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Our Solar System – a Speck in the Milky
• Our galaxy is about ____________in diameter
▫ What’s a ly again?
• It is _______________thick at its widest
point near the core
• Our solar system is very tiny compared to the
whole Milky Way
• A beam of light from the Sun would take
_____________ to cross the entire Milky Way
▫ But it takes only _________to get to Neptune! :o
Our Milky Way
•Looks like two fried eggs stuck
back to back (from the side)
•Looks like a giant whirlpool
(from the top)
•Our Sun takes about 220 million
years to travel once around the
centre of the galaxy
•This means that in millions of
years, people will see different
stars at night
•If our solar system was a single
bean, the Milky Way would be a
bit larger than the area of Lake
Our Milky Way
_________________ Galaxy
•One of the ______________
galaxies to us
•You can see it from Britain
•It is __________________
•The most distant galaxies are
•When light left them, the Earth
did not exist!!
Properties of Galaxies
• All galaxies contain _________,
______________ and ____________
• More dust means more ___________
▫ Stars form from dust and gases present in
▫ __________________ galaxies have less dust
because it has all been used up in star-making
Properties of Galaxies
1. Black Hole
It is a region of space where ____________ is so
strong that nothing (not even light) can escape
It’s believed that each galaxy contains __________
supermassive black hold at the _____________
Milky Way: at centre, many stars are orbiting around a
point in space that seems empty
Affects its surroundings by __________________
Can pull a star right into it, destroying the star
This will increase the ____________ of the black hole
Milky Way: ours has a mass of
____________________ stars like our Sun
When two galaxies collide, the black holes will _____
Properties of Galaxies
2. Dark Matter
It is matter in the universe that is ___________
It does not interact with _______or other radiation
Astronomers think that __________ of the
universe is filled with dark matter
Unexpected _______________ of galaxies
Milky Way: stars revolve around centre so fast, they
should be flung off but aren’t
Most of the ______________ in the universe is
thought to be produced by ________________
Properties of Galaxies
3. Star Clusters
This is a ______________________ of stars
Has a concentration of stars in a smallish region
of space
Two types:
1. ______________ Cluster
Contains a few hundred to a few thousand stars
One of the _____________star groups in a galaxy
2. ____________________ Cluster
Contains hundreds of thousands of stars, drawn
together by the stars’ gravity
One of the _____________star groups in a galaxy
Properties of Galaxies
Open Cluster
Globular Cluster
Galaxy Shapes
• Galaxies are commonly classified according to
four main shapes:
Galaxy Shapes
1. Spiral & Barred Spiral
Have spiral-shaped _____coming out from the centre
Half of all spiral galaxies have a bar across the ________
A typical spiral galaxy completes a full rotation once about
every __________________________
Most spiral galaxies have hundreds to thousands of star
These are called barred spiral galaxies (E.g.: Milky
Due to the dust and gases between stars (breeding ground for
new stars)
At the core, has a “_______________” with mostly old
stars (not enough dust an gases here)
Galaxy Shapes
3. Elliptical Galaxies
Looks like a _________________________
Can look almost _______________
Can look ___________________________
Can look long and cylindrical like a _________
Happens when spiral galaxies _________
These are the _____________galaxies
Don’t have a lot of dust  fewer young stars
Galaxy Shapes
4. Irregular Galaxies
Neither spiral nor elliptical
No ________________shape
May have happened because...
Two galaxies ____________________
Two galaxies got _______ enough that the gravity
of one ______________ stars from the other
Galaxy Shapes
Spiral Galaxy
Barred Spiral Galaxy
Galaxy Shapes
Elliptical Galaxy
Irregular Galaxy
Learning Checkpoint
1. What is a galaxy?
2. What is thought to be at the very centre of all
3. What is dark matter?
4. Sketch the general shape of a spiral galaxy as
viewed from the side and then as viewed from
5. State one possible way that elliptical galaxies
Galaxy Clusters
• The universe does not end at the Milky Way!
• The Milky Way is part of a group of ________
▫ This is called a galaxy cluster
▫ Ours is called the ___________________
 More than _____________ stars are inside it
• The Local Group is part of the Local Cluster
• The Local Cluster is part of the Local
Galaxy Cluster
Miss Strilchuk
700 Main Street West
Milky Way
Local Group
Local Cluster
Local Supercluster
The Universe