Astronomy 3: Unit 1
CHAPTER E INTRODUCTION
SECTION E.1 THE “OBVIOUS” VIEW
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Universe > galaxy > planet
Constellations: patterns and relationships between stars when no true connection exists
o Generally stars are not close together
o Stars in a constellation are ranked in order of brightness
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Brightest: α (alpha) / Second Brightest: β (beta)
Celestial sphere: relative position of the starts to each other that we see on earth
o Stars appear to move on sky
Polaris: Pole Star, North Star
Rotation: spin of the earth in orbit
North/South celestial pole: point where Earth’s axis intersects the celestial sphere in the Northern/Southern Hemisphere
Celestial equator: midway between north and south celestial poles
Celestial Coordinates): latitude and longitude of the celestial coordinates
o Declination (latitude) is measured in degrees
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north/south celestial pole = +90°/-90°
o Right ascension (longitude) is measured in angular units
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Hours/minutes/seconds and increases in eastward direction
SECTION E.2 EARTH’S ORBITAL MOTION
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Diurnal motion: apparent daily motion of stars ”through the sky”
o Solar day: amount of time (24 hours) that it takes for the sun go from sunrise/set
o Sidereal day: shift of stars, a day measured by stars (3.9 minutes shorter, +0.9876°)
Ecliptic: elliptical motion of the planets orbiting the sun
o Summer solstice: point on the ecliptic where the Sun is at its northernmost point about the celestial equator (June 21: longest
day of the year)
o Winter solstice: southernmost point from the sun (December 21: shortest day of the year)
o Location determines seasons
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Summer: when the sun is highest above the horizon
Equinox: where the ecliptic intersects the celestial equator (where Earth’s rotation axis is perpendicular to the line joining Earth to the
Sun
o Day and night are of equal duration
o Autumnal equinox: sun crosses from northern into southern hemisphere (September 21)
o Vernal equinox: sun crosses equator moving north (March 21)
o Tropical year: interval of time from one vernal equinox to the next (365.242 solar days)
Tropical year: time required for Earth to complete exactly one orbit around the vernal equinox (385.242 solar days)
Sidereal year: time required for Earth to complete exactly one orbit around the sun (386.256 solar days)
o Precession: Earth’s axis changes its direction over the course of time, although the angle between the axis and a line
perpendicular to the plane of the ecliptic always remains close to 23.5
SECTION E.3 EARTH’S ORBITAL MOTION
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Lunar phases: cycle of moon to complete revolution around Earth
o Month: takes about 29 days to complete
o New moon: not visible
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Wax: grow
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Crescent: as more of moon shows
o Quarter moon: half of the lunar disk is visible
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Gibbous phase: more than half of the lunar disk is visible
o Full moon: completely visible
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Wanes: shrinks
Moon’s orbit is inclined at 5.2°
Synchronous rotation: rotates on axis in exactly the same time it takes to orbit Earth
o moon always keeps the same face towards Earth
o Sidereal month: time required for moon to complete one revolution and returns to starting point on celestial sphere (27.3
days)
o Synodic month: time required for moon to complete a full cycle of phases (29.5 days)
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Because of Earth’s motion around the Sun, the Moon must complete slightly more than one full revolution to return
to the same phase in its orbit
Eclipse: when the Sun, Earth, and Moon line up
o Lunar eclipse: when the Sun and the Moon are in exactly opposite directions as seen from Earth; Earth blocks light from sun
and moon is completely blocked
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Partial eclipse: shadow does not completely cover the moon
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Total eclipse: entire lunar surface is obscured
o Solar eclipse: when the Moon and the Sun are in the same direction as seen from earth; Moon blocks the light from the sun
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Partial solar eclipse: only a portion of Sun’s face is covered
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Total solar eclipse: Sun’s light is completely blocked except for ring
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Corona: Sun’s outer atmosphere
o Umbra: central region of eclipse shadow where all light from source is blocked
o Prenumbra: outer region of shadow where not all light is blocked
o Region of totality: if all light were to be blocked
o Annular eclipse: when only a ring of the sun is visible
SECTION E.4 THE MEASUREMENT OF DISTANCE
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Triangulation: distance-measurement method
Cosmic distance scale: distances in space based on geometric measurements
Parallax: apparent displacement of a foreground object relative to the background as an observer’s location changes
SECTION E.5 SCIENTIFIC THEORY AND THE SCIENTIFIC METHOD
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Scientific method: approach to investigation
o Observation  prediction/hypothesis  theory
o Theory: framework of ideas and assumptions used to explain some set of observations and make predictions about the real
world
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Must be testable
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Must be tested
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Should be simple
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Should be “elegant”
CHAPTER 1 THE COPERNICAN REVOLUTION
SECTION 1.1 THE MOTIONS OF THE PLANETS
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Retrograde motion: backward (westward) travel
Geocentric universe: Earth is the center of the universe and all other bodies move around it (Aristotle 384-322 A.D.)
o Epicycle: small circle in which each planet moves around
o Deferent: large circle in which epicycle orbited on
o Ptolemaic model: map of the motion of planets if Earth were the center (Claudius Ptolemaeus, Ptolemy 140 A.D.)
o (Aristarchus of Samos 310-230 B.C.) all the planets revolved around the sun and that Earth rotates on its axis once a day
Heliocentric model: sun-centered model of the universe (Nicholas Ccopernicus)
o Copernican revolution: realization that Earth is not the center
SECTION 1.2 THE BIRTH OF MODERN ASTRONOMY
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(Galileo Galilei early 1600s) discovered
o Moon has mountains, valleys, and craters
o Sun has imperfections – sunspots and that the Sun rotates approximately once per month around an axis roughly perpendicular
to the ecliptic plane
o Jupiter has four moons
o Venus has a cycle of phases
SECTION 1.3 THE LAWS OF PLANETARY MOTION
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(Tycho Brahe 1546-1601) employer of Kepler
o Made detailed observations
Johannes Kepler
o Laws of planetary motion (Kepler’s Laws)
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I. The orbital paths of the planets are elliptical with the Sun (greatest mass) at one focus
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Eccentricity: distance between the foci / length of major axis
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to describe size and shape of planet’s orbital path, only need semi-major axis and eccentricity
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perihelion: point closest to the Sun
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aphelion: greatest distance from the Sun
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II. An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time
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Period: time needed for a planet to complete one circuit around the Sun
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III. The square of a planet’s orbital period is proportional to the cube of its semi-major axis
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Astronomical unit (AU): average distance between Earth and the Sun
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P² (in Earth years) = a³ (in AU)
o P = planet’s sidereal orbital period; a = semi-major axis
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P² = a³/Mtotal (in solar units)
Radar: radio detection and ranging
SECTION 1.4 NEWTON’S LAWS
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Newtonian mechanics: basic laws of motion. Law of universal gravitation, some calculus to explain and quantify behavior of Earth
o Newton’s first law of motion: unless some external force change sits state of motion, an object at rest remains at rest
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Inertia: tendency of an object to keep moving at the same speed and in the same direction unless acted upon by a
force
o Newton’s second law: the greater the force acting on an object, or the smaller the mass of the object, the greater the
acceleration
o Newton’s third law: every force has an opposite but equal force
Gravitational force: the more massive an object, the stronger its gravitational pull
o
F = Gm1m2/r2
G = 6.67x10-11 Nm2/kg2
o
2
V = GM/r
CHAPTER 2 Light and Matter
SECTION 2.1 INFORMATION FROM THE SKIES
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Electromagnetic radiation: energy and information being transferred without physical connection between two locations
o Visible light: part of EM radiation that human eye can see
o Radio, infrared, visible, ultraviolet, x ray, gamma ray
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Waves: way in which energy is transferred from place to place without physical movement of material from
o Wave period: number of seconds needed for the wave to repeat itself at some point in space
o Amplitude: half of height
o Frequency (in Hz) = 1 / period
o Wave velocity =
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Diffraction: waves “bending around corners”
Interference: crests and troughs of waves from different sources can reinforce or partly cancel one another
How does it travel?
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Water waves, sound waves require a medium (sound, air)
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Radiation does not require a medium
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Information about our particle’s motion is transmitted through space via a changing electric field
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Electric and magnetic fields
o Disturbance produced by moving charge consists of oscillating electric and magnetic fields,
oriented perpendicular to one another and moving together through space
o Speed of light = 3x105km/s
SECTION 2.3 THE ELECTROMAGNETIC SPECTRUM
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Visible light is between 4.3x1014 nm (red) – 7.5x1014 nm (violet)
o Smaller wavelength, higher frequency
Opacity: extent to which radiation is blocked by the material through which it is passing (air)
SECTION 2.4 THERMAL RADIATION
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Temperature: measure of the amount of microscopic motion within it
o Hotter the object, higher temperature, faster moving particles, more energy radiated
Intensity: amount or strength of radiation
Blackbody: an object that absorbs all radiation falling upon it
Connection between frequency/wavelength and temperature
o Wien’s Law: Wavelength of peak emission “is proportional to” 1/temperature
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↑ temperature = bluer the radiation
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λmax = 0.29cm/T
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λmax = max wavelength intensity; T = temperature in K;
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Stefan’s Law: Total energy radiated per second “is proportional to” temperature4
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↑ temperature = ↑ energy emitted
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F = σT4
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Energy flux F = energy per unit area (in J); T = temperature in K
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Stefan-Boltzmann constant σ: 5.67x10-8 W/m2·K4
SECTION 2.5 SPECTROSCOPY
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Spectroscope: instrument used to analyze radiation
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consists of an opaque barrier with a slit in it (to form a narrow beam of light), a prism (to split the beam into its component
colors), and either a detector or a screen (to allow the user to view the resulting spectrum)
Emission lines: “slices” of a continuous spectrum
o Continuous spectra: emits radiation of all wavelengths
o Each element has a signature emission spectrum
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Cannot alter color (frequency and wavelength) but can alter intensity
Absorption lines: gaps in a spectrum
o Shows where wavelengths of light have been absorbed by gases present
o Fraunhofer lines: solar spectrum absorption lines
Spectroscopy: study of ways in which matter emits and absorbs radiation
o Kirchoff’s laws:
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1) a luminous solid of liquid, or a dense gas, emits light of all wavelengths and produces a continuous spectrum
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2) a low-density hot gas emits light whose spectrum consists of bright emission lines
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3) a low density cool gas absorbs wavelengths from a continuous spectrum, leaving absorption lines in their place
SECTION 2.6 THE FORMATION OF SPECTRAL LINES
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Amount of light energy absorbed or emitted must correspond to the energy difference between two orbitals
o Photon energy “is proportional to” radiation frequency
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Connects energy of a photon to the color of light it represents
Atomic excitation
o atom absorbs a photon of radiation and transitions from ground state to first excited state, then emits photon of same energy
and drops back to ground state
o atom absorbs more energetic (higher frequency, shorter wavelength) photon, causing jump to second excited state
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1) can proceed directly back to ground state, emitting photon identical to the one that was absorbed
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2) can cascade down one orbital at a time, emitting two photons: one having energy equal to the difference between
the second and first excited states, and the other having an energy equal to the difference between the first excited
state and ground state
o More energetic photon = more photons released from higher excited state
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Balmer lines: “hydrogen series” observable part of hydrogen spectrum σ: 5.67x10-8 W/m2·K4
SECTION 2.7 THE DOPPLER EFFECT
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Object moving towards you: because source moves between the times of emission of one wave crest and the next, wave crests
in the direction of motion of the source are seen to be closer together than normal, while crests behind are more widely spaced
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Observer in front measures shorter wavelength, one behind sees longer
↑ relative speed of source and observer, ↑ observed shift
Recession: (apparent wavelength)/(true wavelength) = (true frequency)/(apparent frequency) = 1 + (recession velocity)/(wave
speed)
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Positive recession: source and the observer are moving apart
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Negative recession: source and the observer are approaching each other
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Blueshifted: wave measured by observer in front of a moving source (coming towards)
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Redshifted: wave measured by observer behind a moving source (going away)
SECTION 2.8 SPECTRAL-LINE ANALYSIS
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1) composition determined by matching spectral lines with known spectra of atoms and molecules
2) temperature of an object emitting a continuous spectrum can be measured by matching overall radiation with a blackbody
curve & detailed studies of spectral lines
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3) (line-of-sight) velocity measured by determining Doppler shift of spectral lines
4) rotation rate determined by measuring the broadening (smearing out over a range of wavelengths) by Doppler effect in
emitted or reflected spectral lines
5) pressure of the gas in emitting region determined by tendency to broaden spectral lines; greater pressure = broader line
6) magnetic field can be inferred from Zeeman effect (characteristic splitting it produces in spectral lines, when a single line
divides into two)
CHAPTER 3 Telescopes
SECTION 3.1 OPTICAL TELESCOPES
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Telescope: “light bucket” whose primary function is to capture as much radiation as possible from a given region of the sky and
concentrate it into a focused beam for analysis
o Reflecting telescope: use curved mirror to gather and concentrate beam of light
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Primary mirror: all light rays arrive parallel to its axis and are reflected back to a single point (focus)
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Focal length: distance between mirror and focus (primary focus)
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Radiation from a star enters the instrument, passes down the main tube, strikes the primary mirror, is reflected back
toward prime focus neat top, second primary mirror redirects light to more convenient location
o Refracting telescope: uses a lens instead of a mirror to focus light, relying on refraction rather than reflection
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Refraction: bending of a beam of light as it passes from one transparent medium into another
o Prefer reflecting instruments over refractors
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Chromatic aberration: lens in a refracting telescope focuses red and blue differently; requires high-quality glass
whereas mirrors don’t have this problem
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Glass lens blocks most of radiation for infrared and ultraviolet observations
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Large lens is heavy and difficult to support
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Lens has two surfaces that must be maintained, mirror only one
o Newtonian telescope: light is intercepted by flat secondary mirror before reaches prime focus and deflected 90° to an eyepiece
at the side
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Popular design for smaller telescopes
o Cassegrain telescope: light reflected by primary mirror towards the prime focus is intercepted by a convex secondary mirror,
which reflects the light back down the tube and through a small hole at the center of the primary mirror
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Hubble Space Telescope
Charged-coupled devices (CCDs): electronic detectors to create images
o When light strikes a pixel, charge builds up on the device; the amount of charge is directly proportional to the number of
photons striking each pixel (intensity) charge build up is measured electronically and image is obtained
o Advantages over photographic plates
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Efficiency: 75% of photons vs. <5% for photographic methods
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CCDs can take images 10-20x fainter
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CCDs produce a representation of an image in a digital format that can be placed directly to a computer
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Can compensate for known defects and background noise
Mauna Kea Obervatory, Hawaii: world’s highest ground-based observatory
o Twin Keck telescopes: largest ground-based telescopes
SECTION 3.2 TELESCOPE SIZE
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Light gathering power
o Exposure time: observe certain area for long period of time to collect more light
o Collecting area: area capable of intercepting and focusing radiation
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Intensity “is proportional to” diameter2
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↑ Observed brightness = ↑ area of telescope’s mirror
Resolving power
o Angular resolution: ability to form distinct, separate images of objects close together in a field of view
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Diffraction: tendency of light to bend around corners
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When a parallel beam of light enters a telescope, the rays spread out slightly, making it impossible to focus
the beam to a sharp point
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Degree of fuzziness determines the angular resolution
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Angular resolution (arc seconds) = [0.25*wavelength (µm)]/[telescope diameter (m)]
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o 1 µm (micrometer) = 10-6 m = 1000 nm
Diffraction-limited resolution: ↑ Telescope size = ↑ blurring effects of diffraction
SECTION 3.3 HIGH-RESOLUTION ASTRONOMY
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Turbulence: small winds in atmosphere make light from start refract slightly repeatedly
o Seeing: effects of atmosphere turbulence
o Seeing disk: circle over which a star’s light is spread
o Avoided by creating high ground-telescopes or above atmosphere space telescopes
Active optics: collection of techniques to control environmental and mechanical fluctuations in the properties of telescopes (control
mirror based on temperature & orientation)
o improve dome design to control airflow
o precise control of the mirror temperature
o use of actuators (pistons) behind the mirror to maintain its precise shape
adaptive optics: deforms shape of a mirror’s surface under computer control while image is being exposed in order to undo effects of
turbulence (corrects for atmospheric turbulence)
SECTION 3.4 RADIO ASTRONOMY
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radio telescopes: radio radiation telescopes
o Arecibo Observatory is largest, National Astronomy and lonospheric center
o Benefits
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Can observe 24 hours, regardless of weather
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Radio waves unaffected by matter in the way
Interferometry: two or more radio telescopes used at same time to observe same object
o Analyzes how the signals interfere with each other when added
o ↑ Baseline (distance separating telescopes) = ↑ resolution
SECTION 3.5 OTHER ASTRONOMIES
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Infrared telescope: sensitive to longer-wavelength radiation
Ultraviolet telescope: capture and analyze high frequency radiation
High-energy telescopes: x-rays and gamma rays
o Must be captured high above Earth’s atmosphere because none of it reaches ground
o Detection requires use of equipment different from that used to capture low energy
o X-ray observation: Passed through or absorbed through materials
o Gamma ray observation: count photons, but no real method
RADIATION
Radio
Infrared
Visible
Ultra violet
GENERAL CONSIDERATIONS
 Can penetrate dusty regions of
interstellar space
 Earth’s atmosphere largely
transparent to radio wavelengths
 Can be detected in daytime as well as
night
 High resolution at long wavelengths
requires very large telescopes
 Can penetrate dusty regions of
interstellar space
 Earth’s atmosphere only partially
transparent to IR radiation, so some
observations must be made from
space
 Earth’s atmosphere transparent to
visible light
 Earth’s atmosphere opaque to UV
radiation, so observations must be
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COMMON APPLICATIONS
Radar studies of planets
Planetary magnetic fields
Interstellar gas clouds
Center of Milky Way Galaxy
Galactic structure
Active galaxies
Cosmic background radiation
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Star formation
Cool stars
Center of Milky Way Galaxy
Active galaxies
Large-scale structure of the universe
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Planets
Stars and stellar evolution
Galactic structure
Large-scale structure of the universe
Interstellar medium
Hot stars
X-ray
Gamma-ray
made from space
 Earth’s atmosphere opaque to Xrays, so observations must be made
from space
 Special mirror configurations needed
to form images
 Earth’s atmosphere opaque to
gamma rays, so observations must
be made from space
 Cannot form images
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Stellar atmospheres
Neutron stars and black holes
Active galactic nuclei
Hot gas in galaxy clusters
 Neutron stars
 Active galactic nuclei
CHAPTER 4 The Solar System
SECTION 4.1 AN INVENTORY OF THE SOLAR SYSTEM
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Mostly flat, except Mercury at 7° angle
Density: mass/volume
Terrestrial planets: four innermost planets (Mercury, Venus, Earth, Mars)
Jovian planets: larger outer planets (Jupiter, Saturn, Uranus, Neptune)
TERRESTRIAL
Close to the sun
Closely spaced orbits
Small masses
Small radii
Predominately rocky
Solid surface
High density
Slower rotation
Weak magnetic fields
No rings
Few moons
JOVIAN
Far from the sun
Widely spaced orbits
Large masses
Large radii
Predominately gaseous
No solid surface
Low density
Faster rotation
Strong magnetic fields
Many rings
Many moons
SECTION 4.2 INTERPLANETARY MATTER
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Cosmic debris
o Asteroids
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Properties
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Anything larger than 100m in diameter
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Too small to be resolved by earth-based telescopes
o Can be sized by measuring the amount of sunlight they reflect
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Gravitational effect of an asteroid on its neighbors is very small
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Minor planets
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Carbonaceous asteroids: darkest asteroids with significant amounts of water ice and volatile substances and rich in
organic molecules; mostly outer part of belt
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Silicate asteroids: reflective of rocky material; mostly inner part of belt
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Asteroid belt: 2.1-3.3 AU from the sun, between Mars and Jupiter
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Revolve around sun in prograde orbits in same direction as planets
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Trojan asteroids: share orbit with Jupiter
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Earth-crossing asteroids: orbits intersect the orbit of Earth
o Comets
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Predominantly icy rather than rocky and have diameter 1-10km
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Nucleus: main solid body of an asteroid
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Dust particles and small rocky fragments, trapped within a loosely packed mixture of methane, ammonia,
carbon dioxide, ice, with 100 kg/m3 density
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Tail: comet’s brightness extends to form tail; always away from the sun
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Ion tail: straight, often made of glowing, linear streamers; indicates numerous ionized atoms
o
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Dust tail: broad, diffuse, gently curved; microscopic dust particles
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Coma: icy surface becomes too warm and forms dust an evaporated gas around the nucleus
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Hydrogen envelope: engulfs coma
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Kuiper belt: region in outer solar system similar to the asteroid belt but for comets
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Oort cloud: huge cloud of comets lying far beyond the orbit of Pluto, completely surrounding the sun
Meteoroids
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Anything smaller than an asteroid
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Meteorite: interplanetary debris that passes through atmosphere
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Micrometeoroids: in meteoroid swarm that cluster together that follow comets
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Radiant: Meteor shows are named after the constellation from whose direction they appear to come
SECTION 4.3 THE FORMATION OF THE SOLAR SYSTEM
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Formed approximately 4.6 billion years ago
Extrasolar planets: planets orbiting stars other than the Sun
Theory of the origin and architecture of our planetary system
o 1) each planet is relatively isolated in space
o 2) The orbits of the planets are nearly circular
o 3) The orbits of the planets all lie in nearly the same plane
o 4) The direction in which the planets orbit the sun (counterclockwise as viewed from above Earth’s North Pole) is the same as
the direction in which the Sun rotates on its axis
o 5) the direction in which most planets rotate on their axis is roughly the same as the direction in which the sun rotates on its
axis
o 6) the direction in which most of the known moons revolve around their parent planet is the same as the direction in which the
planet rotates on its axis
o 7) our planetary system is highly differentiated
o 8) asteroids re very old and exhibit a range of properties not characteristic of either the terrestrial or the jovian planets or their
moons
o 9) The Kuiper belt is a collection of asteroid-sized icy bodies orbiting beyond Neptune
o 10) the Oort cloud comets are primitive, icy fragments that do not orbit in the plane of the ecliptic and reside primarily at large
distances from the Sun
Nebula: large cloud of interstellar dust and gas; increate in rotation speed causes shape to change as it shrinks
o Nebular theory: idea that planets formed from a spinning disk (solar nebula)
Angular momentum “is proportional to” mass · rotation rate · radius2
o Energy is conserved at all times
Condensation nuclei: microscopic platforms to which other atoms can attach, forming larger and larger balls of matter
Condensation theory: Planet formation based on spinning disk
o Dust grains in the solar nebula formed condensation around the matter began to accumulate and form the first small clumps of
matter and sticking to other clumps
o Accretion: Surface areas of clumps increase and thus the rate at which they collect new material; gradual growth of objects by
collision
o Planetestimals: objects having gravitational fields just as strong enough to affect their neighbors
o Protoplanets/sun: accumulations of matter that would eventually evolve into the planets we know today
Formation of jovian planets
o Four largest protoplanets in outer solar system grew and became massive enough
o Giant planets formed through instabilities in outer cool regions of the solar nebula
SECTION 4.4 PLANETS BEYOND THE SOLAR SYSTEM
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Selection effect: plants far from parent star or lightweight don’t produce enough velocity fluctuations to be detectable
CHAPTER 5 The Solar System
SECTION 5.1 EARTH AND THE MOON IN BULK
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Surface gravity: strength of the gravitational force at the body’s surface
Escape speed: speed required to escape from the body’s gravitational pull
o Escape speed (km/s) = 11.2√[(mass of body in Earth masses)/(radius of body in Earth radii)]
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Structure of the Earth
o Inner core (solid and dense, 1300 km), outer core (molten, 3500 km), mantle (hard and rocky 3000 km)
o Hydrosphere: rivers, lakes, liquid oceans
o Atmosphere: air above the surface
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To determine whether retain atmosphere, compare escape speed with average speed of gas particles making up the
atmosphere
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Average molecular speed (in km/s) = 11.2√[(mass of body in Earth masses)/(radius of body in Earth radii)]
o Magnetosphere: greater altitudes where a zone of charged particles are trapped by planet’s magnetic field
SECTION 5.2 THE TIDES
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Tides: daily fluctuations in ocean level
o Direct result of gravitational influence of the Moon and Sun on Earth
o Tidal force: average gravitational interaction between two bodies determines their orbit around one another
Synchronous orbit: always has same side facing whatever it’s orbiting (i.e. the moon)
o Slightly slows Earth’s rotation, but only two milliseconds every century
SECTION 5.3 ATMOSPHERE
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The atmosphere
o Troposphere: everything below about 12 km
o Stratosphere: 40-50 km
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Ozone layer: solar ultraviolet radiation is absorbed by atmosphereic oxygen, ozone, and nitrogen
o Mesosphere: 50-80 km
o Ionosphere: above 80km, kept partially ionized by solar ultraviolet radiation
Atmosphere pressure decreases steadily with increasing altitude
Convection: constant upwelling of warm air and concurrent downward floor of cooler air to take its place
o At low altitudes, air immediately above the warmed surface is heated, expands a little, and becomes less dense, starts to rise
o at higher altitudes, air gradually cools, grows denser, sinks back to the ground, rushes to replace hot air that has risen
greenhouse effect: most of sun’s energy emitted in visible & near-infrared, so most of solar radiation not absorbed by or reflected from
clouds in the upper atmosphere shines directly onto Earth’s surface, thus heating it up
o carbon dioxide and water vapor absorb the infrared energy and only some of it escapes back into space, thus rest is radiated
back to surface and temperature rises
SECTION 5.4 INTERIORS
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seismology
o earthquake: sudden dislocation of rocky material near Earth’s surface
o seismic waves: move outward from the site of the quake
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primary waves (P-waves): pressure waves, like sound waves in air, that alternately expand and compress the medium
through which they move (side to side)
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travel through liquid & solids
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secondary waves (s-waves): shear waves which cause side to side motion (up and down)
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can’t travel through liquid
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density of matter in the interior can be inferred by measuring the time taken for waves to move from one site of an
earthquake to surface
differentiation: variation in density and composition in mantle
radioactivity: release of energy by certain unstable elements (uranium, thorium)
o rocky mantle is a poor conductor of heat, so heat builds up in interior
crust of moon is much thicker due to Earth’s gravitational pull
SECTION 5.5 SURFACE ACTIVITY ON EARTH
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continental drift
o plate tectonics: study of plate movement; continents are “passengers riding atop much larger plates”
o caused by convection in the upper mantle
o Pangaea: supercontinent many years ago when all continents were together
o no evidence of this on the moon
SECTION 5.6 THE SURFACE OF THE MOON
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maria: dark areas on moon’s surface; remnants of seas of molten lava
highlands: light areas on moon’s surface; higher areas
lunar erosion: from many collisions with meteoroids of all sizes which create craters
SECTION 5.7 MAGNETOSPHERES
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Magnetic field lines from the north and south magnetic poles
o Rapid rotation and conducting liquid core are needed for this
Van Allen belts: two zones of high-energy charged particles
o Magnetic field exerts a force on a moving charged particle, causing the particle to spiral around the magnetic field lines
o Electrons and protons from the solar wind become trapped by Earth’s magnetism
Aurora: particles escape from magnetosphere near north and south poles and collide with air molecules (aurora borealis/australis;
Northern/Southern Lights)
SECTION 5.8 HISTORY OF THE EARTH-MOON SYSTEM
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Impact theory: glancing collision between Mars-sized object and molten Earth might have caused pits of splattered Earth could have
recombined into a stable orbit and form the Moon
Oldest rocks in lunar highlands is approximately 4.6 billion years old; earth roughly the same
Because of Earth’s gravitational pull, lunar crust is thicker on far side than on near side, so more volcanic activity on our side
Moon is geographically dead and has been dead for a long time