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THE FORMATION OF THE SOLAR SYSTEM 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 itgravity • The spinning nebula begins to contract and smaller pieces build up, if they avoid impact the planetismals can develop to full planets. How it works Evidence to support this theory • Think back to the lab we did and think about the disorganized formation this and a theory implies.QuickTime™ Can you think of decompressor are needed to see this picture. anything that can support it • The many craters on the moon and other planets indicate many collisions occurred in the formation of the universe. 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 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 HR 8799 GALAXIES 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 Galaxy Shapes • Spiral • Elliptical • irregular 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 disclike – 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 1012 km Star Clusters 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 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 Homework • Pg 336 #1-3 • Pg 366 #1-3 • Pg 367 #1-5