What is a galaxy?

What is a galaxy?

Lesson aims:

1. Find out what a galaxy is

2. Discuss how galaxies are formed

3. Watch and discuss a video about the Milky Way Galaxy

WARM-UP

What is a galaxy?

What galaxies do you know? 

Have you ever visited an observatory?

If not, what would you look at if given the opportunity to look through a telescope? A planet? The moon? A star? A galaxy?

What is a galaxy?

• A massive and gravitationally bound system which is comprised of stars (like the Sun), stellar remnants (compact stars), an interstellar medium of gas and dust, as well as the important, but misunderstood, dark matter - a matter hypothesised to account for gravitational effects that appear to be the result of invisible mass.

Galaxy formation

Gas clouds clump together due to the gravitational pull of matter As the matter gets drawn together, it starts to spiral downwards into the central mass The center becomes squeezed typically until a black hole forms Over time, the galaxy might slowly stop spinning and become elliptical (оптекаемый) Galaxies may collide with other galaxies to form different shapes

Let's watch how it is formed

Galaxy Classification

• Galaxies are classified by their shapes and how distinct those shapes are:

Answer the questions

• What is a galaxy?

• How is it formed?

• What are the types of galaxies?

Why Milky Way?

• The Milky Way gets its name from a Greek myth about the goddess Hera who sprayed milk across the sky. In other parts of the world, our galaxy goes by other names. In China it's called the “Silver River,” and in the Kalahari Desert in Southern Africa, it's called the “Backbone of Night.”

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Watch the video and answer the questions

Answer the questions

• How old is our galaxy? 

• How much does light take to cross from one side to the other? 

• Why is it tough to see the centre of our galaxy?

• What is there in the centre?

• What are the three largest galaxies in our local group?