1. THE FORMATION OF THE SOLAR SYSTEM

2. Its all about gravity Gravity can set the particles and dust in a nebula into motion The core of a young star (protostar) acts as an anchor being the largest mass in the nebula The protostar is hot and dense and particles from the nebula begin to gather around it- gravity The spinning nebula begins to contract and smaller pieces build up, if they avoid impact the planetismals can develop to full planets.

3. How it works

4. Evidence to support this theory Think back to the lab we did and think about the disorganized formation this theory implies. Can you think of anything that can support it The many craters on the moon and other planets indicate many collisions occurred in the formation of the universe.

5. What happens to the Nebula? Over time it flattens into a disc-like shape while spinning in one direction Astronomers theorize that any planets forming during this phase would form in the same flat plane and would rotate and revolve around the star in the same way Using technology, astronomers have discovered flattening nebulas of young stars outside our solar system to support the solar nebula theory

6. Extrasolar planets This theory suggests that planets are byproducts of star formation, so planets should be common since we have a sky filled with stars Astronomers have discovered over 300 planets that are orbiting other stars and these are called extrasolar planets Astronomers have used star light level changes to determine the existence of planets-when viewing the star with the planet in-between the viewer and the star, the brightness is changed. In 2008 the first image was taken of extrasolar planets orbiting HR 8799 in the Pegasus constellation

7. HR 8799

8. GALAXIES

9. The Discovery William Herschel (1738-1822) discovered that the milky way was a huge system of stars that today we know is a galaxy Every star that you see on a clear night is part of the milky way A galaxy is a collection of stars, gas dust and planets held together by gravity

10. Galaxy Shapes Spiral Elliptical irregular

11. Understanding the Milky Way Star Clusters –Open clusters--50-1000 stars along main band of the Milky way –Globular clusters--100000 - 1 000 000 stars arranged in a spherical shape around the centre of the Milky way The diameter of the Milky Way –Around 100 000 light years and the shape is disc- like –We know this from radio waves being able to travel through dust and gas between stars of the Milky way –Recall the distance of 1 light year is 9.5 x 10 12 km

12. Star Clusters

13. The Centre of the Milky Way Galaxy Using radio waves again, astronomers discovered that the centre of the Milky Way is surrounded by a bulge of stars (a sphere of globular clusters) The shape of the Milky way galaxy was determined based on its disc-like shape and central bulge of stars, astronomers concluded it is a spiral galaxy. The Sun is approximately 28 000 light years away from the centre region of the galaxy The visible mass estimate is 200 billion solar masses

15. The Local Group The Milky Way belongs to about 40 galaxies called the Local group. The diameter of this group is about 10 million light years The milky way and Andromeda galaxies are the larges galaxies in the group Most of the galaxies in this group are small elliptical

17. Homework Pg 336 #1-3 Pg 366 #1-3 Pg 367 #1-5