Download The Universe

The Universe
PHYSICAL SCIENCE
Our Place in the Universe
Scale of the Universe
Exploring the Universe


Star – a large glowing ball of gas in space

Generates energy through nuclear fusion in its core

The Sun is the closest star to use, and is of fairly average size

Formed by gravity

Why do stars have to be massive in order to be a “star”?
Distances to the Stars

Space distances are so huge normal units aren’t very useful

Light-year (LY) - The distance that light travels through a vacuum in one
year

Astronomical Unit (AU) – 1 AU = Distance from Sun to Earth = 93 million miles

How do we measure the distance to the stars?
How to measure distance to a star


Parallax – Triangulation

Only works on stars within 400 ly

Look at a star when Earth is in two diff positions and see how its position
relative to the stars behind it change
Scientists have developed other ways to estimate distances to
further stars
Properties of Stars

Astronomers classify stars by their color, size, and
brightness

Color
 Indicates
 Red
stars temperature
– Coolest
Blue- Hottest
Star Color


Color and Temperature

A star’s color indicates the temperature of its surface.

The hottest stars, with surface temperatures above 30,000 K, appear
blue.

The surfaces (photospheres) of relatively cool red stars are still a toasty
3000 K or so.
Stars with surface temperatures between 5000 and 6000 K appear
yellow, like the sun.
Spectral Classes of Stars
Star Brightness

Apparent Brightness



How bright it looks from Earth
Absolute Brightness

How bright it actually is

It’s like measuring the brightness of all the stars
when they are all equally far from you

Size and temperature
Light becomes fainter with distance
Size & Mass

Once astronomers
know a stars
temperature and
absolute brightness,
they can estimate its
diameter and then
calculate volume

Scale of the
Stars

Scale of the
Universe
HertzprungRussel
Diagram

Used to estimate sizes of
stars and their distances,
and to infer how stars
change over time

90% of all stars found on
main sequence

Relates brightness, Temp,
Size, & Color
Composition of Stars


Absorption Lines

Scientists determine the chemical makeup of stars by looking at Absorption lines

Spectrograph – instrument that spreads light from a hot glowing object into a spectrum

Different elements absorb different wavelengths of light. Thus removing them from the
spectrum. The blank spaces (absorption lines) in the spectrum below represent different
elements in that star

Each star has its own unique spectrum.
Most Stars have a chemical makeup that is similar to the Sun, with H and He together
making up 96 to 99.9% of the stars mass
Why are Stars Round?

Gravity tries to get everything as close to the center
as possible…. The only way to achieve this is if it is in a
spherical shape

Star’s are held in balance by Two Forces

Gravity - Pulls star inwards

Thermal Pressure from Nuclear Fusion– Pushes star
outward

The relative strength of these determine the stars size.

These two forces are balanced before a star dies

Nuclear Fusion – Two atoms are pushed together so hard
they ‘fuse’ into one and create a different element
Life Cycle of stars
Death of a Star

Low & Medium Mass Stars


Planetary Nebula  White Dwarf
High Mass Stars

Supernova

Neutron Star

Black Hole
When a star dies….

White Dwarf (C.P. Powerpoint)

Neutron Stars

Black Holes
Groups of Stars

Galaxy

Huge group of individual stars, star systems, star
clusters, and gas bound together by gravity

Our Galaxy – Milky Way

Each consists of Billions of stars…. Sometimes Trillions

Four types – Spiral, Barred-Spiral, Elliptical, Irregular
Location of
solar system
Central bulge
Nucleus
Overhead View of Our Galaxy
Disk of spiral arms
containing mainly
young stars
Halo containing
oldest stars
Central bulge
containing mainly
older stars
Nucleus
Side View of Our Galaxy
Big Bang Theory

Explanation

The universe came into existence in a
single moment, an event called the Big
Bang

The event happened 13.7 Billion years
ago

All matter and energy were
concentrated into a single infinitely
small point

Timeline of the universe

Video
Big bang
occurred 13.7
billion years ago.
First stars and
galaxies formed
200 million years
after big bang.
Solar system
formed 4.6 billion
years ago.
Earth today
Evidence for Big Bang

Edwin Hubble -Red Shift of Galaxies

Light from most galaxies undergoes a
redshift. Light is experiencing Doppler effect
and shifting to longer wavelengths (red
light). This means it is moving away from us.
This is noticed in most galaxies.

Shows universe is expanding

By looking at the rate its expanding we can
calculate how long its been expanding, thus
inferring the age of the universe

More distant galaxies are moving away
from Earth faster than closer galaxies

Cosmic Microwave Background Radiation

Video – Evidence for Big Bang CMB

Video – Red Shift of Galaxies

Rubber band activity Pg. 855
Doppler Effect with Light Waves
Stationary
Moving
towards
Moving
away
Continued Expansion

All galaxies are expanding away
from all other galaxies

Further way the galaxy the
greater the expansion

Will Universe continue expanding
forever??

Recent evidence shows that the
rate of expansion is actually
increasing
Cosmic Microwave Background Radiation

Faint distant glow
detected in every
direction

Energy produced during
the big bang still
travelling through the
universe
Matter in the Universe

Dark matter
 Matter
that does not give off light
 Cannot
see it but we know its there
because of its gravitational effects