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
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
3
Q
orbit
A
- path of an object through space
- can be open or closed
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)
5
Q
major axis
A
the longest diameter of an ellipse
6
Q
semimajor axis
A
half of the major exis
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
8
Q
foci
A
the two points along the diameter of an ellipse
9
Q
easy way to find a planet’s average distance to its sun?
A
the length of the semimajor axis
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
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
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
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
14
Q
- period of Mars is 1.88 years
- What is Mar’s semi-major axis?
A
(1.88^2)⅓ = 1.52 AU
15
Q
- semimajor axis of Saturn is 9.54 AU
- What is Saturn’s period?
A
(9.54^3)½ = 29.47 years
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
17
Q
momentum =
A
mass x velocity
18
Q
speed =
A
change in location / time
19
Q
velocity =
A
directional speed of an object
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
21
Q
acceleration =
A
changes in velocity
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
23
Q
Conservation of momentum
A
Total momentum of the collection of objects remains the same over time
24
Q
mass
A
measurement of the amount of matter in an object
25
volume
the amount of space an object takes up
26
density =
mass / volume
27
Angular momentum
- a measure of rotation of an object around a reference point
- Product of mass, velocity, and distance from a reference point
28
Newton’s universal law of gravitation
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
29
gravity and distance relationship
follows an inverse square law
30
what determines acceleration due to gravity
the central object
31
weight
the gravitational force on an object
32
perihelion
part of orbit closest to Sun
33
aphelion
part of orbit farthest from Sun
34
perigee
the part of a moon/satellite's orbit that is closest to Earth
35
apogee
a moon/satellite's farthest point in its orbit from Earth
36
satellite
any object that orbits another object
37
how far off the ecliptic do all the planets orbit the sun
within ~10* of the ecliptic
38
what are the only planets without moons
mercury and venus
39
where is the asteroid belt
between mars and jupiter (2.2 - 2.3 AU)
40
Low earth orbit
Example is ISS
Altitude of 400 km
Orbital speed of 8 km/s
Orbital period of ≈ 90 minutes
41
what is the escape speed of earth
~11 km/s
42
how fast do waves move?
speed of light
43
wavelength(λ)
the distance from crest to crest
44
frequency(f)
- the number of waves that passes a given point in a given time
- Measured in Hz
45
period
the time for one wavelength to pass
46
photon
EM light waves acting like a particle
47
propogation of light
- waves spread out in all directions from the source
- As the wave gets farther from the source, energy gets spread out more and more
48
relationship between the intensity of light and distance
- intensity decreases as the distance squared
- inverse square law
49
EM spectrum
the entire distribution of electromagnetic radiation according to frequency or wavelength
50
EM spectrum highest to lowest frequency
Gamma rays, x-rays, ultraviolet, visible, infrared, microwaves, radio waves
51
what waves reach earth's surface
Only visible light, radio waves, and some UV and IR reach the surface of the earth
52
absolute zero
defines 0K as the lowest possible temperature
53
0K =
≈ -273*C
54
blackbody
an object that absorbs all radiation hitting it; as it heats up, it radiates until it reaches equilibrium
55
Wien's law
λ where emission peaks get shorter as the temp rises
λmax =
56
Stefan-Boltzman law
power emitted per area
F(energy flux)
57
absolute luminosity
the power of a star
L =
58
reflecting
light bouncing off a surface at the same angle they arrive
59
refracting
- light bends as it moves through material
- the higher the frequency, the more the light bends
60
dispersion
occurs when light of multiple wavelengths gets refracted, the wavelengths separate
61
spectrometer
any device that separates light into different wavelengths
62
stellar spectrum
- 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
what happens when you send white light through a transparent gas
you get the same result as a continuous rainbow with dark lines
64
continuous spectrum
“full rainbow”, all the colors/wavelengths
65
absorption spectrum
continuous spectrum with dark lines(missing wavelengths)
66
emission spectrum
a spectrum of the electromagnetic radiation (different wavelengths) emitted by a source
67
how can we determine the makeup of a star?
Once we know a specific gas’s spectral fingerprint, we can look for it in the spectrum of a star
68
the makeup of an atom
- 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
atomic number
element is determined by the # of protons
70
neutral atoms
always have the same number of protons and electrons
71
ion
If #s of protons and electron are unequal, the atom has a non-zero charge
72
isotope
an atom of an element with different #s of protons and neutrons
73
atomic mass number
the # of protons + # of neutrons
74
Bohr model
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
Orbits(energy levels/states)
electron distances from the nucleus
76
what happens when electrons go to a higher/lower state
That energy goes in/out as a photon
77
h
Plank's constant
78
Lyman series
transitions to/from the ground state (n = 1), emission/absorption of UV light
79
Balmer series
transitions to/from the first excited state (n = 2), emission/absorption of visible light
80
Paschen series
transitions to/from the second excited state (n = 3), emission/absorption of IR light
81
Bracket series
transitions to/from the third excited state (n = 4), emission/absorption of far IR light
82
Pfund series
transitions to/from the fourth excited state (n = 5)
83
Humphreys series
transitions to/from the fifth excited state (n = 6)
84
what was the first series observed?
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
what is a way that electrons can get up to higher energy levels without a light source?
through collisions with other atoms, because temperature is a measure of atomic motion
86
ionization
- 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
how can you tell if the source of waves is moving toward an observer?
the waves pile up
88
how can you tell if the source of waves is moving away from an observer?
the waves become farther apart
89
doppler effect
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
blueshift
if a light source is moving toward you, the light becomes more blue
91
redshift
if a light source is moving away from you, the light becomes more red
92
what does the radial speed of a star need to be to look noticebly redder or bluer?
10,000 km/s
93
telescope
gathers light
94
instrument
separates λ’s
95
aperature
the diameter of the opening that allows light into the telescope
96
how much more light do you collect if you double the diameter?
4x
97
focus of the lens
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
focal length
distance from the lens to the focus
99
eyepiece
to actually see the astronomical object, we then view the image through another lens
100
downsides to refracting telescopes
- 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
chromatic aberration
when light is refracted, dispersion occurs; in the context of lenses, this means that different colors are focused at different locations
102
primary mirror
design is concave and usually coated with something highly reflective, like silver, aluminum, gold
103
problems solved by reflecting telescopes
- 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
prime focus
where the curved primary mirror focuses the light, which is above it in the tube of the telescope
105
secondary mirror
a flat mirror that redirects the light away from the prime focus to a viewing location
106
Newtonian focus
this design redirects the light sideways to exit the side of the telescope
107
Cassegrain focus
this design reflects the light back directly down to exit the telescope through a hole in the middle of the primary mirror
108
active control
modern computers correcting/avoiding sagging in real-time
109
Gemini active control
measures the sagging multiple times a second and exert forces on the back of the mirror to correct it
110
Keck active control
using many mirrors to act as one large mirror
111
what atmospheric obstacles prevent good telescope pictures?
weather, water vapor, light pollution, and bad seeing
112
how does weather obstruct telescopes?
clouds block light, precipitation could damage the telescope
113
how can water vapor obstruct telescopes?
absorbs light (mainly IR) before it reaches the surface
114
light pollution
extra light washes out the faint objects
115
bad seeing
- 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
resolution
- refers to how sharp images are, the smallest distinguishable features
- the smallest angle we can resolve
117
how is resolution measured
- 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
adaptive optics
- 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
integration time
how long the detector is open/observing
120
charge-coupled device (CCD)
the detector that sorts visible light
121
Infrared observation challenges
- 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
spectroscopy
investigation and measurement of spectra
123
radio
encodes sound into waves in the radio part of the spectrum
124
radio telescope
- 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
Interferometry
- combine the light collected by more than one telescope
- The longer the wavelength, the worse the resolution (for a given size dish)
126
interferometer array
- 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
radar
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
what waves don't reach the earth's surface?
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
the largest airborne IR telescope
Stratospheric Observatory for Infrared Astronomy (SOFIA)
130
major space-based IR telescopes
- IR Astronomical Satellite (IRAS)
- Spitzer Space Telescope
131
Hubble Space Telescope (HST)
2.4-m telescope designed for visible-light observations (and a little IR and UV sensitivity, too)
132
Hubble Ultra-Deep Field (HUDF)
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
what wave observations must be done in space?
UV, x-ray, and gamma-ray observations must be done in space
134
grazing incidence
where x-rays come in and hit the mirror nearly parallel to the mirror so that they actually reflect
135
how can we “observe” gamma rays from the earth’s surface
- 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
