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•Project presentations today!
•Exam 3 is Tuesday May 3 @
4:00pm. Covers Chapter 8 & 9.
The Great Debate
Washington D.C. 1920
Heber Curtis: the spiral
nebulae are “island
universes” like the Milky Way.
Harlow Shapley: The
Milky Way is enormous
beyond imagination and
is the entire universe
Edwin Hubble uses the 100” on
Mount Wilson to measure Cepheid’s
in the Andromeda nebulae
Hubble’s discovery is
announced in 1925
The Andromeda “nebula” is
almost a million lightyears
away and is, therefore, an
island universe like the
Milky Way. His numbers are
off because he is using the
wrong calibration for the
Cepheid’s he is observing.
Working with Hubble, Walter
Baade finally figures out the
errors in distance
There are two types of stars. Type I stars are like the Sun
with high “metal” content. Type II are low metal content
and found in globular clusters and the galactic bulge
In the late 1800’s something
was amiss in physics
The precession of the
perihelion of Mercury
was not what it should
be according to
Newtonian gravity
Aspects of Maxwell’s electromagnetic
theory hinted at non-Euclidian space
and time.
Michelson & Morley
Michelson and Morley
attempted to measure the
Earth’s motion through
the luminiferous aether.
The aether was the
medium through which
light traveled. They kept
coming up with a null
result…no detectable
movement.
Albert Einstein came up with the
Special Theory of Relativity to
explain some of the problems
In his theory there is no
luminiferous aether, no
preferred reference frame. The
speed of light is the same in all
reference frames
It took another decade for
Einstein to come up with the
General Theory of Relativity
According to General Relativity (published in 1916),
massive objects warp spacetime and other masses
must move through that curved spacetime.
Early solutions to GR suggested
an expanding universe
Wilhelm De Sitter, Alexander Friedmann and
Georges Lemaitre did calculations using
general relativity that indicated the universe
should be expanding
By 1925 Vesto Slipher had
spectra for 45 galaxies
They had star-like character and Slipher could identify
absorption lines and thus get redshifts. They were large,
several hundred km/s to over 1000 km/s
Hubble gets Humason to
measure more redshifts
Hubble wants redshifts
on even more distant
galaxies. He stretches
his own work on
measuring distances to
get the distance to the
galaxies Milton
Humason is measuring.
In 1929 Hubble publishes his
distance-redshift results
From the plots, Hubble
determines an “age” for the
universe
1
Age 
H
The problem is it is too small. Early estimates are an age of only
1.95 Gyr. By this time geologist are saying the Earth is 2 to 4
Gyr old. For most of the 20th century the Hubble constant will
slowly creep down from 500 km/s/Mpc to around 75 km/s/Mpc.
Current best estimate is 73.8 km/s/Mpc
Chapter 9: Astronomy’s
Widening Horizons
The Californians dominate the
big telescopes with the Keck's
Completed in the early 1990’s, they are still among the
largest telescopes in the world (for now).
Consortiums and international
collaborations have broken the
California domination
Kitt Peak is operated by
AURA: the Association of
Universities for Research in
Astronomy
Other telescopes like
Gemini, CFH and Subaru
have taken up residence on
Mauna Kea
The southern hemisphere has
gotten into the game
Cerro Tololo
and Cerro
Paranal are
home to 8.2
meter class
telescopes
The Australians built the AngloAustralian Observatory in the
1970’s
Photographic plates have been
replaced with CCD’s
The LSST CCD will be a 3.2 Gpixel camera. The computers that
process the data will be capable of handling teraflops of data
The difference between
photographic plates and digital
On the left is one of Hubble’s images
of M31 taken with the 100” telescope.
On the right is an image taken by an
amateur with a 5.1” apo-refractor and
a Canon 5D digital camera
The Next Generation of
Telescopes
The GMT and ThirtyMeter Telescopes will be
enormous. The LSST,
while only 8.2-m, will add
the time domain
There are now two methods for
making BIG telescopes
Combine
8.2m mirrors
or
make 1-m
segments
and combine
lots of them
The 1-m segments
are made using
“traditional”
methods. The 8.2m
mirrors are spin-cast
The Steward Mirror Lab is
where all 8.2m mirrors are made
Space Telescopes
The HST has been up for 26 years. It is “only” a 2.4-m
telescope. The James Webb Telescope is slated for launch
in 2018. It will be a 6.5-m telescope.
Radio Astronomy pre-WWII
In the 1930’s Karl Jansky
detected a signal from the
direction of the center of the
Milky Way
Also in the 1930’s
Grote Reber did
scans of the sky in
radio wavelengths
After WWII radio astronomy
began to advance rapidly
The NRAO was established
in 1956 and radio telescopes
began sprouting in Green
Bank WV
By 1963 the Arecibo Radio
Telescope was built
Built in a natural hollow in the mountains of Puerto Rico
the dish is 300-m across
The Very Large Array (VLA) is
Socorro NM uses interferometry
Each of the
27 dishes is
25-m in
diameter
Radio telescopes were able to
penetrate the obscuring dust and show
the spiral structure of the Milky Way
Radio telescopes also began discovering
objects outside the Milky Way
Cygnus A was one of the first “radio loud”
galaxies but because the radio lobes were so far
from the galaxy, the two weren’t associated
together for some time
Radio astronomy also answered
the “Big Question” in cosmology
Fred Hoyle was the leading proponent of the Steady
State Theory. It proposed that new matter was being
created in intergalactic space to make new galaxies
as the older galaxies moved away
Arno Penzias and Robert
Wilson ended the debate
In 1963 the two had been
trying to calibrate a radio
horn for satellite
communication when
they discovered the
cosmic background
radiation. A group at
Princeton, headed by
Robert Dicke, was trying
to build a radio telescope
to look for the CBR at the
same time but were
scooped.
Beyond Radio and Visible
To “see” wavelengths other than visible and radio requires
telescopes above the Earth’s atmosphere and astronomy
benefited from the space race between the US and USSR
Early “telescopes” were put on
V-2 rockets
Equipment would be loaded where the warhead had been
and sent as high as possible
After Sputnik, space astronomy
literally took off
The Orbiting
Astronomical
Observatory was
launched in 1968
and lasted for 8
years.
Skylab carried several small
telescopes
Among the telescopes was a
small x-ray telescope that
was used to study the Sun
By the 1980’s a number of space
telescopes were launched
IRAS, an infrared
telescope, was
launched in 1983
COBE was launched in 1989
Planetary astronomy has
benefited the most
While they weren’t astronomers,
the Apollo astronauts learned a lot
The discovery of exotic objects
First came the discovery of starlike objects that were radio loud
In visible light they looked like a star but they were radio
loud and stars don’t produce radio waves so they were
called Quasi Stellar Radio Sources or Quasars
Maarten Schmidt measured the
spectra of a quasar and found
extreme redshift
Eventually a super massive
black hole theory is proposed
The jet from a central supermassive black hole creates
radio lobes when it plows into intergalactic gas. The
bright accretion disk around the black hole is only the
size of the solar system, thus the star-like appearance
The Hubble Space Telescope
was eventually able to resolve
host galaxies
In 1967 Jocelyn Bell, working
under Antony Hewish,
discovered pulsars
Pulsars are spinning neutron
stars
Light is emitted out the
magnetic axis via
synchrotron emission
Binary pulsars have proven
General Relativity under
extreme conditions
The first were
discovered by
Russell Hulse
and Joseph
Taylor in 1974.
The won the
Nobel Prize for it
in 1993
The Universe is a violent place
The discovery of Quasars was
one of the early hints of violence
The environment
around the event
horizon is one of the
most violent places in
the universe
Pulsars are also violent places
Eruptions from the
surface of
magnetars, extremely
magnetic neutron
stars, can lead to
flashes of gamma
rays and other high
energy radiation.
White dwarfs in binary systems
can produce nova and supernova
Red and Blue Supergiants
eventually go supernova
And then there are the small
scale things
The ultimate in violence was the
Big Bang
The gulf between
astronomers on the cutting
edge and ordinary people
In 1925, this is how most people living outside cities went.