STARS & GALAXIES

Chapter 27

Our Solar System

The Sun

The Planets Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

Special Regions Asteroid belt

Between Mars and Jupiter

1000’s discovered

Ceres, Pallas, Vesta, Juno

Kuiper Belt Neptune to beyond

Pluto

short period comets

Oort Cloud Beyond the Kuiper

Belt to approx. 1 Lyr

long period comets

The Astronomical Unit

A convenient unit for measuring solar system distances

1 AU = average distance between the earth and sun

1 AU = approx 150,000,000 kilometers

1 AU = approx 93,000,000 miles

1 AU

The Inner Solar System

Mars 1.5 AU

Earth 1 AU

Venus 0.6 AU

Mercury 0.3 AUMe

VE

Ma

J1 AU

The Asteroid Belt

Between the

orbits of Mars

and Jupiter

1000’s known

Also called

Minor Planets

Me

Ve

Ma

J1 AU

Outer Solar System

P

J 5 AU

S 10 AU

U 20 AU

N 30 AU

P 40 AU

Pluto’s orbital inclination is the greatest at 17° to the Plane of Ecliptic

P

P lane of

Elliptic

J S UN

top

viewside view

Kuiper Belt and Oort Cloud

The Oort Cloud

extends to

50,000 AU’s

The Kuiper belt

extends to just

beyond the

orbit of Pluto

NJ S U NP

Oort Cloud

Kuiper Belt

Beyond the Solar System

The Celestial Sphere

Stars

Milky Way

“How Far?” is the key question

The objects we can see are incredibly

distant.

Beyond that are even more objects!

Distance to the Stars

Light Year—the distance that light travels in one year

The speed of light is 186,000 mps, so light travels 6 trillion miles in one year

Light from the sun takes about 8 minutes to reach earth.

The Light Year

A convenient unit for interstellar distances

uses (light speed = c) to gauge distance.

1 Lyr = distance traveled by light in one year

c=186,000 miles/sec or 300,000 km/sec

1 Lyr = 6,000,000,000,000 miles

1 Lyr = 10,000,000,000,000 kilometers

The Parallax Another convenient unit for interstellar distances uses

Parallax to gauge distance

If the angle x is 1” of arc, the distance to the star is 1 parallax second or 3.2 light years. This is a very small angle!

X

earth at time = t

earth at time t + 6 mo..

distant star

Try This at Home

Parallax—one method to determine the distance between stars and the earth.

The thumb exercise

The Milky WayIt is a spiral galaxy and it is one of billions of

galaxies

The diameter is about 100,000 light years.

The galaxy is about 10,000 light years thick.

The sun is located about 30,000 light years from the center.

What is a star??

A body of gases that gives off a tremendous amount of radiant energy in the form of light and heat

Spectrometer

A spectrometerseparates light from stars into different wavelengths in order to determine composition and temperature of the stars

Star Temperatures

Blue stars have a temp. as high as 50,000 C

Cool it off

Red starshave an average temp. of 3,000 C

The Average Sun

Yellow stars, like the sun, average about 5,500 C

The North star is 700 light years

away.

The size of stars

Very large stars are called giants or Supergiants

A small star would be called a dwarf, a typical white dwarf star would be the size of earth

Stellar Evolution

In the 1st stage a star begins as a Nebula.

It is a cloud of gas and dust (ex. Orion Nebula)

It is usually composed of 70% hydrogen, 28% Helium, and 2% heavier elements

There are 3 stages to

the Life of a Star

Main-Sequence Stars The 2nd and longest stage of

a star is the main-sequence stage. Energy is generated in the core of the star as hydrogen atoms fuse to become helium atoms.

For ex. when 1g of hydrogen is converted into helium, the energy released is enough to keep a 100 watt bulb burning for 3,000 years.

Why doesn’t a Star just

Blow Up?

The star does not expand

b/c gravity pulls its matter inward.

What Then?

A star enters its 3rd stage when almost all of the hydrogen atoms within its core have fused into helium atoms.

Then It Blows Up!!

Nova— a white dwarf star that has a large explosion that releases energy, gas, and dust into space.

Supernova— a star that has such a tremendous explosion that it blows itself apart.

Black Holes Black Hole— Occurs when the core of a star is

crushed by its own gravity and leaves a hole in space.

STAR GROUPS

Astronomers recognize 88 constellations in the sky.

We use these 88 constellations to divide the sky into sections like a road map.

There are others like:

Orion, the

Great Hunter

The Big Dipper, Ursa Major

The Little Dipper, Ursa Minor

Galaxies

Galaxies— are the major components of the universe, they are made up of groups of stars bound together

by gravitational attraction.

A typical galaxy is about 100,000 light-years in diameter and contains 100 billion stars.

Large Star Clusters

Galaxies can be detected

by the Hubble Space

Telescope 12 billion Lyrs

distant

Quasars are the result of

young galaxies going

through a youthful phase.

Light from the most distant

quasars and galaxies is over

10 billion years old

Which Galaxy do we live in?

The Milky Way

The Milky Way Galaxy

Solar

Neighborhood

100,000 Light Years

10k Lyr

Types of Galaxies

Spiral galaxy—this type of galaxy has a nucleus of stars and flattened arms of stars that spiral around the nucleus.

Galaxies

Elliptical galaxy—they are very bright in the center and do not have spiral arms. They have no young stars and very little dust and gas.

Galaxies

Irregular galaxy—this galaxy has no particular shape. They tend to be smaller and fainter than the other types of galaxies.

The Milky WayIt is a spiral galaxy and it is one of billions

of

galaxies

The diameter is about 100,000 light years.

They galaxy is about 2,000 light years thick.

The sun is located about 30,000 light years from the center.