Stars and Galaxies Intro 01/07/2014
AST201 – Stars and Galaxies
Lecture 1 – January 7, 14
Hubble photo “Hubble extreme deep field”
Matter is what produces gravity
Contents of the Universe
Fritz Zwicky – in 30s he studied clusters of galaxies and he figured out how large the galaxies were and
how they were moving around in space (in response to each others gravity) (depending on how big they
are, you can measure how fast they are moving) Most of the mass of galaxy clusters were invisible “missing
Vera Rubin – studied individual galaxies and how fast each one is spinning, “Kepler’s 3 law” the law of
gravity says the farther you are from the center of the galaxy, the slower you are orbiting. Rubin’s
observation was the opposite – the farther you are from the center, the faster you are orbiting. –compared
to Zwicky’s missing mass prediction
Up to 90% of the masses of these galaxies is invisible – no matter what telescope used
Rubin’s contents of the universe – 10% stars, galaxies, planets, gas, dust, etc. 90% dark matter
In 1998 it was discovered that 68.3% was dark energy, 26.8% dark matter, 4.9% ordinary matter (stars,
4.9% of the universe is “luminous” matter or “lightemitting matter”
97.5% of the universe is “missing”
Most of the universe is very empty Chapter 1 – Intro to Astronomy 01/07/2014
Reading Goals: Chapter 1 – Intro to Astronomy 01/07/2014
A very big mystery: the Dark Universe
Explain what the Hubble eXtremely Deep Field is, how it was produced, and what it tells us about the
overall makeup of the universe.
Describe the overall composition of the universe in terms of matter, energy, dark matter, and dark energy.
Identify one piece of evidence for the existence of dark matter.
Develop your willingness to ask “Why?” and “How do we know?”
Get comfortable discussing science and solving problems with your peers
Get to know at least one other person in the class
A very big mystery: the Dark Universe
explain what the Hubble eXtremely Deep Field is, how it was produced, and what it tells us about the
overall makeup of the universe
Describe the overall composition of the universe in terms of matter, energy, dark matter, and dark energy
Identify one piece of evidence for the existence of dark matter
A Modern View of the Universe
1.1 The Scale of the Universe
Our Cosmic Address
Universe> local group(galaxy cluster)> Milky Way galaxy> Sol(ar) System>Earth
Our solar system: located about 2/3 away from galactic center to edge of galactic disk.
Our milky way: among largest 40 galaxies in local group
Our local group: located in outskirts of local supercluster
Astronomical Distance Measurements
Astronomical Unit (AU): Earth's average distance from the Sun (about 150 million km, 8 light
minutes) describes distances within solar system
LightYear (ly): distance light travels in 1 year (about 10 trillion km, 63,000 AU) describes distances of
stars/galaxies Chapter 1 – Intro to Astronomy 01/07/2014
Looking Back in Time
Sirius: brightest star in sky 8 lightyears away. Because it takes the light 8 years to travel the distance, we
see Sirius as it was 8 years ago.
Orion Nebula: giant cloud in which stars/planets are forming 1500 lightyears away.
Andromeda Galaxy: 2.5 million lightyears away.
Alpha Centauri: nearest star system to ours; 4.4 lightyear
"The farther away we look in distance, the further back we look in time"
The Observable Universe
Universe estimated to be 14 billion years old; distance of 14 billion lightyears marks boundary (horizon) of
our observable universe.
Contains nearly 100 billion galaxies
1.2 The History of the Universe
The Big Bang, Expansion, and the Age of the Universe
The universe is expanding: the average distances between galaxies are increasing with time. Galaxies
and objects within them are not.
Stellar Lives and Galactic Recycling
Gravity drives collapse of clouds of gas/dust to form stars/planet compresses material in cloud to the point
at which center becomes dense + hot enough to generate energy by nuclear fusion
Star lives as long as it can shine with energy from fusion, dies when it exhausts usable fuel
In final death throes, star blows contents back into space. Most die in supernova
Blown contents become parts of new clouds and form new stars Chapter 1 – Intro to Astronomy 01/07/2014
Universe contained only hydrogen, helium and a trace of lithium. Other elements were manufactured by
stars through nuclear fusion + reactions accompanying explosions
The History of the Universe
The Big Bang The Milky Way Forms Earth forms Early life on Earth Cambrian explosion Rise of
the dinosaurs Extinction of the dinosaurs Early hominids evolve Modern humans evolve Agriculture
arises Pyramids built Kepler and Galileo show that Earth orbits the Sun Now
(Earlier histories occurred farther apart in time, last few happened very quickly in cosmic time)
1.3 Spaceship Earth
How is Earth moving through space?
Rotation and Orbit
Rotation daily, west to east counterclockwise when viewed from North Pole (Sun rises in E, sets in W),
Orbit yearly, 100,000 km/hr, axis tilt is 23.5 pointing at Polaris/North star, also counterclockwise
(consequence of birth)
Motion Within the Local Solar Neighbourhood
Stars move randomly rela