1. Galaxies

2. Announcements Chapter 4 quiz on Thursday or Friday
Think about your project ideas and how you would like to proceed.
Homework will be on Energy (chapter 5) with a short quiz to follow.

3. Goal of the class
To understand our galaxy and how it compares to other galaxies
Question of the day: What keep galaxies together?

4. Galaxy Galaxies are large regions of stars, gas, dust and dark matter
The gravity of each of these parts largely hold everything together
Most of the mass may be dark matter
All of the mass rotates around the centre.
A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter, an important but poorly understood component.[1][2] The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with as few as ten million (107) stars[3] to giants with one hundred trillion (1014) stars,[4] each orbiting their galaxy's own center of mass.

5. Types of Galaxy Spiral Galaxies Elliptical Galaxies Irregular Galaxies
Spiral shape
May have large bars
Most stars being formed are in the spiral arms
Elliptical Galaxies
Contain mostly older stars
Round smooth shape
Irregular Galaxies
Don’t have a regular shape
Have many bright young stars and gas and dust to start new stars
Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology. A common form is the elliptical galaxy,[6] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Those with irregular or unusual shapes are known as irregular galaxies[7] and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merger, sometimes induce significantly increased incidents of star formation leading to starburst galaxies.
There are probably more than 170 billion galaxies in the observable universe

6. Spiral Galaxy
Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology. A common form is the elliptical galaxy,[6] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Those with irregular or unusual shapes are known as irregular galaxies[7] and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merger, sometimes induce significantly increased incidents of star formation leading to starburst galaxies.
There are probably more than 170 billion galaxies in the observable universe

7. Elliptical Galaxy
Galaxies have been historically categorized according to their apparent shape, usually referred to as their visual morphology. A common form is the elliptical galaxy,[6] which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped with dusty, curving arms. Those with irregular or unusual shapes are known as irregular galaxies[7] and typically originate from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in a merger, sometimes induce significantly increased incidents of star formation leading to starburst galaxies.
There are probably more than 170 billion galaxies in the observable universe

8. Irregular Galaxy

9. Quasars

10. Quasars All galaxies have a supermassive black hole at the center
Some types of galaxies have the black holes pulling in gas and dust
These are called quasars
The gas and dust heats to millions of degrees and releases electromagnetic radiation

11. Milky Way Our galaxy is the Milky Way It holds over 400 billion stars
It is a spiral bar galaxy
It holds over 400 billion stars
One rotation of the sun in the Milky Way takes about 225 million years

12. Solar System
The Earth is in the Solar system that is a part of the Virgo super cluster
The Solar system is one of the spiral arms of the milky way
The sun is about 27,000 light
years from the center

13. Centre of our Galaxy
The supermassive black hole at the centre of our galaxy in the Sagittarius A* system has million times the mass of the sun

14. Order of things

15. Vocabulary
Dark matter – A hypothetical type of matter invisible to electromagnetic radiation
Light year – The amount of distance light crosses in one year x 1012 km

16. Homework
Page in your workbook on energy