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3rd Year Winter > P2151 Final > Flashcards

P2151 Final Flashcards

1
Q

Describe the sun

A

star; glowing ball of gas held by gravity and powered by nuclear fusion at the centre

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2
Q

Photosphere

A

region at sun’s surface from which all visible light is emitted

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3
Q

Core

A

interior of sun; nuclear rxns generate E

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4
Q

Radiation Zone

A

Interior of sun; E travels outward in the form of EM radiation

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5
Q

Convection zone

A

interior of sun; Sun’s matter is in constant convective motion

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6
Q

Solar constant

A

the amount of solar E reaching the top of Earth’s atmosphere each second

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7
Q

Luminosity

A

total amount of E radiated from the surface per second.

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8
Q

Where does much of our knowledge of the solar interior come from?

A

Mathematical models

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9
Q

What model best fits the observed properties of the sun?

A

The standard solar model

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10
Q

Helioseismology

A

The study of vibrations of the solar surface caused by P waves in the interior; provides further insight into the Sun’s structure

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11
Q

Granulation

A

shows the effect of solar convection zone; in the photosphere

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12
Q

Supergranulation

A

large transient patterns on the photosphere

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13
Q

Chromosphere

A

Sun’s lower atmosphere. Most absorption lines are produced in upper photosphere and chromosphere

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14
Q

Transition zone

A

Above the chromosphere of sun; T increases from a few thousand to a million K.

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15
Q

Corona

A

Above transition zone of sun; sun’s thin, hot upper atmosphere.

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16
Q

Solar wind

A

The corona begins to flow outward when it escapes the sun’s gravity (about 15 solar radii)

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17
Q

Sunspots

A

Earth-sized regions on solar surface that are a little cooler than the surrounding region. Produce intense magnetism

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18
Q

How often do the number and locations of sun spots vary?

A

11 years

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19
Q

Why does the sunspot cycle happen?

A

The sun’s magnetic field rises and falls. The overall direction reverses from one sunspot cycle to the next. This is a 22-year cycle that results when the direction of the field is taken into account, called the solar cycle

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20
Q

Active regions of Sun

A

Concentrated solar activity; associated with groups of sunspots

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21
Q

Prominences

A

Looplike or sheetlike structures produced when hot gas ejected by activity on the solar surface interacts with the Sun’s magnetic field

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22
Q

Flares

A

intense, violaent surface explosions that blast particles and radiation into interplanetary space

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23
Q

Coronal mass ejections

A

huge blobs of magnetized gas escaping into interplanetary space.

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24
Q

Coronal Holes

A

Low density regions of corona where most of solar wind escapes

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25
Q

Describe the nuclear fusion process

A

hydrogen is converted to helium in the core of the sun

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26
Q

How are nuclei held together?

A

Strong nuclear force

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27
Q

Proton-proton chain

A

4 protons are converted to a helium nucleus, and some mass is lost

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28
Q

Neutrinos

A

Massless particles that are produced in the proton-proton chain; escape from the Sun

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29
Q

How do neutrinos interact?

A

Weak nuclear force

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30
Q

Can we detect neutrinos?

A

A small fraction of them are detectable

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31
Q

Solar neutrino problem

A

Substantially fewer neutrinos are observed than are predicted by theory. The accepted explanation is that neutrino oscillations convert some neutrinos to other particles between the sun and earth.

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32
Q

Trigonometric parallax

A

method of measuring distances, specifically to the nearest stars.

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33
Q

A star with a parallax of 1 arc second is how far from earth?

A

1 parasec, which is about 3.3 light years

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34
Q

Proper motion

A

True motion of a star across the sky. Measures the star’s velocity perpendicular to our line of sight.

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35
Q

How is the star’s radial velocity measured?

A

By the Doppler shift of spectral lines emitted by the star, along the line of sight

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36
Q

Apparent brightness

A

Rate at which E from the star reaches a detector.

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37
Q

Magnitude scale

A

optical astronomers use this to express and compare stellar brightnesses. Greater magnitude, fainter the star.

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38
Q

Apparent magnitude

A

measure of apparent brightness

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39
Q

Absolute magnitude

A

apparent magnitude it would have if placed at a std distance of 10 pc from the viewer. Measure of star’s luminosity.

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40
Q

How do astronomers measure T of stars?

A

By measuring their brightness through 2 or more optical filters and then fitting a blackbody curve

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41
Q

Photometry

A

Measurement of the amt of starlight received through each member of a set of filters

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42
Q

Spectroscopic observations of stars provide an accurate means of determining what?

A

Stellar T and composition

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43
Q

How do astronomers classify stars?

A

According to the absorption lines in their spectra

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44
Q

Standard stellar spectral classes in order of decreasing T:

A

O, B, A, F, G, K, M

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45
Q

Radius-Luminosity T relationship

A

estimates the size of stars.

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46
Q

Dwarfs

A

stars comparable in size or smaller than the sun

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47
Q

Giants

A

Stars up to 100 times larger than the sun

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48
Q

Supergiants

A

stars more than 100 times larger than the sun

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49
Q

Red supergiants

A

large, cool, and luminous

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50
Q

White dwarfs

A

small, hot, and faint

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51
Q

H-R Diagram

A

Plot of stellar luminosity vs. stellar spectral classes or T.

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52
Q

Main sequence

A

about 90% of all stars plotted on a H-R diagram lie here, which stretches from hot, bright blue supergiants to cool, faint red dwarfs (diagnol on the plot)

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53
Q

Are blue or red dwarfs more common?

A

Red

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54
Q

About how many starts are in the white-dwarf region?

A

About 9% of stars

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55
Q

Where do the remaining 1% of stars fall on the H-R diagram?

A

Red-giant region

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56
Q

Spectroscopic parallax

A

method of determining distance by measuring spectral type and luminosity to estimate the distance of a star on the main sequence. Valid for stars up to several thousand parsecs from Earth

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57
Q

Luminosity class

A

allows astronomers to distinguish main-sequence stars from ginats and supergiants of the same spectral type

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58
Q

Many stars are not isolated in space, but orbit other stars in _____

A

Binary-star systems

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59
Q

Visual binary

A

both stars can be seen and their orbits charted

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60
Q

Spectroscopic binary

A

stars cannot be resolved, but their orbital motion can be detected spectroscopically

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61
Q

Eclipsing binary

A

orbit is oriented st one star periodically passes in front of the other, as seen from Earth. This dims the light we receive. This can allow mass determination.

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62
Q

What stars exhaust their fuel rapidly and have much shorter lifetimes than the SUn?

A

High-mass stars

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63
Q

Low-mass stars

A

consume their fuel slowly and may remain on the main sequence for trillions of years

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64
Q

Interstellar medium

A

occupies the space among the stars. Made up of cold (<100K) gas, atomic or molecular hydrogen and helium, and dust grains.

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65
Q

Extinction

A

Diminution of starlight by dust

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66
Q

Reddening of light

A

Dust preferentially absorbs short wavelength radiation, which reddens light passing through interstellar clouds.

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67
Q

What is interstellar dust composed of?

A

Silicates, graphite, iron, ‘dirty ice’

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68
Q

What are interstellar dust particles like?

A

Elongated/rodlike

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69
Q

Polarization of starlight

A

Provides a means of studying interstellar dust particles

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70
Q

Nebula

A

Fuzzy bright or dark patch on the sky

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71
Q

Emission nebulae

A

extended clouds of hot, glowing interstellar gas. They are associated with star formation, when hot O- and B-type stars heat and ionize their surroundings

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72
Q

What does studying the emission lines produced by excited nebular atoms allow astronomers to measure?

A

Properties of nebulae

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73
Q

Dark dust clouds

A

cold, irregularly shaped regions in the interstellar medium whose constituent dust diminishes or obscures the light from background stars

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74
Q

Molecular clouds

A

in interstellar medium; cold, dark, cool and dense enough that much of the gas exists in molecular form. Dust protects molecules and acts as catalyst for their formation.

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75
Q

Molecular cloud complex

A

millions of times more massive than the sun; several molecular clouds found close together

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76
Q

What length of radiation allows cold, dark regions of interstellar space containing atomic hydrogen to be observed in the radio spectrum? How is it produced?

A

21 cm radiation
Produced when the electron in an atom of H reverses its spin

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77
Q

What are molecular clouds observed by?

A

Radio radiation emitted by molecules they contain; radio waves are not absorbed by interstellar medium

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78
Q

What is the most common constituent of molecular clouds?

A

Hydrogen; molecular hydrogen is hard to observe

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79
Q

How do astronomers study the composition of molecular clouds?

A

Other ‘tracer’ molecules that are less common but easier to detect. Many complex molecules have been identified in interstellar clouds

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80
Q

Star formation

A

When an interstellar cloud collapses under its own gravity and breaks up into pieces comparable in mass to our sun.

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81
Q

Evolutionary track

A

evolution of contracting cloud; seen on H-R diagram.

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82
Q

Protostar

A

as a collapsing prestellar fragment heats up and becomes denser, it eventually becomes a protostar. Very warm, luminous object that emits mainly IR. Protostars central T becomes high E to fuse hydrogen, becoming a star.

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83
Q

How long does the star formation process take for a star like the sun? What about more massive/less massive stars?

A

About 50 million years. More massive stars pass through formation stages more rapidly. Less massive stars take much longer to form

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84
Q

Zero-age main sequence

A

region in the H-R diagram where stars lie when the formation process is over

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85
Q

What is the main property in determining a star’s characteristics and lifespan?

A

Mass
More massive stars have shortest lifespans

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86
Q

Brown dwarfs

A

Low-mass fragments that never reach the point of nuclear ignition

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87
Q

What is used in studying early phases of cloud contraction and fragmentation?

A

Radio telescopes

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88
Q

What IR observations allow us to see?

A

Later stages of star formation process.

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89
Q

Protostellar winds

A

powerful; produced by protostars. Encounter less resistance in directions perp to a star’s protostellar disk and expel two jets of matter in direction of protostar’s poles in bipolar flow

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90
Q

Shock waves

A

produced as young hot stars ionize surrounding gas forming emission nebulae. Can compress other interstellar clouds and trigger more star formation

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91
Q

Star Cluster

A

hundreds or thousands of stars

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92
Q

Open clusters

A

few hundred to few thousand stars, found mostly in plane of Milky Way. typically contain bright blue stars; formed recently

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93
Q

Globular clusters

A

found mainly away from Milky Way plane, may contain millions of stars. Include no main-sequence stars larger than sun, indicating they formed long ago.

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94
Q

Core hydrogen-burning phase

A

stably fusing hydrogen into helium at their centers. Stars leave the main sequence when H in core is exhausted.

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95
Q

How far is the sun through its main sequence lifetime?

A

About halfway.

96
Q

Hydrogen shell-burning phase

A

Nonburning He core surrounded by a layer of burning H

97
Q

Subgiant branch and red-giant branch

A

Where a star like the sun moves off the main sequence

98
Q

Electron degeneracy pressure

A

Makes the core unable to react to new E source, and He burning begins violently in a He flash.

99
Q

Horizontal branch

A

after He flash expands the core and reduces star’s luminosity, the star moves here, now having a core of burning He surrounded by a shell of burning H

100
Q

Asymptotic gian branch

A

as He burns in core, it forms an inner core of nonburning carbon. The carbon shrinks and heats the overlying burning layers, and the star becomes a red giant, even more luminous than before

101
Q

Planetary nebula

A

When a stars envelope is ejected into space. Core becomes visible as hot, faint, dense white dwarf, and diffuses into space.

102
Q

Black dwarf

A

white dwarf cools and fades into a cold black dwarf

103
Q

Do high or low mass stars evolve more rapidly?

A

High

104
Q

Which stars never initiate a He flash?

A

High mass

105
Q

Which stars die explosively?

A

High mass

106
Q

Main Sequence-turnoff mass

A

no stars above this mass remain on the main sequence. Stars below this mass have not yet evolved into giants and lie on MS. This can be used to measure a cluster’s age

107
Q

Roche lobe

A

tear-drop shaped which defines the region of space within which matter ‘belongs’ to the star

108
Q

Nova

A

star that suddenly increases greatly in brightness, then slowly fades back to its normal appearance (in a few months)

109
Q

What makes a Nova?

A

the result of a white dwarf in a binary system drawing H-rich material from its companion

110
Q

Accretion disk

A

gas spirals inward and builds up on the white-dwarfs surface, eventually becoming hot and dense enough for H to burn explosively, causing a large increase in dwarf’s luminosity.

111
Q

How big do stars have to be to form heavier elements in their cores?

A

More than 8 solar masses

112
Q

Which heavy element stops the fusion process?

A

Iron

113
Q

When does a star’s core begin to collapse?

A

As it grows in mass, it becomes unable to support itself against gravity

114
Q

Core Collapse Supernova

A

Iron nuclei are broken down into protons and neutrons. Protons combine with electrons to form more neutrons. When the core becomes so dense that neutrons come into physical contact, the collapse stops and core rebounds, sending a violent shock wave out through the rest of the star

115
Q

Type 1 supernovae

A

hydrogen poor and have a light curve similar in shape to that of a nova

116
Q

Type 2 supernovae

A

hydrogen rich and have a plateau in light curve a few months after maximum. This is a core-collapse supernova.

117
Q

Carbon detonation supernova

A

Carbon oxygen white dwarf in a binary system gains mass, collapses, and explodes as its carbon ignites

118
Q

Supernova Remnant

A

shell of exploded debris surrounding the site of the explosion and expanding into space at a speed of thousands of km / s

119
Q

Stellar nucleosynthesis

A

production of new elements by nuclear rxns in the cores of evolved stars

120
Q

Helium capture

A

elements heavier than C tend to form this way. At high core T, photodisintegration breaks apart heavy nuclei, providing He-4 nuclei for synthesis of more massive elements

121
Q

Neutron Capture

A

how elements beyond iron form in the cores of evolved stars.

122
Q

Neutron Star

A

ultracompressed ball of material. Extremely dense, very hot at formation, magnetized, and rapidly rotating. Cool down and lose their magnetism as they age

123
Q

Lighthouse model

A

Neutron stars, because they are magnetized and rotating, send regular bursts of EM E into space. Beams are produced by charged particles confined by strong magnetic fields

124
Q

Pulsar

A

Beams of neutron stars we can see from earth.

125
Q

X-Ray Burster

A

When hydrogen burning starts explosively on star’s surface

126
Q

Rapid rotation of inner part of accretion disk causes neutron star to spin faster as new gas arrives on surface. The rapidly rotating neutron star produces what?

A

A millisecond pulsar

127
Q

Gamma-Ray Bursts

A

Energetic flashes of gamma rays, observed about once a day, distributed uniformly over the sky. Can measure distances, implying extreme luminosity. Theories that these are produced from the violent merging of neutron stars

128
Q

Einstein’s special theory of relativity

A

Behaviour of particles moving at speeds comparable to the speed of light. Agrees with Newton’s theory at low v.

129
Q

Einstein’s general theory of relativity

A

Describes gravity in terms of warping, or bending, of spacetime by the presence of mass. More mass, greater warping.

130
Q

Upper limit on mass of neutron star

A

3 solar masses

131
Q

Black hole

A

region of space from which nothing can escape.

132
Q

Schwarschild radius

A

Radius at which escape speed from a collapsing star equals the speed of light. The sphere of this is called the event horizon

133
Q

What concepts occur around black holes?

A

Gravitational redshift and time dilation.

134
Q

Galaxy

A

huge collection of stellar/interstellar matter isolated in space and bound together by its own gravity

135
Q

Galactic disk

A

appears as a broad band of light across the sky, called the Milky Way.

136
Q

Galactic bulge

A

Disk thickens into this near the centre of the galaxy

137
Q

Galactic halo

A

old stars and star clusters

138
Q

Spiral galaxy

A

Milky Way

139
Q

Variable stars

A

study the halo; luminosity changes with time

140
Q

Pulsating variable stars

A

Vary in brightness in a repetitive and predictable way

141
Q

RR Lyrae Variables / Cepheid variables

A

have same luminosity; can be determined using the period-luminosity relationship. Distance can be determined

142
Q

What does the Galactic halo lack?

A

Gas and dust

143
Q

Are halo stars old?

A

Yes

144
Q

Spiral Arms

A

regions of densest interstellar gas where star formation is taking place.

145
Q

Spiral density waves

A

move through disk, triggering star formation as they pass by

146
Q

Self-propagating star formation

A

When shock waves produced by the formation and evoln of one generation of stars trigger the formation of the next.

147
Q

Galactic Rotation curve

A

plots orbital speed of matter in disk against distance from centre. Can determine mass of galaxy by applying Newton’s laws of motion

148
Q

Dark Halo

A

containing far more mass than can be accounted for in the form of luminous matter

149
Q

Dark Matter

A

In dark halos; unknown composition. Candidates are low mass stars, exotic subatomic particles.

150
Q

Gravitational microlensing

A

Used to study dark matter

151
Q

Hubble Classification Scheme

A

Divides galaxies into several classes, depending on their appearance.

152
Q

Spiral galaxies

A

flattened disks, central bulges, and spiral arms. Old stars in halos

153
Q

Barred-spiral galaxies

A

extended ‘bar’ of material projecting beyond central bulge

154
Q

Elliptical galaxies

A

no disk and contain little or no cool gas/dust, although very hot interstellar gas is observed. Old stars.

155
Q

Irregular galaxies

A

Do not fit into any other category. Rich in gas/dust and are the sites of vigorous star formation.

156
Q

Standard Candles

A

Distance measuring tools. Objects easily identifiable whose luminosities lie within a well-defined range

157
Q

Tully-Fisher relation

A

empirical correlation btwn rotational velocity and luminosity in spiral galaxies

158
Q

Local Group

A

Milky Way, Andromeda, and several other smaller galaxies; gravitationally bound collection

159
Q

Galaxy Clusters

A

consist of many galaxies orbiting one another, bound together by their own gravity

160
Q

What is the nearest galaxy cluster to the Local Group?

A

The Virgo Cluster

161
Q

Hubble’s Law

A

Distant galaxies are observed to be receding from the Milky way, at speeds proportional to their distances from us

162
Q

Hubble’s Constant

A

Proportionality;
70 km/s/Mpc

163
Q

How do Astronomers use Hubble’s law?

A

To determine distances to the most remote objects in the universe

164
Q

Cosmological redshift

A

redshift associated with the Hubble expansion

165
Q

Active galaxies

A

much more luminous; nonstellar spectra, emitting most E outside of visible part of spectrum.

166
Q

Active galactic nucleus

A

Nonstellar activity suggests rapid internal motion

167
Q

Many active galaxies have high-speed, narrow jets of matter shooting out from their central nuclei; the jets transport E from nucleus to where?

A

Radio lobes lying far beyond the visible portion of the galaxy

168
Q

Seyfert galaxy

A

Looks like a normal spiral but has an extremely bright central galactic nucleus. Spectral lines are broad, indicating rapid internal motion

169
Q

Radio galaxies

A

emit large amounts of E in radio part of spectrum

170
Q

Quasars (or quasi-stellar objects)

A

Most luminous objects known; in vis light, they appear starlike, and their spectra are redshifted. All quasars are very distant

171
Q

What is the accepted explanation for the observed properties of all active galaxies?

A

Their E is generated by the accretion of galactic gas onto a supermassive black hole lying in the center

172
Q

What explains the compact extent of the emitting region and high-speed orbit of gas?

A

Small size accretion disk

173
Q

What do typical luminosities of active galaxies require the consumption of?

A

About 1 solar mass of material every few years

174
Q

Synchrotron radiation

A

Charged particles spiraling around magnetic lines produce this, whose spectrum is consistent with radio emission from radio galaxies and jets

175
Q

What do measurements of galaxy and cluster masses reveal?

A

Large amounts of dark matter

176
Q

About what percent of mass in universe is dark matter?

A

90%

177
Q

What do most astronomers think of how large galaxies formed?

A

By the merger of smaller ones and collisions/mergers among galaxies are how galaxies evolve

178
Q

Starburst galaxy

A

may result when a galaxy has a close encounter or collision with a neighbor. This compresses galactic gas, resulting in burst of star formation

179
Q

What do mergers between spirals most likely result in?

A

Elliptical galaxies

180
Q

Evolutionary sequence of galaxies

A

Quasars, active galaxies, normal galaxies

181
Q

Quasar feedback

A

may provide a partial explanation of why masses of black holes are correlated with masses of their parent galaxies.

182
Q

Superclusters

A

galaxy clusters clump together

183
Q

Local Supercluster

A

Virgo cluster, Local group, and several other nearby clusters

184
Q

Voids

A

galaxies/clusters are arranged on surfaces of enormous bubbles of matter surrounding low-density regions

185
Q

What is the origin of voids?

A

closely related to conditions in the very earliest epochs of the universe

186
Q

What can be used as probes of the universe along the observer’s line of sight?

A

Quasar spectra

187
Q

Homogeneous

A

the same everywhere

188
Q

Isotropic

A

the same in all directions

189
Q

Cosmology

A

study of the universe as a whole

190
Q

What is one of the main assumptions of cosmology?

A

The universe is homogeneous and isotopic; known as the principle

191
Q

What does the principle assumption of cosmology imply?

A

The universe cannot have a center or an edge

192
Q

If the universe were homogeneous, isotropic, infinite, and unchanging, what would the night sky look like?

A

Bright, any line of sight would intercept a star

193
Q

Olbers’s paradox

A

The fact that the night sky is dark because we see only a finite part of the universe from Earth

194
Q

Tracing observed motions of galaxies back in time implies what about 14 billion years ago?

A

The universe was a hot, dense primeval fireball that expanded rapidly in the Big Band

195
Q

Did the Big Band happen at a specific location

A

No; space was compressed to a point in that instant; Big Band happened everywhere at once.

196
Q

Two possible outcomes of the current expansion of the universe

A
  1. Expand forever
  2. Eventually recollapse
197
Q

Critical density

A

density of matter needed for gravity alone to overcome the present expansion and cause the universe to collapse

198
Q

What do astronomers think the total mass density of the universe is today compared to the critical density/

A

No more than 30% of the critical density

199
Q

What is the curvature of spacetime determined by?

A

The total density of the universe, including that of matter, radiation, and dark E

200
Q

Closed universe

A

curvature in a high-density universe is sufficiently large that the universe ‘bends back’ on itself and is finite, somewhat like the surface of a sphere

201
Q

Open universe

A

Low density; infinite in extent and has a saddle-shaped geometry

202
Q

Critical universe

A

Density precisely equal to the critical value; spatially flat

203
Q

What do observations of distant supernovae indicate about the expansion of the universe?

A

The expansion of the universe is accelerating, driven by the effects of dark E

204
Q

What does data suggest about the shape of the universe?

A

That it is flat

205
Q

Cosmic microwave background

A

Isotropic blackbody radiation field that fills the entire universe. T around 3K. The existence is direct evidence that the universe expanded from a hot, dense state.

206
Q

What dominates the universe?

A

Dark energy

207
Q

When was the universe matter dominated?

A

When the universe was smaller, a few billion years ago

208
Q

Radiation Dominated

A

The early universe

209
Q

Pair Production

A

During the first few minutes after the Big Band, matter was formed. Particles and forces froze out of the radiation as T fell below threshold. Unequal amount of matter and antimatter

210
Q

Four fundamental forces of nature

A

Gravity
Electromagnetism
Strong nuclear
Weak nuclear

211
Q

Primordial nucleosynthesis

A

Formed most of He in universe today

212
Q

Epoch of Inflation

A

brief period of rapid expansion of the universe, during which the size of the cosmos increased by a factor of 1050 or more

213
Q

Horizon problem

A

according to the standard Big Bang model, there is no good reason for widely separated parts of the universe to be as similar as they are

214
Q

How does inflation solve the horizon problem?

A

Takes a small homogeneous patch of the early universe and expands it enormously.

215
Q

Flatness problem

A

Why the present density is so close to the critical value

216
Q

Cold Dark Matter

A

depends on the T of dark matter at the end of the radiation era; much is cold

217
Q

“Ripples” in the microwave background

A

imprint of early density inhomogeneities on the radiation field

218
Q

Cosmic evolution

A

continuous process that has led to appearance of galaxies, stars, planets, and life on Earth

219
Q

How may living organisms be characterized?

A

By their ability to react to envrmt, grow, reproduce

220
Q

What is strongly favoured by natural selection

A

intelligence

221
Q

What may have led to the formation of amino acids and nucleotide bases?

A

Reactions between simple molecules in the oceans, powered by natural E sources

222
Q

What do amino acids build?

A

Proteins, which control metabolism

223
Q

What do sequences of nucleotide bases build?

A

DNA, genetic blueprint of a living organism

224
Q

What is the best hope for life beyond Earth in the solar system?

A

Mars

225
Q

What other outer planet moons may be possibilities for life of some sort?

A

Europa and Ganymede (Jupiter)
Titan and Enceladus (Saturn)

226
Q

Extremophiles

A

thrive in hostile environments

227
Q

Drake Equation

A

provides a mean of estimating the probability of intelligent life in the galaxy

228
Q

Factors of Drake Eqn

A

galactic star formation rate, likelihood of planets, and number of habitable planets

229
Q

Chemical and biological factors

A

probability that life appears and that is subsequently develops intelligence

230
Q

Cultural and political factors

A

probability that intelligence leads to technology and lifetime of a civilization in technological state

231
Q

What is the likely distance to our nearest intelligent neighbor?

A

Hundreds of parasecs

232
Q

Is space travel a feasible means of searching for intelligent life?

A

No

233
Q

How do we search for extraterrestrial intelligence?

A

Scanning electromagnetic spectrum for signals

234
Q

Water Hole

A

region in the radio range of the electromagnetic spectrum, near the 21-cm line of H and 18-cm line of OH, where natural emissions from the Galaxy happen to be minimized

235
Q

What region is the best part of the spectrum for communication purposes?

A

The water hole

3rd Year Winter (8 decks)

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