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Section 3: The Universe

Section 3: The Universe. “Gaining a better understanding of the universe gives us more insight into the possible origin of everything around us”. Galaxies. Galaxy: huge collection of stars, planets, gas, and dust held together by gravity Milky Way is a galaxy that includes our solar system

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Section 3: The Universe

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  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 • 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 • 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 • 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 • Contain some of the oldest stars in the universe • Makes up >50% of universe • Largest known galaxies are elliptical • Ex. Centaurus A

  7. Centaurus A

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

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

  10. Open Cluster

  11. Globular Cluster

  12. More Milky Way… • Scientists have mapped our galaxy using radio waves. • Gigantic system of stars, seen as a white band across southern horizon • Diameter: 100 000 light years • Recall: 1 light year – distance light travels in 1 year • 9.5 x 1012 km • Centre of Milky Way is a sphere of globular clusters

  13. More Milky Way… • William Herschel counted stars to figure the apprx. shape of M.W. • 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

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

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

  16. 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 • The Milky Way and Andromeda galaxies are the biggest within the Local Group

  17. The Local Group

  18. The Local Group

  19. The Local Group

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

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

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