Brief history Astronomy PART II from Hershel  to accelerating Universe


PART I click here (from Copernicus to Newton)

movie to watch: greatest discoveries in Astronomy from discovery channel (42 minutes)

Willam Herschel

He gave up music for astronomy. Built huge telescopes and discovered Uranus and the milky way.
+ other objects like comets.
Here to learn more

general relativity

At the end of 19th century some problems with Newtonian Physics arose.
Comes quantum mechanics and general relativity.
General relativity is an extension of Newton's theory of relativity for large masses.
For example, Newtonian Physics could not account for the motion of Mercury.
Newton's Physics explains gravity by an invisible force pulling instantaneously on masses,
taking grab on them. The Sun pulls on the EArth and forces the EArth into Orbit.
Einstein says gravity does not act instantaneously. Gravity travels at the speed of light.
So if the Sun was to disappear it would take 8 minutes for the EArth to move in a straight line (gravity is no more).
Also, Einstein explained how the curvature of space and time accounts for gravity. The Sun curved the space around it
and the Earth moves in one fold of the fabric of space. The space pushes on Earth and prevents it to escape :
The space-time is like a trampolie, the Sun like a bowling Bowl and the EArth a marble stuck in a curve.

watch that movie (from NOVA)

Einstein's theory triumphed when the light from a star was observed to be curved during a solar eclipse.
lNo matter ca go faster than the speed of light and the speed of light does not depend on the
frame of reference it is measured in ! unlike time/energy/length
Einstein's big ideas :
- The speed the light does not depend on the frame of reference it is measured in ! (see below)
- E = mc2    Energy and mass are interchangeable.  As you increase the speed , you increase the energy
and therefore the mass (inertia). Mass becomes infinite at he speed of light.
- length, time , momentum , energy depends on the frame of reference you are measuring in


llight is made of particle waves = photons. Each photon is a bundle of energy.
photons have no mass. But they have energy proportional to their frequency.
Einstein + Max Plank = Quantum mechanics. photo electric effect shoewd that Einstein was right.
photons= bunch of bundles of energy

galaxies, universe is expanding , big bang

1927 Edwin Hubble using the observatory at Mt Wilson understands that some of these
fuzzy clouds observed in the background of stars are in fact far away galaxies.
With the new telescopes scientists could have a better look at the sky.
White nebulae were spotted but could not be explained.
Edwin Hubble understand these nebulae are in fact galaxies.

By looking at the redshift of galaxies he theorized that the Universe is expanding at a constant rate.

Using the Cepheid stars (variable stars) Hubble   computes the distance to these galaxies and their receding speed.
Farther are the galaxies, faster is their relative speed. The Universe is expanding. So it was smaller in the past/
but how small ?
watch the movie George Gamow and the big bang
George Gamow comes with the theory of the big bang. The Universe startes with an epxlosion that created
not only hydrogen and helium but also space and time.

The theory of the Big Bang is developed by Georges Gamow and others.
He described the very early Universe are being a " ylem" which means soup in yiddish.

his team from Princeton university predicts the Cosmic  Microwave Background Radiation.

radio waves from the center of the milky way are detected

Jansky from the Bell laboratory detects radio waves coming from the center of the Milky Way .
(he was studying the halo of gas in the center the galaxy)
in the constellation of the sagittarius. Later, a super massive black hole was identified to be the source
of the radio waves. Radio astronomy was born.

NOTE: Since the late 1970s, astronomers have kept watch on an object at the Milky Way's core known as Sagittarius A-star.
When viewed through a radio telescope, Sagittarius A-star appears so bright that many believe only a black hole's gravity could fuel it

Most of that light scatters into the interstellar dust that lies between us and the Milky Way's core,
but radio waves and x-rays can penetrate the shroud of dust to reach the earth.
watch the movie about radio astronomy

dark matter

Dark matter was postulated by Fritz Zwicky in 1934, to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters.
Subsequently, other observations have indicated the presence of dark matter in the universe, including the 
rotational speeds of galaxies,gravitational lensing
of background objects by galaxy clusters such as the 
Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.
note: Zwicky also understood how neutron stars worked. He is famous for calling his colleagues " spherical bastards "
dark matter = the speeds of galaxies are larger than expected.

Fritz Zwicky

dark matter in 3D

watch movie dark matter
here another evidence for dark matter: the Bullet Cluster

without sound
gravitationnal lensing

.(using the method gravitational lensing)

cosmic microwave background radiation

watch the movie: evidence for the big bang from discovery channel
radiation from 300,000 years after the Big Bang was detected . The signal is in
 the micro wave range because it was stretched while the universe was expanding.
In 1965,Arno Penzias and Robert Woodrow Wilson at the Crawford Hill location of Bell Telephone Laboratories
 in nearby Holmdel Township, New Jersey had built a Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments.
They detect the signal but don't know what it is.
They contacted George Gamow from the University of Princeton (and team) who predicted this signal to be the left over of the Big Bang
and was about to build a device to detect it. Wilson and Penzias got the Nobel Prize but unfortunately they didn't share it with
Gamow and coe who predicted it and explained it. there is a funny story about the couple of pigeons who were nesting in the antenna.
Wilson and Penzias thought the drops from the pigeons were the cause of the microwave signal. So they killed the pigeons.
that didn't stop the signal.
Later a satellite and a probe (cobe, WMAP) were sent to get a better record of the signal and we have refined image of the
early Universe with the seeds of the galaxies.
WATCH MOVIE ABOUT cosmic microwave background

form WMAP

Gamma rays burst
69 to 71 /  1 burst per day
During the Cold war American were " listening" to Gamma rays that could have came from
soviet union nuclear tests.  (see movie Dr.strangelove with Peter Sellers)
They recorded Gamma burst but coming from space.
Gamma rays burst are still not well understood. The long ones come probably from exploding supernovae
very far away (in time). The short ones are more mysterious. They maybe due to colliding neutron stars? (move to 4:50 to skip the tech)

pulsars? see animation
gamma rays are also spew out by supermassive black holes.
 short video
swift is a space craft that studies the BRBs with 3 instruments. 1 detect the GRB and the others collect the after glow
in X rays and UV/visible.
More here

Gamma rays burst may be connected to mass extinction on EArth


exoplanets are found. WE can't detect Earth like planets yet but we can detect Jupiter's like planet/
Extrasolar planets were first confirmed to be orbiting the pulsars PSR B1257+12 and PSR B1620-26.
Aleksander Wolszczan was the first one to find 2 exoplanets around a pulsar in 1992.

These discoveries were announced in 1992 and 1993 respectively. The first extrasolar planet to be found orbiting a main sequence star,
51 Pegasi b, was discovered in 1995.
100s of exoplanets have been found.  Geoff Marcy from Berkeley University has found many of them/
He found a 5 planets system in the constellation of cancer.
This is the largest number of exoplanets found around 1 star.
including a planet taking 2.8 days to go around.
see here for more about the 5 planets solar system
Aleksander Wolszczan was the first one to find 2 exoplanets around a pulsar in 1992.

There are different ways to detect an exoplanet/ The method the most used is by detecting the wobble of the star due to the motion of the planet.
The planet pulls on the star a little and the induced motion of the star can be detected by " looking " at the blueshift/redshift of the star.
It works best if the orbit of the star is edge on. Another method is the transit one. When the planet travels in fromt of the star, the light of the star is
dimmer. The brightness is recorded. Other methods are used too.

First photo of an exo planet

Kepler telescope launched in 2009 is looking for more planets in our milky way specially planets
the size of Earth. It looks at the dimmer light of stars as planets travels in front.
the dimming of the star due to the planet. more on Kepler   Kepler webisite. All the planets discovered so far. 5?
SEARCH FOR PLANETS in your spare time

UPDATE: 7 planets
/ 100 light years away. 500 so far altogether.

accelerating universe

2 teams in cAlifornia ,
 Supernova Cosmology Project at Lawrence Berkeley National Laboratory and  High-z Supernova Search Team
accelerating expansion of the universe. Among the Sicientists Saul Perlmutter and Alex Filippenko (best lecturer @ Berkeley)
It was done by observing the type IA supernovae. If the Universe is expanding, it is pulled a some kind of energy/force.
Since scientists don't know what it is, it is called dark energy. Einstein called that " anti gravity" the cosmological constant.
He thought he was wrong and called this constant the greatest blunder of his life.

watch dark energy movie

conclusion: cosmology 101