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

CMB Timeline

WMAP link

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???