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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