Astronomy 161 -- Autumn 2009 -- Prof. Gaudi Final Study Guide The final will be comprehensive, covering everything in the course. This includes: Unit 1: Introduction Unit 2: Time and the Sky Unit 3: Rise of Modern Astronomy Unit 4: The Physics of Astronomy Unit 5: The Earth and the Moon Unit 6: The Solar System The breakdown of the questions will roughly follow the amount of time spent on each Unit. However, this will only be roughly true. Below I've supplied a study guide that outlines (briefly) the basic material from the course. Please note, this is to serve as an outline and a guide only. There may be questions on information presented in the lectures but not mentioned below. In other words, just because a topic isn't mentioned in this guide does not necessary mean there will not be a question on the quiz about that topic. Caveat emptor. Good luck! Unit 1: Introduction -------------------- -------------------- Lecture 2: Astronomical Numbers ------------------------------- Scientific Notation -Express numbers using powers of 10 (i.e. 0.00015 = 1.5 x 10^-4) -Standard Prefixes (kilo-, mega-, etc) (i.e. 1 Gigayear = 10^9 years) Metric System of Units -Units of Length -Units of Time -Units of Mass -Weight versus Mass mass is a measure of the amount of matter weight is the force of gravity on an object mass is independent of location Lecture 3: The Starry Night --------------------------- There are roughly 6000 stars are visible to the naked eye Constellations -Figures drawn in the sky by connecting stars -There are 88 modern constellations Uses of Constellations: -Cultural Roles -Navigational Aids -Calendars Asterisms -Familiar groupings of stars that are not official constellations -Examples: the Big Dipper, Little Dipper Star Names -The brightest star is alpha -alpha Orionis it the brightest star in Origin (Betelgeuse) Lecture 4: Measuring the Earth ------------------------------ The Spherical Earth -Appeal to perfect symmetry -Demonstration by Aristotle using shadows on the moon Measuring the Earth's Circumference: -Eratosthenes of Cyrene (using the angle of the sun from two different locations) -Claudius Ptolemy Lecture 5: Mapping Earth & Sky ------------------------------ Angular Units: -Degrees (º), Minutes ('), & Seconds of arc ('') Terrestrial Coordinates: -Longitude & Latitude Celestial Sphere: -Celestial Poles (projection of Earth's rotation axis onto the celestial sphere) -Equator (projection of the Earth's equator onto the celestial sphere) -Declination -Local Horizon & Zenith The Angle Between the North Celestial Pole and the North Compass Point on the Horizon is your Latitude! Lecture 6: Daily and Annual Motions ----------------------------------- Daily Motions -Reflection of the Earth's Daily Rotation (stars, moon, sun, rise in the east and set in the west) Circumpolar Stars (stars that are always above your local horizon) Annual Motions -Reflection of the Earth's Orbital Motion -Ecliptic: The Path of the Sun (sum slowly moves west to east relative to the stars) (tilt of ecliptic relative to the equator: 23.5 degrees) (also called the obliquity of the ecliptic) Solstices & Equinoxes -When the sun is on the equator Lecture 7: The Four Seasons --------------------------- The Four Seasons -Due to the tilt of the Earth's axis relative to the plane of its orbit. -NOT due to changes in the distance of the Earth from the Sun!!! The tilt of the Earth's axis affects -The amount of direct sunlight (Insolation) -The length of the day Lecture 8: The Phases of the Moon --------------------------------- The Moon always keeps the same face towards the Earth. -Rotation and Revolution are synchronous. -or, rotation period and period around the Earth are the same -the moon does rotate! Phases of the Moon: -Fraction of the sunlit side visible to us. -full: moon opposite the sun (moon rises when sun sets and vice versa) -new: moon on the same side as the -quarter: moon at a 90 degree angle from the sun Lunar Sidereal Periods: 27.3 days Lecture 9: Eclipses of the Sun and Moon --------------------------------------- Lunar Eclipses -Moon passes through the Earth's shadow -Full moon -Total, Partial, & Penumbral lunar eclipses Solar Eclipses -Earth passes through the Moon's shadow -New moon -Total, Partial, & Annular solar eclipses If the Moon's orbit were exactly aligned with the Ecliptic, we would see -A solar eclipse every New Moon -A lunar eclipse every Full Moon But, this clearly does not happen. Why? -The moon's orbit is tilted ~5° from the Ecliptic. Lecture 10: Telling Time ------------------------ Timekeeping is tied to Astronomy Divisions of the Year: -Quarter & Cross-Quarter days -Months & Weeks Divisions of the Day: -Hours, Minutes & Seconds Solar & Sidereal Time Civil Timekeeping & Time Zones Lecture 11: The Calendar ------------------------ Our calendars are based on the motions of the Sun and Moon. Types of Calendars: Lunar Calendars Solar Calendars The Julian & Gregorian Calendars Lecture 12: The Wanderers ------------------------- The Planets: -"Wandering stars" that follow complex paths near the Ecliptic. Planetary Configurations: Inferior Planets: Mercury & Venus Appear to follow the Sun across the sky. <28° for Mercury <47° for Venus. Superior Planets: Mars, Jupiter, & Saturn -All move along the Ecliptic on paths seemingly independent of the motions of the Sun. -All can appear in the sky any time (e.g., around midnight) Inferior Planet Configurations Inferior Conjunction -Planet is between the Earth and the Sun. Superior Conjunction -Planet on the other side of the Sun from Earth. During either conjunction, the inferior planet appears to rise and set with the Sun. Maximum Eastern Elongation -Planet is at its furthest East of the Sun as seen from the Earth -Rises & sets after the Sun Maximum Western Elongation -Planet is at its furthest West of the Sun as seen from the Earth -Rises & sets before the Sun Superior Planet Configurations Opposition -Planet is opposite the Sun in the sky. -Rises as the Sun sets -Highest in the sky at midnight. Conjunction -Planet is on the same side of the sky as the Sun. -Rises with the Sun -The planet does not appear in the the night sky. Eastern Quadrature -Planet at right angles to the Earth-Sun line. -Planet rises at noon, sets at midnight. Western Quadrature -Planet at right angles to the Earth-Sun line. -Planet rises at midnight, sets at noon. In general, the planets move eastward relative to the "fixed" stars. Sometimes, however, the planets appear to -Slow down and stop -Start moving westward, or RETROGRADE, -Slow down and stop again, -Resume moving eastward again. Lecture 13: Greek Astronomy --------------------------- Struggle to understand motion of heavenly bodies. Greek Astronomers Anaximander -Among the first to suggest a geocentric (Earth-centered) system Pythagoras -Spherical earth, concentric crystalline spheres Eudoxus -27 nested spheres in circular motion, combined to give retrograde motion Aristotle -55 crystalline spheres within spheres -uniform circular motion -Earth a sphere fixed and unmoving at the center of the Universe -natural state on Earth was rest -natural state of Heavens is uniform circular motion Aristarchus -one of the first to propose a heliocentric system -likely due to his inference that the Sun is larger than the Earth Hipparchus -Introduced epicycles Ptolemy -40 epicycles and deferents. -Equants and eccentrics for all planets, the Moon, and Sun -Provided accurate predictions of the motions of the planets, Sun, and Moon. -Was to prevail virtually unchallenged for nearly 1500 years. Lecture 14: The Revolutions of Nicolaus Copernicus -------------------------------------------------- Copernicus' Heliocentric System: -Earth rotates on its axis once a day. -Earth & Planets revolve around the Sun. -Retained epicycles, but purged Ptolemy's equant -Restoring uniform circular motion. Scientific Objections to Copernicus' model: -"Impossibility" of a moving earth -Non-observation of stellar parallaxes Lecture 15: Tycho Brahe & Johannes Kepler ----------------------------------------- Tycho Brahe -Superb observer who amassed 20 years of precise data on the positions of the planets Johannes Kepler -Brilliant theorist who analyzed Tycho's data -Kepler's Three Laws of Planetary Motion: 1st Law: Orbits are Ellipses with Sun at one focus. 2nd Law: The line joining the Sun and the planet sweeps out equal areas in equal times. 3rd Law: (Period)^2=(Semi-major Axis)^3 Lecture 16: Galileo Galilei & The Telescope ------------------------------------------- Galileo Galilei was the first modern astronomer. Important Discoveries with the telescope: -Moons of Jupiter -Phases of Venus -Craters and Mountains on the Moon -Sunspots Lecture 17: Isaac Newton & The Laws of Motion --------------------------------------------- Newton's Laws of Motion 1st Law of Motion: -Every body will stay in a state of rest or uniform motion in a straight line unless that state is changed by forces impressed upon it. 2nd Law of Motion: -Acceleration is proportional to the force & inversely proportional to the mass (F=ma) 3rd Law of Motion: -To every action there is an equal an opposite reaction. All motion is composed of two parts: -Speed (how fast is it going) -Direction (where is it going) The combination is called the velocity: Change in velocity is acceleration: -Measures how fast the velocity changes. -Change can be in speed, or direction, or both! Lecture 18: Newtonian Gravity ----------------------------- Law of Falling Bodies (Galileo) -In the absence of air, heavy objects and light objects fall at the same, constant rate of acceleration. Law of Universal Gravitation (Newton) -Gravity is an attractive force between all pairs of massive objects -Gravitational force is proportional to the masses, and inversely -proportional to the square of the distance between them. Lecture 19: Orbits ------------------ Newton generalized Kepler's laws to apply to any two bodies orbiting each other First Law: -Orbits are conic sections with the center-of-mass of the two bodies at the focus. Second Law: -angular momentum conservation. Generalized Third Law that depends on the masses of the two bodies. Circular Velocity -Velocity needed to sustain a circular orbit of a given radius Escape Velocity -This is the minimum velocity required to have a parabolic orbit starting at a given distance from a massive body. Lecture 20: Tides ----------------- Tides are caused by differences in the gravitational pulls of the Moon and Sun between near and far sides of the Earth. The Sun also raises tides on the Earth: -The difference between the gravity force on the day and night sides of the Earth are about half that due to the Moon. -Although the Sun is more massive than the moon, it is much further away, and thus its tides are smaller Tidal Effects: -Tidal Locking of the Moon -Tidal Braking slowing the Earth's Rotation -Lunar Recession (increasing size of the Moon's orbit) Lecture 21: Rotation and Revolution of the Earth ------------------------------------------------ The Coriolis Effect -Deflection of a projectile due to the Earth's Rotation: Fire a cannonball due North from a cannon on the Equator. -The cannon is moving east with the Earth's rotation -The cannonball retains its initial, faster, eastward speed as it flies north -The further north it flies, the slower the eastward motion of the Earth's surface beneath its flight. -Result is a slight eastward deflection of the cannonball from its original northward trajectory. Foucault Pendulum -The steady clockwise shift of the pendulum's swing is being caused by the rotation of the Earth. Lecture 22: Light ----------------- Light is an electromagnetic wave, also a particle (photon) -Characterized by the speed and wavelength or frequency -frequency = speed of light/wavelength -higher energy, smaller wavelength, higher frequency -smaller energy, larger wavelength, lower frequency Arrange light in wavelength: spectrum Shortest wavelength to longest wavelength: -Gamma rays, X-rays, UV, visible, infrared, radio Brightness is proportional to luminosity and inversely proportional to distance squared Doppler effect: -Moving away: longer wavelength, smaller frequency -Moving towards: shorter wavelength, larger frequency Lecture 23: Matter ------------------ Matter is composed of atoms: nucleus and electrons Nucleus composed of protons and neutrons Element: # of protons Isotope: same # of protons, different # of neutrons Radioactivity: unstable isotopes, characterized by half-life Half-life: time for half of a radioactive element to decay. Lecture 24: Light and Matter ---------------------------- Temperature sets the energy content, speed of the particles A blackbody is an object that absorbs all light. -Absorbs at all wavelengths. -As it absorbs light, it heats up. -characterized by its Temperature. -Emits at all wavelengths (continuous spectrum) -Energy emitted depends strongly on the Temperature. -Energy per unit area is proportional to Temperature to the fourth power -Peak wavelength is inversely proportional to temperature (Wein's law) Lecture 25: Spectroscopy ------------------------ Electrons cannot orbit just anywhere around a nucleus: -Can only orbit in discrete orbitals. -Each orbital corresponds to a particular energy of the orbiting electron. -If an electron does not have exactly the right energy it cannot be in that orbital (all or nothing). -The details are dictated by quantum mechanics. Emission lines: -When an electron jumps from a higher to a lower energy orbital, a single photon is emitted with exactly the energy difference between orbitals. Absorption Lines: -When an electron absorbs a photon with exactly the energy needed to jump from a lower to a higher orbital. Absorption is very specific: -Only photons with the exact excitation energy are absorbed. -All others pass through unabsorbed. Every atom, ion, molecule has a unique spectral signature Spectra allow us to determine the properties of distant objects Lecture 26: Telescope --------------------- Modern optical telescopes are reflecting The light collecting area of a telescope is proportional to the primary lens diameter squared Resolution limited to atmosphere on the ground Optical, radio can be observed from the ground Other wavelengths must be observed space Lecture 27: The Age of the Earth -------------------------------- Age of the Earth Earth is roughly 4.5 billion years old Determined using radiometric dating Solar system, Earth, Moon formed roughly the same time (within several 100 million years ago) Lecture 28: The Interior of the Earth ------------------------------------- Layer-cake structure due to differentiation -internal structure revealed by the propagation of seismic waves from Earthquakes through the interior Solid inner core, molten outer core, thick mantle, thin crust Internal latent heat, but primarily from radioactivity Magnetic field: -Caused by the geodynamo, which requires: Molten interior (conduction), convection, and rotation Crust broken up in to plates Plates move due to mantle convection (unique to Earth) Earthquakes, volcanoes occur near plate boundaries Lecture 29: The Atmosphere of the Earth --------------------------------------- Nitrogen, Oxygen, Argon, Water Vapor No Hydrogen and little Helium Temperatures set by solar radiation and Greenhouse Effect Carbon dioxide is scrubbed out of the atmosphere by rain: -Locked up in oceans, rocks Oxygen (and Ozone) came from life Lecture 30: The Moon -------------------- Surface of the Moon: -Old, heavily cratered highlands -Younger, dark Maria -Thick regolith of pulverized rock Interior of the Moon -Crust and Mantle, but no Core(?) -No magnetic field today The Origin of the Moon -likely formed from a giant impact Lecture 31: Overview of the Solar System -------------------- The Solar System contains: -The Sun (99.9% of the mass) Terrestrial Planets -Mostly rock and metal, high density -Distance: Mercury, Venus, Earth, Mars -Mass, Radius: Mercury, Mars, Venus, Earth -Atmosphere: Mercury, Mars, Earth, Venus -Located within 0.3-1.5 AU Jovian Planets -Mostly hydrogen and helium, low density -Distance: Jupiter, Saturn, Uranus, Neptune -located within 5-30 AU The planets all lie in nearly the same plane and orbit in the same general direction. Lecture 32: Origin of the Solar System -------------------------------------- Planet formation: -Gas cloud contracts, heats up, spins faster Condensation of grains & ices versus distance -light elements (i.e. ices) condense a lower temperatures far from the Sun -Inside-out: Oxides, iron-nickel, silicates, ices -Thus different compositions of inner and outer planets -Little water, methane, etc on terrestrial planets From Planetesimals to Planets: -Small grains into planetesimals into planets Lecture 33: Mercury ------------------- Mercury is the innermost planet Rotation in a 3:2 resonance with Sun, measured with radar, tidally locked Surface, heavily cratered (first ~billion years), virtually no atmosphere Interior, large iron core & weak magnetic field -large iron core may be due to a giant impact which stripped the mantle Lecture 34: Venus ----------------- Venus is the second planet from the Sun Nearly the same size and mass as the Earth Slow retrograde rotation -May also be due to a giant impact Hot, heavy CO2 atmosphere -likely caused by a runaway Greenhouse effect -leads to the hottest surface temperature of any terrestrial planet -all of Venus' carbon dioxide is in the atmosphere, no water to scrub it out of the atmosphere Sulfuric acid clouds Surface: mapped using Radar, rolling plains, highlands & valleys Lecture 35: Mars ---------------- Mars is the fourth planet from the Sun About half the size of Earth Thin, dry CO2 atmosphere -atmospheric pressure too low for liquid water Evidence for liquid water on the surface in its early history Lecture 36: Terrestrial Planets in Comparison --------------------------------------------- Surfaces & Interiors depend on size: -Small bodies (Mercury, Mars, & Moon) have old surfaces & cold interiors -Large bodies (Venus & Earth) have young surfaces & hot interiors Atmospheres: -All start with substantial atmospheres -Retention of atmosphere depends on temperature and escape velocity -Small, hot planets lose atmospheres faster Evolution driven by the greenhouse effect -Venus carbon dioxide in atmosphere -Earth in oceans and rocks -Mars in atmosphere, but most atmosphere lost (small size) Lecture 37: Jupiter and Saturn ------------------------------ Jupiter & Saturn are the largest Planets -Giant Gas Planets -Rotate very quickly (Jupiter fastest), so appear flattened Cloud Features: -Colored Belts & Zones -Strong Cyclonic Storms (Great Red Spot) Atmosphere & Internal Structure: -Mostly Hydrogen & Helium -Interior contains metallic hydrogen due to high pressure -Dynamo generates a large magnetic field (Jupiter's is the largest) Radiate more energy than they get from the Sun (from gravitational contraction) Lecture 38: Uranus and Neptune ------------------------------ The outermost of the planets, Ice Giants -Green in color due to methane, which absorbs red light -Nearly identical structure & composition. -Contain mostly rock and ices -Much less hydrogen and helium than Jupiter and Saturn -Differences due to distance from the Sun Uranus: -Lacks internal heat and so nearly featureless -Axis tilted by 98 degrees, results in extreme seasons -Axial tilt may be due to a giant impact Neptune: -Has internal heat and an active atmosphere Lecture 39: Moons of Jupiter ---------------------------- Jupiter has 63 known moons -4 Galilean Moons: -Io, Europa, Ganymede & Callisto. -Ganymede is the largest satellite of any planet Large (>3000 km), spherical & differentiated -Io is volcanically active. Europa may have an ocean below the ice. 59 Small Moons: -Small (<200 km), irregular, & undifferentiated Lecture 40: Moons of Saturn --------------------------- Saturn has 56 moons and bright rings -1 Giant Moon: Titan 55 Smaller Moons, mostly icy -Those >300km diameter are round Enceladus -Young surface with water-ice geysers -Active volcanism Titan -Thick Nitrogen & Methane atmosphere -Lakes of liquid Methane Lecture 41: Planetary Rings --------------------------- All Jovian planets have rings: -Jupiter: faint, dusty rings -Saturn: bright, spectacular rings -Uranus: dark, thin rings -Neptune: dark, thin rings & ring arcs Ring properties: -Composed of many small bodies -Constantly colliding with one another Shepherd moons -confine the ring particles -create gaps and thin rings Lecture 42: Asteroids, Meteoroids, Meteors, and Meteorites ---------------------------------------------------------- Asteroids: -Small bodies in the inner solar system Asteroid Belt between Mars & Jupiter. -Orbits are strongly influenced by Jupiter. Made of rock, metal, or a mix of the two. Meteoroids: -Bits of rock & metal orbiting the Sun. -Seen as meteors in the sky, or collected as meteorites on the ground Lecture 43: Icy Worlds of the Outer Solar System --------------------------- Triton: -Neptune's giant moon -Probably a captured Kuiper belt object -Young surface with cryovolcanism & geysers Pluto & Eris -Dwarf Planets -Very similar to Triton in their properties Trans-Neptunian Objects, or the Kuiper Belt: -Family of icy bodies orbiting beyond Neptune -largest are Pluto and Eris -leftover 'construction debris' of solar system formation Lecture 44: Comets and the Oort Cloud ------------------------------------- Icy visitors from the outer solar system Comets have long elliptical orbits -Short- & Long-period comets. -Origin in the Kuiper Belt & Oort cloud. Structure of Comets -Nucleus & Coma -Dust & Ion Tails -Basically are "Dirty Snowballs" Lecture 45: Is Pluto a Planet? ------------------------------ Addition of New Planets: -Discovery of Uranus by William Herschel -Discovery of the Asteroids -Were temporarily planets, but later demoted -Prediction & Discovery of Neptune Discovery of Pluto by Clyde Tombaugh -was called a planet, but this was controversial -nothing else was found in this region for a long time so Pluto's status was not questioned. Discovery of Eris in 2005 meant that the definition of a planet had to be reconsidered. 2006 IAU Definition of Planets & Dwarf Planets A planet is any celestial body that, within the Solar System, 1. is in orbit around the Sun, and not a satellite of another planet. 2. has sufficient mass for its self-gravity to assume a spheroidal shape 3. has cleared its orbital neighborhood Pluto demoted to "Dwarf Planet" status Lecture 45: Search for Life in the Universe ------------------------------------------- Habitable planet is defined by: -Its distance from its parent star (habitable zone) -Its size Conditions for life: -Stable, long-lived energy source -Elements of life (water, carbon, etc) -Benign environmental conditions -A location for life to arise Stars with rocky planets in their habitable zones are the best places to look for life. Planets are hard to find -Radial velocity method has discovered the most planets. -Total number of planets is of order 250 and growing Detecting life on other planets -Spectra allow us to detect signatures of life on distant planets. Lecture 46: Death in the Universe --------------------------------- The Sun is getting brighter, -Thus the Earth is getting warmer -In 1 Gyr, moist greenhouse may be triggered -In 4.5 Gyr, the runaway greenhouse will be triggered -In 6.5 Gyr, the Sun will run out of hydrogen -Without additional energy sources, life in the solar system will be difficult or impossible. The Universe is Expanding and Accelerating -No other galaxies will be visible Five Ages of the Universe, last era is the dark era -After the dark era (10^100 years), life likely becomes impossible. THE END