Final Exam Flashcards
(90 cards)
1
Q
Angular Distance v.s Angular Size
A
- Angular Distance is the fraction of the night sky that is between two objects
- Angular Size is the measure of an object using an angle. The closer the object the larger the angular size, the farther the object the smaller the angular size
2
Q
Pythagoras
A
- Used math
- Perfectly spherical and unchanging
- Earth is still and all celestial bodies move through the crystalline sphere around it
3
Q
Celestial Sphere and Constellations
A
- Used as a convenient descriptor
- RA Right Ascension measure in hours. 1 HR is equal to 15 degrees. 360/24. similar to longitutde
- Declination measure in degrees similar to latitude
- Constellation is a human grouping of stars in the night sky in to recognizable pattern
4
Q
Zenith
A
-Imaginary point directly above your location on the celestial sphere
5
Q
Aristotle
A
- Circular motion natural motion of the universe
- Physical phenomenon with paradigm
- FIRST EXAMPLE OF SCIENTIFIC METHOD
- Eclipses: lunar= sun earth moon, solar= sun moon earth
- Earth isn’t flat because the shadow cast on the moon is circular
6
Q
Scientific Theories
A
-Must be testable, continually tested and simple
7
Q
Diurnal Motion
A
-Sun rises in the East and sets in the West with a westward motion but some stars do not go below the horizon.
8
Q
Circumpolar Stars
A
- Never ‘rise or set’
- North Star Polaris, used to define the rotational axis of the celestial sphere
9
Q
Retrograde Motion
A
- Sun appears to change position slightly with respect to stars
- Backward loop, eastward motion appears to move westeward because everything is moving at different speeds
10
Q
Ecliptic
A
- Sun’s own path across the sky
- Planets and moon move close to ecliptic
- Signs of the Zodiac on the ecliptic
- Furthest north during the summer solstice (longest day)
- Furthest south during the winter solstice ( shortest day)
11
Q
Vernal and Autumnal Equinox
A
- Ecliptic crosses the celestial equator
- Equal day or night
- Rises directly East and Sets directly West
12
Q
Summer and Winter Solstice
A
- Occur when the sun is at its highest position of sunrise
- Furthest North at summer solstice
- Furthest south at winter solstice
13
Q
Moon Phases
A
-Sun–New Moon (invisible)–Waxing Crescent–Quarter Moon–Waxing Gibbous–Full Moon (SEM)–Waning Gibbous–Third Quarter-Waning Crescent
14
Q
Lunar Eclipse
A
- Sun–Earth– Full Moon (full)
- Doesn’t happen every time because the moons orbit is tilted slightly relative to the ecliptic
15
Q
Solar Eclipse
A
-Sun–New Moon– Earth
16
Q
Why the Seasons
A
- Earth axis is tilted
- It is about angle not distance
- Earths revolution around the sun due to the inclination of the axis
17
Q
Parallax
A
- Apparent displacement of a foreign object as the observers location changes
- Parallax shift is inversely proportional to the distance
- Small parallax large distance
- Large parallax small distance
18
Q
Aristarchus
A
- First to adopt the sun as the center of the universe
- Based on the geometric assumption that the sun is larger than the Earth and thus it is more natural for the Sun to be at the center
- No evidence
- HELIOCENTRIC
19
Q
Hipparcus
A
- Rejected the heliocentric model because he could not observe stellar parallax
- Invented trig, found moons distance and the length of the year
- Made accurate predictions possible
20
Q
Ptolemy
A
- Model of planetary motion using epicycles and deferents
- Epicycles are the smaller circles that travel on deferents which are the larger circles
- Incredibly accurate
21
Q
Corpernicus
A
- Breaks paradigm
- Went back to Aristarchus heliocentric
- No observational evidence-Circular orbits
- Retrograde motion: speed of orbit decreases with distance from the sun, brightness of planets
22
Q
Tycho Brahe
A
- New instruments, extremely accurate
- Rejected heliocentric model for lack of evidence: parallax and couldn’t feel the Earth moving
- Record of stars and planets
23
Q
Johannes Kepler
A
- Accepted Copernican helio-centric
- Determined Mars’ orbit was an ellipse
- Developed 3 Laws
24
Q
Kepler’s First Law
A
- All orbits are ellipses with the sun at one focus
- The further apart the focus’ are the flatter the are
- Straight line= 1 Circle=0 (eccentricity)
25
Kepler's Second Law
-A line drawn between the sun and a planet sweeps out equal areas in equal time therefore the speed of an object must change
-Major Axis: long axis of the ellipse
-aphelion: velocity goes down, further from the sun
a(1=e)
-perihelion: velocity goes up, closer to the sun
a(1-e)
26
Kepler's Third Law
- P2=a3
| - The square of planets orbital period is proportional to its orbital distance (semi-major axis) cubed
27
Galileo Galilei
- Heliocentric
- Milky way made up of numerous faint stars
- Moon has craters
- Sun is rotating (moving sun spots)
- Venus has phases like the moon
- Jupiter has moons
- Beefed church by using modern vernacular
28
Newton
- Unified the force of gravity with celestial bodies. Celestial+Terrestrial
- Mathematical not empirical
- Basic laws of motion
29
Newtons First Law
- A moving object will move forever in a straight line unless it is compelled to change that sate by a force acting on it.
- Inertia^^
30
Newtons Second Law
- The change in motion is proportional to the force impressed and is made in the direction of the straight line in which the force is impressed.
- When a force acts on a body of mass it produces in it an acceleration equal to the force/m
31
Newtons Third Law
-To every action there is an equal and opposite reaction
32
Weight v.s Mass
| Gravity
- Weight: force with which gravity pulls you towards the Earth's center
- Mass: total amount of matter an object contains
- Gravity: continues force; an object having mass always exerts a gravitational force on all massive objects
33
Fundamental Forces in Ascending Order
- Gravity
- Weak Nuclear Force
- Electromagnetism
- Nuclear Force
34
Why Are Photons the Only Particle That Can Travel at the Speed of Light?
- Protons have no mass
| - but they do have energy
35
Light Wave Interference
- In phase: add constructively
| - Antiphase: cancel each other out
36
Wavelength
-Distance between two successive crests or troughs
37
Frequency
-The number of crests passing a point in a given time
38
Amplitude
-Distance from middle to crest
39
Wavelength Ranges
- Visible 700-400 nm
- Infrared 700-100 micro
- Radio >100 microns
- UV 0.0004mm-1 nm
- Gamma 1-1x10^-4 nm
40
Blackbody Spectrum
- All objects radiate
- Distribution of energy is called a Planck Curve
- Perfect BB absorbs all energy and remits it all through radiation
- The shorter the wavelength, the greater the frequency and the higher the temperature
41
When an Atom is Struck by a Photon..
- It could have so much energy that it knocks the electron off leaving an ionized atom behind
- If it has exactly the right amount of energy as the difference between two energy levels it could absorb the photon and an electron jumps to a higher energy state (excitation)
- When it returns to the ground state a photon is emitted
- Nothing
42
Spectral Lines
- De-excitation releases photons with certain energies
| - Every set of spectral lines is different, like a fingerprint
43
Continuous Spectra
- Hot star or high density gas/solid
| - ROYGBIV with no interruptions, emission of radiation at all wavelengths
44
Emission Spectra
- Light from nearby star shines on low density gas
| - Emission lines on a black background
45
Absorption Spectra
- Light from nearby shines through a cool, low density
| - ROYGBIV with black gaps where some radiation has been absorbed by gases
46
Kirchoff's Laws
1. Luminous solid/dense object emits light of all wavelengths: continuous
2. Hot, low density gas emission spectra: emission
3. Cool, low density gas absorbs certain wavelengths from continuous spectrum: absorption
47
Molecular Spectral Lines
- Molecules emit electromagnetic, vibrational and rotational
- Detected by radio
48
Bohrs Model of the Atom
1. Ground state is the state of lowest energy where electrons want to be
2. There is a max energy an electron can have before it is no longer bound and becomes ionized
3. Defined orbitals, said to be quantized
49
Cascade Effect
- If there is enough energy to jump to the second excited state the electron can cascade down one orbital at a time emitting two photons with energy equal to the difference between each orbital
- Red emission for hydrogen
50
Doppler Effect
- Sound waves get scrunched up and spread out with movement
- Blue Shorter wavelength Higher frequency Towards
- Red Longer wavelength Lower frequency Away
51
What is a Telescope
- A light bucket that captures as many photons as possible from a given region of the sky
- also magnify and resolve
52
Refracting v.s Reflecting Telescopes
- Refractors use lenses to bend the light beam, hard to make lenses that are supported that large, chromatic abberation
- Reflectors use mirrors , all large modern telescopes are reflectors
53
The Higher the Resolution
-The smaller the number
54
Resolving Power
-Ability to distinguish separate objects in the sky
55
Atmospheric Blurring and Seeing
- Atmospheric turbulence causes twinkling and the illusion of motion
- Seeing are the effects of atmospheric turbulence
56
Telescopes are Placed High Up
-Because of light pollution and to fight atmospheric blurring
57
Active v.s Adaptive Optics
-Active optics are techniques to control environmental and mechanical fluctuations where as Adaptive Optics have to do with changing the shape of the mirror
58
What Does UV
What Does Optical/Near IR
What Does Far Ir/Radio
- UV sees the hottest part of the universe
- Optical/IR sees hot
- Far IR/Radio sees cool gas and dust
59
Radio Telescopes
- Built large because cosmic radio emission is extremely faint
- Large wavelengths
60
Interferometry
-Very long baseline , more than one radio telescope to view the same object for better resolution
61
Layers of the Sun
```
Core
Radiation Zone
Convention Zone
Photosphere: radiation that we see "surface"
Chromosphere
Transition Zone
Corona
Solar Wind
```
62
Proton Proton Chain
- Need a temperature of 10^7 for nuclear fusion so protons can move fast enough to slam in to each other
- Combat electrostatic force
- P+p= deuterium+positron+neutrino
- 4 protons= 4 He + y + 2 neutrinos
- y= gamma rays
63
Larger the Mass of a Star
-The more energy it uses and the shorter it lives
64
Star Order
- Supergiant
- Giant
- Brown/Red Dwarf
- White Dwarf
- Neuron Stars
- Pulsars
- Black Holes
65
Photometry
-Using B and V filters to find the temperature
66
Hertzsprung Russell Diagram
- Luminosity v.s Temperature
| - Top left high luminosity high temp
67
Luminosity Classes
- Measure absorption spectra, the wider the line the denser and smaller it is
- The narrower it is the less dense and larger it is
```
Bright Super Giants Class Ia
Super Giants-Class Ib
Bright Giants-Class II
Giants-Class III
Main Sequence -Class V
```
68
Spectroscopic Parallax
- Using stellar spectra to infer distances
1. Measure apparent brightness and spectral type
2. Use spectral type to find luminosity
3. Inverse square law to determine distance
69
Binary Stars
- Multiple stars in a system, use Doppler shift of spectral lines and orbit
- Eclipsing Binaries: light varies, alternative way to measure stellar radii
- Keplers 3rd Law re-imagined to find mass
70
Distance Ladder
- Earth
- Radar Ranging
- Stellar Parallax
- Spectroscopic Parallax
- Cepheid Period Luminosity Relation
71
Gas and Dust in the ISM
-Unevenly distributed
72
Gas in ISM
- Emits or absorbs radiation
- Made up individual atoms and small molecules
- Low Density
- Similar to star makeup H and He
73
Dust in ISM
- Absorbs and scatters radiation and thus reddens and dims
- Longer wavelengths penetrate
- Dust blocks shorter wavelengths
- Made up clumps of atoms and molecules
- Less dense than ISM gas
- Transparent to radio and infrared
- makeup largely unknown
74
Emission Nebulae
- Regions of glowing ionized gas (HII) at or near the center of newly formed O/B stars producing large UV
- Group of hot young stars within
- Hydrogen Balmer (red)
75
Reflection Nebulae
- Caused by starlight scattered from dust particles in interstellar clouds between Earth and bright stars
- Appear blue because short wavelengths are preferentially scattered
76
Dark Dust Clouds
- Dense and cold
- No nearby stars or emission nebulae
- Absorption line spectra
- Block light from behind
- Observed using radio
77
Electron Spin
- Quantized
- Parallel spin is the lower energy state
- Antiparallel is where a photon is emitted
78
21 cm Radiation
- Rely on low energy radio emission produced by interstellar gas
- Reaches Earth unscattered
79
Molecular Clouds
- extremely large
- cold, higher density and more dusty
- Internal electron transitions produce molecular spectral lines
- Site of current and future star formation
80
Molecular Tracers
- Hydrogen is most abundant but it doesn't emit or absorb
| - Tracer molecules exist in cloud complexes
81
Stage 1 Fragmentation of a Giant Molecular Cloud
- Must fragment in to clumps, forms many stars
- Dense, low temperature must become unstable
- Could be a result of a shock wave that pushes enough mass in to a small region that it begins to collapse under the force of gravity
- Could also be Chaotic Turbulence: small cloudlets that slam in to each other randomly and increase the density and mass
82
Stage 2 Collapse of the Cloud Fragment
- Higher density, becoming more opaque so that radiation cannot escape as easily
- Pressure and temperature rising
- Heated gas wants to expand, works against the collapsing force of gravity
- Pancake effect, gas rotation gets faster, Conservation of Angular Momentum, same as a figure skater
- Flattens
83
Stage 3 Early Protostar and Disk
- Flattened cloud that is collapsing but slower
- Inner region is more dense and hotter
- Outer region cooler and less dense
- Energy from gravitational contraction not fusion
- Rain material onto protostellar surface, mass increases, continues to collapse
84
Bipolar Outflow
- Stage 3- Early Protostar and Disk
- Strong winds directed by disk out the North and South poles
- Eventually form planets or blow away
85
Stage 4 Protostar
- Can now plot HR diagram
- Very luminous but temp not high enough for fusion
- As it gets on the HR diagram, star starts to cool and the temp surface temp remains constant
- Luminosity decreases as protostar shrinks
86
Stage 5 Hyashi Track
- 5: Radius shrinking, T Tauri Phase
- 6: Star is born, temperature 10^7, fustion begins
- Still has not reached MS
87
Time Scale for Formation not on MS
- Larger than Sun- 10^6
- Sun size 50x10^6
- Smaller than sun 10^9
88
Main Sequence Star Characteristics
-Stable gravity and pressure balance
-Stay on MS for few million for Most Massive
-few billion for Solar Type
-Many billion for Low Mass
NEVER MOVE UP OR DOWN MS
89
Formation of a Planet
- Collapsing rotating fragment in to flattened disk (pancake)
- Dust grains facilitate condensation of certain elements
- Condensation nuclei get bigger
- Matter swept up create planets
- takes millions of years
90
How to Detect Planets
- Not directly
| - Spectroscopic wobble
