each cycle
66
Q

Zeeman effect

A

When a magnetic field is present, each energy level of an atom gets split into multiple, very close levels, so spectral lines get split, too

67
Q

sunspot effect on the magnetic field

A

the magnetic field is stronger at locations of sunsoits

68
Q

why do sunspots appear in pairs?

A
  • because magnetic N and S poles occur in pairs, each spot “represents” a pole
  • Large groups of sunspots are complex, but the 2 principal spots play these roles
69
Q

magnetogram

A

an image showing the magnetic field strength at each location

70
Q

what creates the sun’s magnetic field?

A
  • The churning of solar material in the convective zone
  • convection and differential rotation cause the field to get twisted up
71
Q

where do sunspots form?

A

strong fields can form loops in field lines

72
Q

why are sunspots cooler

A

because the strong field suppresses convection

73
Q

plages

A
  • bright “clouds” around sunspots in the chromosphere
  • higher density and temp than surrounding material
74
Q

prominences

A
  • filaments of hot plasma near sunspots
  • extend from the surface and into the corona
75
Q

solar flare

A
  • an eruption on the surface that releases a lot of material and energy over a short time
  • near the maximum of the cycle, there can be several each day
  • When fields of opposite polarity interact on the surface, they destroy each other, releasing the energy stored in the field
  • Can trigger coronal mass ejections
76
Q

coronal mass ejections (CMEs)

A

which material in the corona is flung away from the sun

77
Q

active regions

A

areas near sunspots, caused by magnetic fields where solar flares and CMEs occur

78
Q

space weather

A

solar wind, solar flares, and CMEs

79
Q

what does solar wind do to Earth?

A

distorts earth’s magnetic field, which can cause minor EM disturbances on earth

80
Q

what do solar flares do to Earth?

A

X-rays and charged particles can damage satellites

81
Q

what do CMEs do to Earth?

A
  • Bubble of matter and energy from CME heats the ionosphere, which expands putting more atmospheric drag on more satellites
  • Even if satellites are physically effected, their signals can get distorted by CMEs
  • A CME rapidly changes shape of Earth’s magnetic field, and changing magnetic fields produce electric fields and electric currents
  • This can cause power surges, which can blow transformers, leading to blackouts
82
Q

luminosity

A
  • Total energy output across the entire EM spectrum
  • Most fundamental measurement of a star’s brightness
  • We often represent luminosity in terms of Sun’s
    Lo = Lsun = 3.8 x 10^26 W
  • Unfortunately, L cannot be measured directly
83
Q

apparent brightness

A
  • Only a small fraction of a star’s energy reaches the earth
    “the energy we receive from a star that hits x given area each second”
  • Different brightnesses can be due to different factors:
    • Different intrinsic luminosities
    • Different distance
84
Q

photometry

A

the process of finding brightness

85
Q

Hipparchus’s magnitude scale

A
  • divided all visible stars into 6 categories or magnitudes
  • Brightest: 1
  • Dimmiest: 6
  • The standard system made this exact: a difference of 5 magnitudes corresponds to a factor of 100 in brightness
  • magnitudes go backward: higher magnitude means lower brightness
  • Stars can have fractional magnitudes or negative magnitudes
86
Q

brightness and mass equation

A

b2/b1 = 100^(m1-m2)/5
or
m1-m2 = 2.5 x log↓10(b2/b1)

87
Q

star temp range

A

~2,000K to 40,000+K

88
Q

Our Sun’s temp

A

(5800K) peaks in greenish-yellow

89
Q

A popular set of filters for color indices

A

U: (UV) 360nm
B: (blue) 420nm
V: (visible/yellow) 540nm

90
Q

color indices

A

differences between colors

91
Q

what are color indices at when a star is 10,000K

A

0

92
Q

what causes different spectral lines being more or less prominent

A

different temps

93
Q

what is the ideal star temp

A

~10,000K

94
Q

spectral classes (spectral types) from highest temp to lowest:

A
  • O, B, A, F, G, K, M, | L, T, Y
  • Each class has 10 subclasses labeled 0-9 (0 being the hottest)
95
Q

what spectral class is our sun in ?

A

G2

96
Q

metals

A

all elements besides H and He

97
Q

brown dwarfs

A
  • Objects with temps below those of M9 are not “true” stars
  • They have < 7.5% mass of the Sun, so they never get hot enough to have fusion occur like in the Sun
  • about the same size as Jupiter, but range from ~13MJ to 80MJ
  • Difference is brown dwarfs support deuterium fusions; planets do not
98
Q

giants and supergiants

A
  • very large stars
99
Q

what is the relationship between star size and spectral lines?

A
  • Larger star has narrower spectral lines than a smaller one
100
Q

why does a larger star have narrower lines

A
  • Larger star has larger photosphere, so the material has a lower density and pressure than that of a smaller star
  • Lower density and pressure→ fewer collisions→ narrower lines
101
Q

what is the relationship between star size and ionized material

A
  • Larger star has more spectral lines from ionized material than small star at the same temp:
  • # of atoms that get ionized depends on temp, so it is the same in both stars
  • Atoms stay ionized longer in large star because low density makes it less likely that ion will interact with electron
  • We will get stronger spectral lines from ions because the ions are around longer
102
Q

metallioity

A

the fraction of a star that is composed of metals

103
Q

proper motion

A
  • motion of star across the sky relative to background stars
  • These motions are incredibly small
  • Measured in arc seconds per year
  • If we also know the distance to the star, we can get its speed across the sky (transverse velocity)
104
Q

how can we find radial velocity

A

doppler shift in spectrum

105
Q

how can we find a star’s space velocity

A

radial velocity and transverse velocity

106
Q

rotation and Doppler shifts

A
  • As long as an object’s rotation axis doesn’t point directly toward us, one side will move toward us and the other will move away due to rotation
  • In star’s spectrum, rotation appears as line broadening: the faster the rotation, the broader the lines become
  • It is due to different points on a star having different Doppler shifts
107
Q

lightyear =

A
  • 1 ly = 9.46 x 1012 km = 63,241 AU
  • It is a unit of distance not time
108
Q

why do most of the stars visible to the naked eye appear bright?

A

because they are many times brighter than our sun, but far awat

109
Q

binary stars

A
  • A system with two stars orbiti ng their common center of mass
  • incredibly common
110
Q

double star

A
  • 2 stars that appear close in the sky
  • It might be binary, but more likely, it is just a coincidence based on POV
111
Q

visible binary

A

one that can be seen with a telescope

112
Q

spectroscopic binary

A
  • binary that is revealed by its spectrum:
  • We get spectral lines of both stars together
  • When one star is moving away (redshifted) and the other is moving toward us (blueshifted), we see both sets of lines
  • When they are moving across our view, the lines lie on top of each other
  • Consistent pattern of 2 sets of lines becoming 1 set and back indicates a binary star
113
Q

how does Kepler’s 3rd law relate to binary stars

A
  • A^3 = (M1+M2) x P^2
  • Spectrum gives us radial velocities, which gives us period of orbit
  • With velocities and periods, we can find the distance the stars travel in one orbit (circumference of orbit) and thus semimajor axis
  • This allows us to get total mass of both stars together
  • Also with additional knowledge of the nature of the system, we can find the ratio of masses, and thus the individual masses
114
Q

Mass and luminosity

A
  • With some exceptions, luminosity scales with mass
  • Mass-luminosity relation: states that L ~ M^3.9
  • L/Lo = (M/Mo)4
115
Q

stars blocked by the moon and size

A
  • When the moon is blocking a star, the star dims, once the moon is fully blocking it, it disappears
  • From the time that this process takes and known speed of the moon across the sky, we can find the angular diameter of the star
  • If we know the distance to the star, we can find physical diameter
116
Q

Eclipsing binary stars

A
  • Relative depths in the dips incurve tell us about relative brightness
  • Bigger dip, bigger eclipsed star
  • When smaller stars start to pass behind (1st contact), curve starts to dip
  • When “ “ disappears (2nd contact), we’ve reached the bottom
  • When “ “ begins reappearing (3rd contact), curve starts to rise
  • When “ “ has completely emerged (last contact), curve is back to a normal level
  • Between 1st and 2nd contact, small star moves distance equal to its own diameter
  • Between 1st and 3rd contact small star moves distance of big star’s diameter
  • With those times and relative speeds of stars (from spectrum), we can find these distance
117
Q

energy flux and luminosity relationship

A
  • If 2 stars have the same temp (T1=T2), then F1 = F2
  • Thus, any differences in L are due to differences in size
118
Q

Luminosity and size relationship

A

-If we know luminosities (brightnesses and distances), then we can find sizes
- L1/L2 = R1^2/R2^2

119
Q

The Hertzsprung-Russell diagram (D-R diagram)

A
  • plots L vs T
  • By convention, T increases to the left so that spectral types are in order
  • Main Sequence: About 90% of all stars lie along a band from the upper left (High L, High T) to the lower right (low L, low T)
  • Upper right is home to red/supergiants
  • White dwarfs are located in the lower left of
120
Q

proportions of Hertzsprung-Russell diagram

A

MS: ~90%
WD: ~10%
Giants: ~1%

121
Q

proportion of a star’s life that it spends at different stages

A

each star spends ~90% of its life on MS, ~10% of its life on WD, and ~1% on giants

122
Q

what does main sequence correspond to

A

stars that are actively fusing H to He

123
Q

mass relationship on the Hertzsprung-Russell diagram

A

High M→ high L, high T
Low M→ low L, low T

124
Q

what happens when a star runs out of H in its core

A
  • it contracts and expands as it fuses heavier and heavier elements, eventually becoming a red giant or red supergiant
  • After all possible fusion reactions run out, gravity takes over completely, compressing a star into a white dwarf
125
Q

white dwarfs

A
  • High temps because they are so compressed
  • not very luminous
  • Masses comparable to Sun’s, but are around the size of earth, so they are extremely dense
  • This is the last stage/end result for many MS stars

astronomy (3 decks)

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