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astronomy > Exam 2: Ch. 3, 5, and 6 > Flashcards

Exam 2: Ch. 3, 5, and 6 Flashcards

1
Q

Tycho Brahe

A
  • most accurate pre-telescope observations
  • his data showed that the positions of the planets deviated from those predicted by Ptolemy’s model
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2
Q

Johannes Kepler

A
  • Brahe’s assistant
  • tasked with analyzing the data to find a satisfactory model of the motion of the planets
  • Kepler did not have full access to Brahe’s data until after Brahe died, and then he was eventually able to unravel the principles governing the motion of the planets
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3
Q

orbit

A
  • path of an object through space
  • can be open or closed
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4
Q

ellipse

A

all the points for which the sum of the distances between two points is always the same: the two points are the foci (one is a focus)

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5
Q

major axis

A

the longest diameter of an ellipse

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6
Q

semimajor axis

A

half of the major exis

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7
Q

eccentricity (e)

A
  • a measurement of its “flatness”
  • relationship of the distance between the foci and the length of the major axis
  • the two extremes are e = 0, which is a circle; and e = 1, which is just a line
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8
Q

foci

A

the two points along the diameter of an ellipse

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9
Q

easy way to find a planet’s average distance to its sun?

A

the length of the semimajor axis

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10
Q

Kepler’s 1st Law

A

Each planet moves around the Sun in an orbit that is an ellipse with the Sun at one focus of the ellipse

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11
Q

do planets change speed throughout their orbit?

A

yes, the planet moves faster when it is closer to the Sun and slower when it is farther from the Sun

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12
Q

Kepler’s 2nd Law

A

The straight line joining a planet and its Sun sweeps out equal areas in space for equal intervals of time

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13
Q

Kepler’s 3rd law

A
  • The square of a planet’s orbital period equals the cube of the semimajor axis of its orbit
  • P^2 = A^3
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14
Q
  • period of Mars is 1.88 years
  • What is Mar’s semi-major axis?
A

(1.88^2)⅓ = 1.52 AU

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15
Q
  • semimajor axis of Saturn is 9.54 AU
  • What is Saturn’s period?
A

(9.54^3)½ = 29.47 years

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16
Q

Newton’s 1st law

A
  • every object will continue to be at rest or move at a constant speed in a straight line unless it is acted on by an outside force
  • “law of inertia”
  • Without an outside force, the motion of an object doesn’t change
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17
Q

momentum =

A

mass x velocity

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18
Q

speed =

A

change in location / time

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19
Q

velocity =

A

directional speed of an object

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20
Q

Newton’s 2nd law

A
  • the change in motion of an object is proportional to and in the direction of a force acting on it
  • F = m x a
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21
Q

acceleration =

A

changes in velocity

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22
Q

Newton’s 3rd law

A
  • for every action, there is an equal and opposite reaction
  • Interactions between objects
  • Object 1 exerts force on object 2, the 2 exerts force on 1 in opposite direction
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23
Q

Conservation of momentum

A

Total momentum of the collection of objects remains the same over time

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24
Q

mass

A

measurement of the amount of matter in an object

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25
Q

volume

A

the amount of space an object takes up

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26
Q

density =

A

mass / volume

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27
Q

Angular momentum

A
  • a measure of rotation of an object around a reference point
  • Product of mass, velocity, and distance from a reference point
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28
Q

Newton’s universal law of gravitation

A

Fg = G x M1 x M2 / R^2
M1M2: masses of two objects
R: distance between their centers
G: gravitational constant, G = 6.67 x 10-11

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29
Q

gravity and distance relationship

A

follows an inverse square law

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30
Q

what determines acceleration due to gravity

A

the central object

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31
Q

weight

A

the gravitational force on an object

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32
Q

perihelion

A

part of orbit closest to Sun

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33
Q

aphelion

A

part of orbit farthest from Sun

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34
Q

perigee

A

the part of a moon/satellite’s orbit that is closest to Earth

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35
Q

apogee

A

a moon/satellite’s farthest point in its orbit from Earth

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36
Q

satellite

A

any object that orbits another object

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37
Q

how far off the ecliptic do all the planets orbit the sun

A

within ~10* of the ecliptic

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38
Q

what are the only planets without moons

A

mercury and venus

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39
Q

where is the asteroid belt

A

between mars and jupiter (2.2 - 2.3 AU)

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40
Q

Low earth orbit

A

Example is ISS
Altitude of 400 km
Orbital speed of 8 km/s
Orbital period of ≈ 90 minutes

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41
Q

what is the escape speed of earth

A

~11 km/s

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42
Q

how fast do waves move?

A

speed of light

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43
Q

wavelength(λ)

A

the distance from crest to crest

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44
Q

frequency(f)

A
  • the number of waves that passes a given point in a given time
  • Measured in Hz
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45
Q

period

A

the time for one wavelength to pass

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46
Q

photon

A

EM light waves acting like a particle

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47
Q

propogation of light

A
  • waves spread out in all directions from the source
  • As the wave gets farther from the source, energy gets spread out more and more
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48
Q

relationship between the intensity of light and distance

A
  • intensity decreases as the distance squared
  • inverse square law
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49
Q

EM spectrum

A

the entire distribution of electromagnetic radiation according to frequency or wavelength

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50
Q

EM spectrum highest to lowest frequency

A

Gamma rays, x-rays, ultraviolet, visible, infrared, microwaves, radio waves

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51
Q

what waves reach earth’s surface

A

Only visible light, radio waves, and some UV and IR reach the surface of the earth

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52
Q

absolute zero

A

defines 0K as the lowest possible temperature

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53
Q

0K =

A

≈ -273*C

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54
Q

blackbody

A

an object that absorbs all radiation hitting it; as it heats up, it radiates until it reaches equilibrium

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55
Q

Wien’s law

A

λ where emission peaks get shorter as the temp rises
λmax =

56
Q

Stefan-Boltzman law

A

power emitted per area
F(energy flux)

57
Q

absolute luminosity

A

the power of a star
L =

58
Q

reflecting

A

light bouncing off a surface at the same angle they arrive

59
Q

refracting

A
  • light bends as it moves through material
  • the higher the frequency, the more the light bends
60
Q

dispersion

A

occurs when light of multiple wavelengths gets refracted, the wavelengths separate

61
Q

spectrometer

A

any device that separates light into different wavelengths

62
Q

stellar spectrum

A
  • what we get when we send a star’s light through a spectrometer
  • In the Sun’s spectrum, we see the rainbow with some colors “missing”, showing up as dark lines
63
Q

what happens when you send white light through a transparent gas

A

you get the same result as a continuous rainbow with dark lines

64
Q

continuous spectrum

A

“full rainbow”, all the colors/wavelengths

65
Q

absorption spectrum

A

continuous spectrum with dark lines(missing wavelengths)

66
Q

emission spectrum

A

a spectrum of the electromagnetic radiation (different wavelengths) emitted by a source

67
Q

how can we determine the makeup of a star?

A

Once we know a specific gas’s spectral fingerprint, we can look for it in the spectrum of a star

68
Q

the makeup of an atom

A
  • All atoms consist of positively charged protons, negatively charged electrons, and uncharged neutrons
  • Protons and neutrons reside in a tightly packed nucleus in the center of an atom
  • Electrons reside around the nucleus
69
Q

atomic number

A

element is determined by the # of protons

70
Q

neutral atoms

A

always have the same number of protons and electrons

71
Q

ion

A

If #s of protons and electron are unequal, the atom has a non-zero charge

72
Q

isotope

A

an atom of an element with different #s of protons and neutrons

73
Q

atomic mass number

A

the # of protons + # of neutrons

74
Q

Bohr model

A

Electrons can only be at certain distances/levels from the nucleus, and at each of these distances/levels, the electron’s energy is constant

75
Q

Orbits(energy levels/states)

A

electron distances from the nucleus

76
Q

what happens when electrons go to a higher/lower state

A

That energy goes in/out as a photon

77
Q

h

A

Plank’s constant

78
Q

Lyman series

A

transitions to/from the ground state (n = 1), emission/absorption of UV light

79
Q

Balmer series

A

transitions to/from the first excited state (n = 2), emission/absorption of visible light

80
Q

Paschen series

A

transitions to/from the second excited state (n = 3), emission/absorption of IR light

81
Q

Bracket series

A

transitions to/from the third excited state (n = 4), emission/absorption of far IR light

82
Q

Pfund series

A

transitions to/from the fourth excited state (n = 5)

83
Q

Humphreys series

A

transitions to/from the fifth excited state (n = 6)

84
Q

what was the first series observed?

A

the Balmer series were the first lines observed (because four of them are in the visible range), and they are often called “H-alpha,” “H-beta,” “H-gamma,” and “H-delta”

85
Q

what is a way that electrons can get up to higher energy levels without a light source?

A

through collisions with other atoms, because temperature is a measure of atomic motion

86
Q

ionization

A
  • if enough energy is absorbed by an electron, it can escape its atom completely
  • atoms can also recapture electrons, giving off one or more photons
87
Q

how can you tell if the source of waves is moving toward an observer?

A

the waves pile up

88
Q

how can you tell if the source of waves is moving away from an observer?

A

the waves become farther apart

89
Q

doppler effect

A

if the source of waves is moving toward an observer, the waves pile up closer together; if the source is moving away, the waves become farther apart

90
Q

blueshift

A

if a light source is moving toward you, the light becomes more blue

91
Q

redshift

A

if a light source is moving away from you, the light becomes more red

92
Q

what does the radial speed of a star need to be to look noticebly redder or bluer?

A

10,000 km/s

93
Q

telescope

A

gathers light

94
Q

instrument

A

separates λ’s

95
Q

aperature

A

the diameter of the opening that allows light into the telescope

96
Q

how much more light do you collect if you double the diameter?

A

4x

97
Q

focus of the lens

A

if all the incoming light rays are parallel, and the curved surfaces of the convex lens are shaped correctly, then all the light rays are refracted to this point

98
Q

focal length

A

distance from the lens to the focus

99
Q

eyepiece

A

to actually see the astronomical object, we then view the image through another lens

100
Q

downsides to refracting telescopes

A
  • the glass has to be perfect all the way through, and both curved surfaces must be perfectly shaped
  • chromatic aberration
  • the lens can only be supported at its edges, which places an upper limit on the size of the lens: if the lens gets too big, gravity will cause it to sag and distort the image
101
Q

chromatic aberration

A

when light is refracted, dispersion occurs; in the context of lenses, this means that different colors are focused at different locations

102
Q

primary mirror

A

design is concave and usually coated with something highly reflective, like silver, aluminum, gold

103
Q

problems solved by reflecting telescopes

A
  • only the reflecting surface needs to be perfect because light doesn’t go through
  • reflection does not result in dispersion, so there is no chromatic aberration
  • a mirror can be supported from below, so it can be much bigger than the lenses in refractors
104
Q

prime focus

A

where the curved primary mirror focuses the light, which is above it in the tube of the telescope

105
Q

secondary mirror

A

a flat mirror that redirects the light away from the prime focus to a viewing location

106
Q

Newtonian focus

A

this design redirects the light sideways to exit the side of the telescope

107
Q

Cassegrain focus

A

this design reflects the light back directly down to exit the telescope through a hole in the middle of the primary mirror

108
Q

active control

A

modern computers correcting/avoiding sagging in real-time

109
Q

Gemini active control

A

measures the sagging multiple times a second and exert forces on the back of the mirror to correct it

110
Q

Keck active control

A

using many mirrors to act as one large mirror

111
Q

what atmospheric obstacles prevent good telescope pictures?

A

weather, water vapor, light pollution, and bad seeing

112
Q

how does weather obstruct telescopes?

A

clouds block light, precipitation could damage the telescope

113
Q

how can water vapor obstruct telescopes?

A

absorbs light (mainly IR) before it reaches the surface

114
Q

light pollution

A

extra light washes out the faint objects

115
Q

bad seeing

A
  • how unsteady the light is due to turbulent air
  • causes twisting and bending of light, resulting in blurry images as well as why stars twinkle
116
Q

resolution

A
  • refers to how sharp images are, the smallest distinguishable features
  • the smallest angle we can resolve
117
Q

how is resolution measured

A
  • in angle on the sky: recall that there are 60 arcminutes in a degree and 60 arcseconds in an arcminute, so one arcsecond is 1/3600 of one degree
  • one arcsecond is the apparent size of a quarter at a distance of 5 km
118
Q

adaptive optics

A
  • a computer system measures the atmospheric distortion and controls a flexible mirror to undo the distortion
  • brings the angular resolution down to 0.1 arcseconds or better in IR light
119
Q

integration time

A

how long the detector is open/observing

120
Q

charge-coupled device (CCD)

A

the detector that sorts visible light

121
Q

Infrared observation challenges

A
  • shortest IR wavelength (~10-6 m) is right around the largest wavelength a CCD can measure
  • much of IR radiation is blocked by the atmosphere
  • Most everyday objects emit IR radiation
  • IR detectors must be heavily shielded
122
Q

spectroscopy

A

investigation and measurement of spectra

123
Q

radio

A

encodes sound into waves in the radio part of the spectrum

124
Q

radio telescope

A
  • consists of a concave reflector made of metal and a detector at the focus of the reflector
  • Detects all radio wavelengths at once
  • Radio telescopes can be located pretty much anywhere and can observe during the day
125
Q

Interferometry

A
  • combine the light collected by more than one telescope
  • The longer the wavelength, the worse the resolution (for a given size dish)
126
Q

interferometer array

A
  • We can get better resolution if we link multiple radio telescopes together
  • Resolution of the interferometer depends on the baseline (separation of telescopes) not the size of the telescopes
127
Q

radar

A

a technique for measuring distance in which you send radiowaves at an object and time how long it rakes for the waves to bounce back

128
Q

what waves don’t reach the earth’s surface?

A

Earth’s atmosphere blocks all gamma rays, x-rays, microwaves, and most UV, so to view those bands, we must put telescopes above the atmosphere

129
Q

the largest airborne IR telescope

A

Stratospheric Observatory for Infrared Astronomy (SOFIA)

130
Q

major space-based IR telescopes

A
  • IR Astronomical Satellite (IRAS)
  • Spitzer Space Telescope
131
Q

Hubble Space Telescope (HST)

A

2.4-m telescope designed for visible-light observations (and a little IR and UV sensitivity, too)

132
Q

Hubble Ultra-Deep Field (HUDF)

A

a 2.4-arcminute square image with a total exposure of nearly 100 hours; it contains over 10,000 galaxies, many of which formed very soon after the Big Bang

133
Q

what wave observations must be done in space?

A

UV, x-ray, and gamma-ray observations must be done in space

134
Q

grazing incidence

A

where x-rays come in and hit the mirror nearly parallel to the mirror so that they actually reflect

135
Q

how can we “observe” gamma rays from the earth’s surface

A
  • by measuring their interaction with the atmosphere
  • Gamma rays excite charged particles in the atmosphere, which then emit their own radiation, which excites other particles and causes them to emit radiation

astronomy (3 decks)

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