Lecture 1
The Celestial Sphere
Views of the Universe
The Celestial Sphere
History
The Greek tradition
Copernican Revolution
Modern View of Universe
The Universe at a glance
Positions on the celestial sphere
Altitude-Azimuth coordinate system
Equatorial coordinate system
Daily,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
ì1/P -1/Pearth
1/S = í
î1/Pearth -1/P
(inferior)
(superior)
The Universe at a Glance
A Modern View of the Universe
Some simple observations of the universe…
What’s out there?
How does one study Astrophysical objects?
Some examples of what we understand
Stellar Astrophysics
Big Bang Cosmology
Some examples of what we don’t understand
Observational Astronomy
 Fundamental Observations
 Sky is generally dark at night…
 Really Bright object in the Sky during “daytime”…
 Sometimes there is a pretty bright object in the Sky at
night…
 Some bright pinpoints that remain relatively fixed..
 Some bright pinpoints that wander around…
 Some “Fuzzy” objects
 Detailed Observations
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Distance
Temperature
Spectra
….
What do these observations tell us
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 Method
Learning about the Universe
Observe
Measure
Check Theory by
Catalog
Comparing Model
with observations
Look for order
Formulate Theory
Model Phenomenon
Learn Something about the
Universe
Napoleon’s Gravitational
Theory
My Gravitational Field Equation’s Predict
that the Universe has existed forever, is infinitely
large and uniformly filled with stars with an average
Spacing 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
Newton’s theory: gravity does not
deflect light
Einstein’s theory: space-time is
warped … light will be deflected
Hubble Image
Another Simple Observation
Location 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 Objects
è The Sun
Study solar phenomena
such as flares, sun spots
è The Moon
Lunar “Cartography”
è Planets and Moons
Study orbits of planets
and their moons
Astrophysical Objects
è Comets
Search for and track
comets
è Asteroids
Track asteroids before
they “strike”….
è Stars
Measure orbital
periods of binary
and Trinary systems
Variable Stars….
Astrophysical Objects
è Planetary Nebulae
Observe remnants of old
supernovae
è Globular Clusters
Determine age of stars
in globular clusters
Astrophysical Objects
è Galaxies
è Diffuse Nebulae
Introduction to
Astronomy/Astrophysics
Astrophysical Objects ( Things in the Universe)
Planets and Moons….
Sun and Stars
Galaxies
Exotic objects
AGNs, Blazars
GRBs
Quasars
Dark Matter ???
Dark Energy???
How do we study them?
Light as a Messenger
Analyzing Starlight
Spectroscopy
Basic Physics
Blackbody Radiation
Color  Temperature
Classification of Stars
using Spectral Type
and Brightness
Hertzsprung Russel
Diagram
The evolution of a star from
birth to death traces out a
path on the H-R diagram…
Stellar Evolution
Stellar Evolution in a
nutshell
Death of Stars
•White Dwarf
•Electron degeneracy pressure
•M<1.4 Msun
•Neutron Star
•Neutron Degeneracy Pressure
•1.4Msun < M <2.8 Msun
•Black Hole
•M>2.8 Msun
•“Smithereens”
Supernova remnants
Galaxies
(Gary Walker)
•
•
•
•
What are they?
Where are they?
How are they moving?
What does this tell us?
Galactic Redshifts
Tell us something?
How do we know that the
Universe is expanding?
Cosmological Distance Scales
• Bootstrap method
– The astronomical unit – radar and kepler
– Trigonometric Parallax
– Spectroscopic Parallax
– Cepheid-variables
– Galaxy Standard Candles
– Galaxy Luminosities
Cosmological Distance Scales
Trigonometric Parallax
•Parsec=3.26 light year~9.5 trillion km
(Distance at which 1AU subtends 1 arcsec)
Cosmological Distance Scales
Galaxy Standard Candle
Type 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 Distance
Hubble Constant
H = 72+/-8
km/sec/Mpc from
HST analysis
(2000)
Universe is
Expanding
Accelerating Universe
Type IA Supernova
as standard candles
Indication that expansion of
universe is accelerating from
observation 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/supernova
snvideo.html
saul_sm.qt
 DARK ENERGY
Some Examples of what we don’t
understand
Gamma Ray bursts
Gamma Ray Bursts
Possible Cause
Possible Effects
Fearful Dinosaurs?
UHECRs???