Astronomers, Theories, and

Galaxies!

Whirlpool Galaxy, M51

Sketch: 1845 (ground telescope)

Whirlpool Galaxy, M51

Hubble Telescope: 2001

History of Astronomy

• Ancient Greek philosopher named Aristotle

• wrote about several scientific ideas

• His ideas were accepted by Western Civilization

• Believed the Universe was “Earth-centered” or “Geocentric”

The “Geocentric” Model

• Earth Centered

• States that everything in the universe orbited around Earth

• Supporters : Aristotle, Ptolemy, the catholic church

Ptolemy (150 AD)

• Roman citizen that lived in Egypt • Worked as an astronomer and a mathematician• Used mathematics to develop models of the structure of the Universe• His model was also Earth centered or “Geocentric”

Nicolaus Copernicus (February 19, 1473 – May 24, 1543)

Religious man who was also an astronomer

First astronomer to formulate a Heliocentric model

“Heliocentric” model places the Sun as the center of the Universe. Collected data when he made

observations of the sky

1.Earth moved with a daily motion on its axis

2. Also moved with a yearly motion around a stationary sun.

Heliocentric (Greek)

Helios = Sun Centric= Center

Copernicus’ Discoveries

The Heliocentric Model

• Sun centered

• Supporters: Copernicus, Galileo, Newton

Ptolemy’s Universe

Copernicus’ Universe

Galileo Galilei Made improvements to the telescope which led to better observations

• Beginning in 1610, Galileo began making observations of Venus and its phases.

• The observations gave further evidence to support the heliocentric model by Copernicus. (100 yrs later)

Ptolemy’s ModelGalileo’s Model

Inner Planet Comparison (w/ Pluto – the former planet!)

Outer and Inner Planets

Our Star!

What goes up, must come down

• The origin of the Big Bang theory can be credited to Edwin Hubble. Hubble made the observation that the universe is continuously expanding.

Therefore, if the universe is expanding… going back in time suggests that all matter came from one source!

1. The universe may have began billionsof years ago with a big explosion.

THE BIG BANG THEORY

2. The explosion of the big bang sent all matter moving apart.

3. Within fractions of a second, the universe grew from the size of a pin to 2000 times

the size of the sun.

4. After the explosion the universe would have been a dense swirling mass of elementary particles……

As matter cooled, hydrogen and helium gas formed.

5. Matter began collecting in clumps and eventually formed into protostars.

6. Over one billion years after the initial explosion, the first stars would have been born.

According to the Big Bang model, the universe expanded from an extremely dense, hot state and continues to expand today.

Oscillating Theory

• universe has gone through periods of expansion and contraction

• the universe is currently in a period of expansion!

• The oscillatory universe, originally derived by Alexander Friedman in 1922

• suggests that the universe undergoes a series of oscillations

• Each beginning with a big bang and ending with a big crunch.

• After the big bang, the universe expands for a while before the gravitational attraction of matter causes it to collapse back in

Steady State Theory• Scientists first thought the universe was static

and that its appearance has never changed.

• This is called the Steady State Theory• In this theory, galaxies are not moving away from

one another• New stars are being made from energy in the

center of galaxies

What will happen to the universe in the future?

• Open Universe Theory:The universe will keep expanding forever.

• Closed Universe or Big Crunch Theory:

Gravity will pull the universe back together again into one object and start the process over again.

What is the main piece of evidence that

supports the big bang theory?

Most of the stars and galaxies seen from Earth are showing a

red shift in the spectrum of light being given off.

Edwin Hubble

Hubble noticed redshifts in the light from the galaxies, and concluded that galaxies are moving away from each other. The

Universe is expanding! 1929

Galaxies…• Group of stars, dust, and gas held together by

gravity• There are over 100 billion galaxies in the

universe• We live in the Milky Way Galaxy

NGC 7331 is often referred to as "the Milky Way's twin."

• Galaxies can be found in large groups called clusters

Sombrero Galaxy: Spiral

Elliptical: Most Common Type

Irregular: Magellanic Cloud

How Galaxies Are Classified?• In part by their shapes.• 3 main types: Spiral, Irregular, Elliptical

Spiral Galaxies

• Looks like a pinwheel• Lots of stars• Examples: Milky Way,

Andromeda

Sombrero Galaxy: Spiral

Elliptical Galaxy

• Vary in shape from ball or ovals to flat disks – No arms!

• Contains little dust and gas• Most common galaxy type

Irregular Galaxy• Have no definite shape• Made of mostly dust and gas• Are newer• galaxies….always

making lots of new

stars• Rare

Galaxies…

What kind of

galaxy is this?

What kind of

galaxy are

these…?

What kind of

galaxy is this?

What kind of

galaxy are these?

The Andromeda Galaxy, M31

2.5 million light-years away is the galaxy Andromeda. It is the nearest galaxy to our own, the Milky Way.

Light-Years• Light-year = the distance light travels in

one year• For example, Andromeda travels for 2

million years before it is visible to us on Earth.

• Light travels at a speed of 186,000 miles/second (6 trillion miles/year)