1. Section 3: The Universe “Gaining a better understanding of the universe gives us more insight into the possible origin of everything around us”

2. Galaxies Galaxy: huge collection of stars, planets, gas, and dust held together by gravity Galaxy: huge collection of stars, planets, gas, and dust held together by gravity Milky Way is a galaxy that includes our solar system Milky Way is a galaxy that includes our solar system Appears as a milky, hazy white band but it is actually a huge number of stars Appears as a milky, hazy white band but it is actually a huge number of stars Galaxies form because of gravity Galaxies form because of gravity

3. The Milky Way

4. All Shapes and Sizes…

5. Shapes of Galaxies Spiral Galaxy: looks like a pinwheel when viewed from above Spiral Galaxy: looks like a pinwheel when viewed from above Long “arms” spiraling out from centre core Viewed from the side, looks like a dinner plate with a bulge in the centre Ex. Milky Way

6. Shapes of Galaxies Elliptical galaxy: Range in shape from perfect sphere to stretched out ellipse Elliptical galaxy: Range in shape from perfect sphere to stretched out ellipse Contain some of the oldest stars in the universe Contain some of the oldest stars in the universe Makes up >50% of universe Makes up >50% of universe Largest known galaxies are elliptical Largest known galaxies are elliptical Ex. Centaurus A Ex. Centaurus A

7. Centaurus A

9. Shapes of Galaxies Irregular galaxy: Do not have a regular, recognizable shape such as a spiral or a central bulge Irregular galaxy: Do not have a regular, recognizable shape such as a spiral or a central bulge Lack of shape Lack of shape “The Bird” “The Bird”

10. Star Clusters “Open Cluster” “Open Cluster” 50 -100 stars 50 -100 stars Appear along the main band of Milky Way Appear along the main band of Milky Way “Globular Cluster” “Globular Cluster” ≥100 000 stars Arranged in distinctive spherical shape Appear around center of Milky Way Collection of Stars held together by gravity Collection of Stars held together by gravity

11. Open Cluster

12. Globular Cluster

13. More Milky Way… Scientists have mapped our galaxy using radio waves. Scientists have mapped our galaxy using radio waves. Gigantic system of stars, seen as a white band across southern horizon Gigantic system of stars, seen as a white band across southern horizon Diameter: 100 000 light years Diameter: 100 000 light years Recall: 1 light year – distance light travels in 1 year Recall: 1 light year – distance light travels in 1 year 9.5 x 10 12 km 9.5 x 10 12 km Centre of Milky Way is a sphere of globular clusters Centre of Milky Way is a sphere of globular clusters

14. More Milky Way… William Herschel counted stars to figure the apprx. shape of M.W. William Herschel counted stars to figure the apprx. shape of M.W. Flat disc with sun in centre Flat disc with sun in centre Harlow Shapley used star clusters to figure out that the sun (and thus our solar system) is nowhere near the centre Harlow Shapley used star clusters to figure out that the sun (and thus our solar system) is nowhere near the centre

15. The Sun is apprx. 28 000 light years away from the centre of the Milky Way (the bright bulge) The Sun is apprx. 28 000 light years away from the centre of the Milky Way (the bright bulge)

16. The Shape of the Milky Way 2 major spiral arms, numerous minor arms 2 major spiral arms, numerous minor arms Est. mass: Est. mass: 200 000 000 000 solar masses

17. The Local Group Milky Way belongs to a group of ~ 40 galaxies known as the Local Group Milky Way belongs to a group of ~ 40 galaxies known as the Local Group Diameter of the Local Group is ~ 10 million light years Diameter of the Local Group is ~ 10 million light years The Milky Way and Andromeda galaxies are the biggest within the Local Group The Milky Way and Andromeda galaxies are the biggest within the Local Group

18. The Local Group

21. The Local Group is a cluster of galaxies The Local Group is a cluster of galaxies 4 – 25 clusters = a supercluster! 4 – 25 clusters = a supercluster! A gigantic cluster of galaxies, hundreds of millions of light years in size A gigantic cluster of galaxies, hundreds of millions of light years in size

22. Class Work Think-pair-share! Think-pair-share! In pairs, answer questions 1-4, 7-8 In pairs, answer questions 1-4, 7-8 Finish for HW Finish for HW