Galaxies

Hubble Deep Field – taken by the Hubble telescope above the Earth

What is a galaxy?

• It’s a huge collection of gas, dust, rocky material like planets, icy chunks, and billions of stars

• These stars are held together by the force of gravity

• The Sun, planets, moons, comets, asteroids, etc. that make up the solar system and the stars you see in the sky at night are part of are part of the Milky Way Galaxy

• Galaxies are divided into four different types, determined by their shape:

• Elliptical (shape similar to a football)– Most common

• Spiral (shape similar to a flat pinwheel)– Arms are composed of a lot of gas and dust

and young blue stars (i.e. star formation is ongoing)

Types of Galaxies

Types of Galaxies (cont’d)

• Barred-spiral galaxy– Like a spiral galaxy, but with a thick line in the

centre

• Irregular (no particular shape)– Smaller and less common than spiral or

elliptical

Irregular GalaxySpiral Galaxy

AC

B D

Barred – Spiral Galaxy

Elliptical Galaxy

• Galaxies are moving outwards in the universe– We will learn how scientists have determined

this in another lesson

• Sometimes two galaxies collide and it appears that the big galaxy eats the smaller galaxy

Unusual Galaxies

• Quasars– Stands for QUASi-

stellAR radio source– Very distant objects

that look like faint stars– Brightest objects in the

universe– Give off 100 times

more energy than Milky Way

The Milky Way Galaxy… our home!

Our Home...

• The Milky Way is a spiral galaxy

• our solar system is located on the Orion arm of the Milky Way galaxy

• So we’re actually on the outskirts of our own galaxy

Think About It...

• Our universe is about 14 billion years old• Our solar system formed about 4.6 billion

years ago• We are moving at about 250 km/sec, and

need about 220 million years to complete one orbit around the centre of our galaxy– so our solar system has orbited the galactic

center between 20 - 21 times since its formation

The Bulge

• Our galaxy has a bulge in the center that is home to most of the stars that call the Milky Way home

Scientists believe the Milky Way galaxy is home to more than 200 billion stars!!!!

The Milky Way in

another view

Our Galactic Neighbour

• If you look out towards the constellation of Andromeda, you are looking towards our neighbouring galaxy, Andromeda – This galaxy is 29 million

light years away

• That’s far out… literally

Pleiades

M15 Globular Cluster

Another picture of M15

Some cool star clusters &

constellations

Planets & Stars on Size Scale http://www.youtube.com/watch?v=CubFmoRvwWQ&feature=related&safety_mode=true&persist_safety_m

ode=1&safe=active