Download Astronomy 10B Study Guide – by Chapter

Astro 10B Study Guide rev. 1/26/2007
Astronomy 10B Study Guide – by Chapter
Know all of these points and you will do well
PROLOGUE (& THE GAS LAW)
What is Astronomy?
Scientific Study
Everything in the Universe – plus the Universe itself
Planets, stars, comets, galaxies, black holes, etc
Matter, energy, space and time
Origins are in Astrology – but Astronomy is a science; Astrology is not
Many astronomers really hate Astrology, but they have no sense of humor!
What is Science?
The purpose of science to produce explanations, models or theories
The scientific method (not the simplified one everyone knows)
Definitions of terms (e.g. theory, hypothesis, prediction, etc)
Philosophical underpinnings of science
Scientific Notation
The Gas Law (PV = nRT)
Almost all matter in the universe is the form of Gas or plasma
Definitions of pressure, volume, number, temperature, Kelvins, density
Playground analogy
The other version of the Gas Law, which is more useful to us: P = ρT
Equation of State tells us how a change in P or ρ changes the other
CHAPTER 1.
Night Sky – looks dome-shaped
Definition of terms (e.g. zenith and horizon)
Sky all rotates from East to West → Earth rotates opposite direction
Constellations
The Celestial Sphere
Definitions of terms (e.g. celestial equator, ecliptic, north celestial pole)
Coordinate system of the celestial sphere (RA & Dec)
North Star directly above Earth’s North pole + circumpolar stars
How does the North Star tell you your latitude?
Solar System View
Sun is at center of solar system
all planets orbit around in nearly a plane (which explains the ecliptic)
All planets orbit in the same direction (CCW as seen from NCP)
Most planets spin in the same direction (CCW as seen from NCP)
Astronomical Unit is the distance from the Earth = 9.3x108 mi (1.5x109km)
CHAPTER 2 – KEPLER’S & NEWTON’S LAWS (IMPORTANT!)
Kepler's laws (true for most all orbits – not just solar system)
K1: First law orbits are ellipses, w/ sun at one focus
definition of eccentricity, focus, etc (What’s eccentricity of Earth’s orbit?)
K2: Second law says planets sweep equal area in equal times
Planets speed up when in the part of the orbit nearest the Sun
K2 is equivalent to conservation of angular momentum
K3: Third law is the equation: P2 = k D3
Planets with bigger orbit size have much bigger orbital periods
Used to find mass of objects with satellites because k = 1/(m1 + m2)
Newton’s laws of motions
Definitions of velocity, speed, direction, mass, and acceleration
N1: Law of inertia - objects stay at constant velocity unless acted upon by a force
N2: F = ma
This gives us the definition of force – it is that which causes change in V
N3: Law of action-reaction
Normal version is confusing for our purposes
My version:
Forces act between 2 bodies, pulling them together or pushing them apart.
If an object is traveling in a perfectly circular path at a uniform speed is there
necessarily a force involved?
Newton's law of gravity: F = G M1 M2 / R2
Definition of terms: force, mass, distance, etc
Force of gravity increases when either mass increases
Force of gravity decreases when distance increases
Newton showed what relationship between the Moon and an apple?
Which falls faster a heavier object or a lighter one?
CHAPTER 3 - EARTH, MOON AND SKY
Reasons for the Seasons
The #1 wrong reason, changes in the Sun-Earth distance
Flawed because we’re closest to Sun in January
Flawed because seasons are flipped in N-S hemispheres
The right reason: tilt (it is more complicated but it is right)
The tilt changes the hours of sunlight over the course of a year (how?)
The tilt changes the angle the sunlight hits the ground (how spread out it is)
If you don’t know the reasons for the seasons, who was your astronomy instructor?
Phases of the Moon
Definitions (e.g. new, full, crescent, gibbous, waxing, waning and terminator)
Explanation for lunar phases (Sun illuminates it, we see it from dif angles)
Time of moonrise
depends on phase
50 minutes later each successive day
Solar eclipse happens only during New Moon, Lunar eclipse – Full Moon
Solar and Sidereal Days
Mean Solar Day is 24h and 361o
Sidereal Day is 23h56m and 360o
Explanation, Earth orbits Sun as it spins
Stars rise 4minute earlier each successive night
Winter and Summer constellations
Tides
Differences in the strength of gravity in near & far side – stretches planets, etc
Moon and Sun both cause tides
Spring tides and Neap tides
CHAPTER 4 – LIGHT, RADIATION AND SPECTRA
Electromagnetic Waves
Definitions (Electricity, Magnetism, wavelength, frequency, etc)
Electricity + Magnetism = Electromagnetism
E fields and M fields can cause waves EM waves (AKA light, EM radiation)
Equation: λf = c (if you know λ or f you can find the other)
The Electromagnetic Spectrum
They are all light: Radio, IR, Visible, UV, X-ray, Gamma-Ray
The only difference is light with different λ interacts w/ matter differently
Photons: packets of energy
E = fh
So Low E → low f → long λ
Cannot measure wavelike and particle-like properties of light at same time
Atomic Structure
Nucleus
Protons – number of which tells us which element it is
Neutrons – number of which tells us which isotope it is
Has almost all of the mass of an atom
Electron cloud
Electrons – number of which tells us the ionization state of the atom
Cloud is divided into orbitals – each with its own energy level
Atomic Spectral Lines
An electron has to have exact energy to inhabit an orbital
All transitions between orbitals require exact changes of energy
Each element only emits/absorbs photons w/ specific energies
We use these spectral lines to learn the composition of stars, etc
We use these lines w/ Doppler & Zeeman effects to learn other things, too
Types of Spectra
Bright Line Spectrum (Emission line spectrum)
Shows the atomic spectral lines bright
Comes from a gas
Continuous Spectrum
Shows all the colors of the rainbow, unbroken
Comes from solids, liquids and dense gases
We can measure temperature of objects with λmax • T = 3x106 nm•K
Dark Line Spectrum (Absorption line spectrum)
Atomic spectral lines dark, against continuous spectrum background
Comes from gases in front of solids, liquids or dense gases
Astro 10B Study Guide rev. 1/26/2007
Which spectrum does the Sun have? The Moon? A Neon sign? etc
Energy Transport in the Sun
Doppler Effect
Radiative zone – a few 100,000 years
It affects sound waves as well as light waves
Convective zone – a few months
If light source is coming toward you, wavelength, λ is reduced (blue shift)
From Sun to Earth 500 seconds
If light source is going away from you, wavelength, λ is increased (red shift)
Helioseismology (studying the Sun by looking at its sound waves)
The amount of shift (Δλ) is proportional to the speed of the light source
Five minute oscillations – resonances of the Sun
Δλ/ λ = v/c
Detect these sound waves by watching the photosphere bounce up & down
If moving at an angle (not directly toward or away) shift doesn’t give true speed
By comparing different resonant frequencies we can probe inside the Sun
True speed is a combination of line-of-sight speed and tangential speed
Compare to embassy spying analogy
To determine true speed we need to either:
Helioseismology has taught us many things including these
Determine the angle somehow
Rotation of the solar interior
Measure both LOS speed and tangential speed
Temperature of solar interior
Deep within the Sun
just beneath sunspots
CHAPTER 6 THE SUN – EARTH CONNECTION
Motions of the plasma inside the Sun
Solar Composition
Convection
Hydrogen ~90%
Larger ‘rivers’ of plasma within the Sun
Helium ~9%
All else ~1%
Solar Structure
The ‘Atmosphere’ of the Sun
Photosphere is surface – source of the light we see (6000K)
Above that: Chromosphere – Thin, almost transparent/pink (100,000K)
Above that: Corona – Very thin (non-dense) and very hot (1,000,000K)
Above that: The Solar Wind – blows out throughout solar system
The Solar Interior
Photosphere is surface
Below that is the Convective Zone – gets very hot and dense (varies)
Below that is the Radiative Zone – gets hotter and denser
Below that is the Core – extremely hot and dense
Nuclear fusion occurs here because > 12,000,000K
Solar Magnetism
The plasma moves along magnetic fields like beads on a string
Plasma cannot ‘cross’ magnetic fields lines
We measure magnetism using the Zeeman effect
Magnetic fields cause a number of phenomena
Sunspots – darker and cooler than regular photosphere
Plages – brighter, spider-web like things
Flares – X-ray explosions more powerful than 1,000,000 H-bombs
Can injure astronauts in space
Can damage spacecraft
Also release bursts of high speed electrons and protons
Coronal Mass Ejection’s (CME’s) – ejections of hot plasma
Sometimes they have magnetic fields
These mag fields can tangle with Earth’s causing blackouts
Often cause Aurora Borealis
Can damage spacecraft
Prominences – loops of magnetic fields sticking up from the Sun
We can see them because the stick off to the sides
We can see them because the hot plasma moves
The Solar Cycle
There is an 11-year cycle for magnetic activity on the Sun
All magnetic phenomena follow this cycle
We have observed this for ~400 years
By indirect means we can study it farther back
The Sun produces a tiny but extra energy when at a maximum
In mid 1600’s the solar cycle disappeared - Maunder Minimum
The Little Ice Age happened around the same time as this
There is still some debate whether the two are linked
CHAPTER 7 THE SUN – NUCLEAR ENERGY
Nuclear Fusion
The Proton-Proton chain
Three step process
The CNO cycle (not as important in the Sun, but important in bigger stars)
Six step process
Mass-Energy Conversion E = mc2
The Sun turns 4x106 tons of matter into Energy per second
The Sun turns 6x108 tons of Hydrogen into Helium per second