Lecture 1 The Celestial Sphere Views of the Universe.
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Transcript of Lecture 1 The Celestial Sphere Views of the Universe.
Lecture 1 Lecture 1 The Celestial Sphere The Celestial Sphere Views of the UniverseViews of the Universe
The Celestial SphereHistory
The Greek traditionCopernican Revolution
Modern View of Universe The Universe at a glance
Positions on the celestial sphereAltitude-Azimuth coordinate system Equatorial coordinate systemDaily,Seasonal changes, Precession
Measurements of time
The Geocentric Universe
The Geocentric Universe• Celestial Spheres
– Stars attached on a sphere that rotates about an axis that passes through the north and south celestial poles…simple idea…
– “Wandering stars”, planets exhibit retrograde motion…complication!
– Epicycles on deferents….
Retrograde Motion
Copernican Revolution• Heliocentric - Sun centered
– Easily explains retrograde motion
But Copernicus still hung on to perfect circles … could not predict planetary positions better then Ptolemy
Bringing order to planets• Superior Planets• Inferior planets
– Greatest western (eastern) elongation (mercury 28 venus 47)
• Conjuction/Opposition• Synodic Period(S)
Time interval between oppositions
• Sidereal Period (P)Time interval to complete one orbit relative to
the background stars
(inferior)
(superior)
The Universe at a GlanceThe Universe at a GlanceA Modern View of the UniverseA Modern View of the Universe
Some simple observations of the universe… Some simple observations of the universe…
WhatWhat’’s out there?s out there?
How does one study Astrophysical objects?How does one study Astrophysical objects?
Some examples of what we understandSome examples of what we understandStellar AstrophysicsStellar AstrophysicsBig Bang CosmologyBig Bang Cosmology
Some examples of what we donSome examples of what we don’’t understandt understand
Observational AstronomyObservational Astronomy Fundamental ObservationsFundamental Observations
Sky is generally dark at night…Sky is generally dark at night… Really Bright object in the Sky during Really Bright object in the Sky during ““daytimedaytime””…… Sometimes there is a pretty bright object in the Sky at Sometimes there is a pretty bright object in the Sky at
night…night… Some bright pinpoints that remain relatively fixed..Some bright pinpoints that remain relatively fixed.. Some bright pinpoints that wander around…Some bright pinpoints that wander around… Some Some ““FuzzyFuzzy”” objects objects
Detailed ObservationsDetailed Observations DistanceDistance TemperatureTemperature SpectraSpectra ……..
What do these observations tell us What do these observations tell us about the Universe?about the Universe?
The Universe at ~300K years
Full Sky Map of Microwave intesity from COBE satellite
WMAP Temperature fluctuations
Scientific MethodScientific MethodLearning about the UniverseLearning about the Universe
Observe Observe MeasureMeasureCatalogCatalogLook for orderLook for orderFormulate TheoryFormulate TheoryModel PhenomenonModel PhenomenonLearn Something about the Learn Something about the
UniverseUniverse
Check Theory byComparing Model with observations
Napoleon’s Gravitational Theory
My Gravitational Field Equation’s Predictthat the Universe has existed forever, is infinitely
large and uniformly filled with stars with an averageSpacing of l light year
Checking Napoleon’s Gravitational Theory
Napoleon what would the night sky look like
if your theory is right?
Napoleon’s Night Sky
Checking Napoleon’s Gravitational Theory
The night sky is basically dark and you, my friend, are dead wrong..
Einstein’s Gravitational theory is better than Newton’s
Qso0957+561
Hubble ImageNewton’s theory: gravity does not deflect light
Einstein’s theory: space-time is warped … light will be deflected
Another Simple ObservationAnother Simple ObservationLocation of planetsLocation of planets
Planets lie along ecliptic plane
Mercury never further than about 28 degrees from sun. Venus never further than about 48 degrees from sun
Mars, Jupiter, Saturn,…not constrained to lie close to sun
Retrograde Motion
…
What do these observations tell you????
Heliocentric Solar System
• Pluto kinda looks out of place even on this diagram….
Astrophysical ObjectsAstrophysical Objects
The Sun
The Moon
Planets and Moons
Study solar phenomenasuch as flares, sun spots
Lunar “Cartography”
Study orbits of planetsand their moons
Astrophysical ObjectsAstrophysical Objects
Comets
Asteroids
Stars
Track asteroids beforethey “strike”….
Search for and track comets
Measure orbital periods of binary and Trinary systemsVariable Stars….
Astrophysical ObjectsAstrophysical Objects
Planetary Nebulae
Globular Clusters
Observe remnants of oldsupernovae
Determine age of starsin globular clusters
Astrophysical ObjectsAstrophysical Objects
Galaxies
Diffuse Nebulae
Introduction to Introduction to Astronomy/AstrophysicsAstronomy/Astrophysics
Astrophysical Objects ( Things in the Universe)Astrophysical Objects ( Things in the Universe)Planets and Moons….Sun and StarsGalaxiesExotic objects
AGNs, BlazarsGRBsQuasars
Dark Matter ???Dark Energy???
How do we study them?
Light as a MessengerLight as a MessengerAnalyzing StarlightAnalyzing Starlight
SpectroscopySpectroscopy
Basic PhysicsBasic PhysicsBlackbody RadiationBlackbody RadiationColor Color Temperature Temperature
Classification of Stars using Spectral Type
and Brightness
Hertzsprung Russel Hertzsprung Russel DiagramDiagram
The evolution of a star from birth to death traces out a path on the H-R diagram…
Stellar Evolution
Stellar Evolution in a Stellar Evolution in a nutshellnutshell
Death of StarsDeath of Stars•White DwarfWhite Dwarf
•Electron degeneracy pressureElectron degeneracy pressure•M<1.4 MsunM<1.4 Msun
•Neutron StarNeutron Star•Neutron Degeneracy PressureNeutron Degeneracy Pressure•1.4Msun < M <2.8 Msun1.4Msun < M <2.8 Msun
•Black HoleBlack Hole•M>2.8 MsunM>2.8 Msun
•““SmithereensSmithereens””
Supernova remnantsSupernova remnants
GalaxiesGalaxies
• What are they?• Where are they?• How are they moving?• What does this tell us?
(Gary Walker)
Galactic RedshiftsGalactic RedshiftsTell us something?Tell us something?
How do we know that the How do we know that the Universe is expanding?Universe is expanding?
Cosmological Distance ScalesCosmological Distance Scales
• Bootstrap method– The astronomical unit – radar and kepler– Trigonometric Parallax– Spectroscopic Parallax– Cepheid-variables– Galaxy Standard Candles– Galaxy Luminosities
Cosmological Distance Scales Cosmological Distance Scales
Trigonometric ParallaxTrigonometric Parallax
•Parsec=3.26 light year~9.5 trillion km (Distance at which 1AU subtends 1 arcsec)
Cosmological Distance Scales Cosmological Distance Scales
Galaxy Standard CandleGalaxy Standard CandleType IA SupernovaeType IA Supernovae
•Explosion of white dwarf in a binary system
•Equivalent to a 1028 Megaton explosion Standard Candle
•Determine distance from apparent luminosity and inverse square law
Recession velocity v DistanceRecession velocity v DistanceHubble ConstantHubble Constant
H = 72+/-8 km/sec/Mpc from HST analysis (2000)
Universe is Universe is ExpandingExpanding
Accelerating UniverseAccelerating UniverseType IA SupernovaType IA Supernova
as standard candlesas standard candles
Indication that expansion of universe is accelerating fromobservation of apparent distance to galaxy at a given redshift not being consistent with the expectation from a universe undergoing constant expansion.
For more info…http://www.lbl.gov/supernovasnvideo.htmlsaul_sm.qt
DARK ENERGY
Some Examples of what we donSome Examples of what we don’’t t
understandunderstand Gamma Ray burstsGamma Ray bursts
Gamma Ray BurstsGamma Ray Bursts Possible Cause
Possible EffectsFearful Dinosaurs?UHECRs???