Transcript Our Place in the Universe: Sizing up the Heavens

Our Place in the Universe:
Sizing up the Heavens
Reading: Marshak,
Ch. 1
Stellar Observations –
What can you see in the stars?
•Position and apparent changes in position through time
(I.E., motion)  mass (from orbital motions), distance.
•Brightness and apparent variations through time  size,
temperature, distance.
•Color (spectrum) and apparent variations through time
 composition, temperature, direction of motion and
velocity relative to observer.
•Apparent Size and shape and variations through time 
stars, galaxies, nebula (clouds of dust and gas), comets,
planets, etc.
Parallax – apparent shift in position of object
relative to background due to change in
perspective of viewer.
Stellar parallax allows distance to the stars
to be determined.
Parallax only measurable at distances <
several thousand light years.
*Stellar Brightness (“magnitude”) – depends
on distance and intrinsic brightness due to
size and temperature.
* By identifying class of star, can estimate
absolute magnitude and solve for distance.
Taking the Temperature of a Star
* Spectrum – the distribution of wavelengths (colors) of light.
* The hotter the body, the more energy emitted and the shorter the
wavelengths (violet, ultraviolet, gamma rays, x-rays)
Same ideas apply on Earth:
Ozone Composition
(O3) in upper
atmosphere absorbs UV
•As light passes
light, protecting surface;
through
theEarth,
outer
sunlight
strikes
gases to
ofheat,
the and
star,
converts
radiates
as long
wl infrared
certain
wavelengths
radiation
(heat); infrared is
are absorbed
absorbed by CO2 and other
“fingerprinting” its
“greenhouse gases” in
composition.
atmosphere,
thus retaining
heat.
Do you know this sound?
What is it? How does it change?
The Doppler Effect
Approaching sound source compresses sound
waves, shortening wavelength and increasing
pitch.
Receding sound source stretches wavelengths
and lowering pitch.
Red Shift
The Doppler Effect applied to light – Spectrum of
approaching stars is shifted to shorter wave-length
(blue shift) whereas receding stars experience red shift.
The faster the relative motion, the greater the shift.
Amazingly, almost all stars in the Universe are red
shifted.
Amazingly, the Greater the Distance,
the Greater the Red-Shift
Our Deepest View into Space and Time
Expanding Universe
First recognized by Edwin Hubble in 1920’s.
Projected backward, the expanding universe
implies that ~12-15 billion years ago all the
matter of the universe exploded outward from
a single point – “The Big Bang”
Stellar Evolution – Variations with Mass
White dwarfs – “degenerate
matter”: a teaspoonful
weighs several tons
Neutron Stars – protons and
electrons forced together to
form neutrons – a pea-sized
piece would weigh
100,000,000 tons
Black Holes – so massive
and dense not even light can
escape its gravitational pull.
Star Birth in
Eagle Nebula
Birth of A Solar System –
Protoplanetary Dust Rings
Prelude to Star Death
Relicts of a Supernova, 1054 A.D.
How to “see” a Black Hole