The Universe and Galaxies

Adapted from:

http://www.west-jefferson.k12.oh.us/EarthandSpaceScience.aspx

Astronomy

The study of objects and matter outside the

Earth’s atmosphere and of their physical and

chemical properties.

What is the Universe?

Universe - sum of all matter and energy that ever has, does, and ever will exist

everything physical that exists in space and time

Cosmology – the study of how the universe began, what it is made of, and how it continues to evolve and change

The Composition of the Universe

(What it is made of…)

Stars, planets, rocks, comets, asteroids,

dark matter, and dark energy

The Composition of the Universe

(What it is made of…)

Dark matter – theoretical unseen and

undetectable mass that adds to the gravity

of a galaxy

Dark energy – theoretical energy that might

be causing accelerated expansion of the

universe

Most of What We See in Space Are

Stars

Stars - huge balls of

hot gases that

emit (gives off)

light

Stars are grouped

together by the

millions and

billions into

galaxies

Astronomical Distance

Measured in light years

Light year - the distance

light travels in one year.

The estimated distance that

light travels in a year is ~6

trillion miles or 10 trillion

kilometers

Astronomical Distance

Astronomical Unit-

The distance from the Earth to the Sun

An estimated 150 million kilometers or 93

million miles, which is equal to 8 light

minutes

We use AU’s as the unit of measure within

our solar system and light years for the

distances within the universe.

Looking into the Past

Time is required for light to travel through

space

Light travels a little over 8 minutes from the

sun to earth

The farther away an object/star is, the longer

it takes for light to get to us, and the older the

light is when it gets to us = “Light is OLD”

We see the past of other stars in the night

sky

Looking into the Past

Light from the nearest galaxy, Andromeda, was

emitted 2.5 million years ago.

Therefore, the images we see of these objects

are how they looked at the time in the past when

their light left them.

The farther away an object is, the older the light

is that we are receiving from it.

Galaxies

Galaxy - grouping of millions or billions of

stars,dust, and gas held together by

gravity

There are an estimated 100 billion

galaxies in the universe

3 Types of Galaxies - classified by shape

Galaxies

Spiral Galaxies- disk shaped with spiral arms of

dust and gas

Dust and gas provide a place for new

stars to form

Young stars are bluish in color gives spiral

galaxies a blue tint

Looks like a pin wheel

Milky Way is a spiral

galaxy

Galaxies

Elliptical Galaxy most common type of

galaxy

Spherical and egg shaped

NO spiral arms,

little dust and gas

Generally have older

stars (reddish in color)

Galaxies

Irregular Galaxy least common type of

galaxy

NO well defined shape or structure

Some have little

dust or gas

Some have lots of

dust and gas

Milky Way Galaxy

The galaxy we live in

Consists of stars and clouds of dust and

gas between stars (interstellar matter)

All the stars we see at night are in the

Milky Way galaxy (about 400 billion stars)

Milky Way Galaxy – side view

• A huge spiraling disk of stars and

interstellar matter 1000 l.y. thick

Milky Way Galaxy – Overhead View

A huge bulge in

the center

10,000 l.y. thick

Where Are We

In The Galaxy?

Our solar system

is about halfway

between the

center and the

edge of the

galaxy (26,000

light years from

the center)

Milky Way Galaxy

The nearest

galaxy to ours

is the

Andromeda

galaxy 2.6

million l.y. away

Gravity Holds Galaxies Together

Dust, gases, and stars are attracted to

each other by gravity

Galaxies are grouped

into clusters groups

of galaxies bound

together by gravity

Gravity Holds Galaxies Together

Milky Way and Andromeda galaxies are in

a cluster of ~45 galaxies called the

“Local Group”

Superclusters - have

thousands of galaxies

largest structure

in the universe

Universe Origins

The universe is composed of matter and energy.

All of the matter in the universe now was in the

universe when it formed.

The ‘Big Bang’ Theory is currently the most

widely accepted theory among scientists on the

origins of the universe.

Astronomers and cosmologists have evidence

regarding this theory.

Big Bang Theory Basics

Main Premise:

The universe began with a gigantic explosion (expansion of matter) ~13.7 billion years ago

Nothing existed before this No time, NO space

Out of nothingness came everything in the universe and it started to expand

Big Bang Evidence

Looking at the oldest stars

Cosmic background radiation that astronomers have picked up from various EM wave capturing technologies

By measuring the rate the Universe is expanding-astronomers what is called “red shift.”

As the universe expands and galaxies move apart, the wavelength of light given off by those galaxies is stretched.This shifts the light toward the red end of the spectrum.

The more distance or faint a galaxy the more rapidly it is moving away from Earth.