Chapter 15 – Stars, Galaxies and the Universe

Chapter 15 – History of the Universe Section 4 – Star Systems and Galaxies Standards 4.a – Students know galaxies are clusters of billions of stars and may have different shapes 4.b – Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature and color

Star Systems and Clusters Most stars are members of groups of two or more stars, called star systems (our sun is a single star) Binary star - star system with two stars Eclipsing binary - a system in which one star periodically blocks the light from another

How do they find binary star systems? Dimming Look for a dimming as one star passes in front of the other Gravity Look for a wobble as one star pulls on the other

Planets around other Stars Astronomers found a planet revolving around a star – 51 Pegasi (using the same methods to detect binary stars) video Pegasi-51 was the first planet discovered outside our solar system Now, astronomer have confirmed about 1000 more

Planets around other Stars Astronomers have only been able to find very large planets so far Smaller planets are difficult to see Too much light Not much gravity Planets outside our solar system are called exoplanets

Star Clusters Younger Open Clusters – have a loose, disorganized appearance and contain no more than a few thousand stars Cluster video Globular Cluster – large groupings of older stars, round and densely packed Older Cluster video #2

Star clusters are part of galaxies

Galaxies Galaxy – a huge group of single stars, star systems, star clusters, dust and gas bound together by gravity Many large galaxies (including our own) appear to have huge black holes at their center Quasars – an enormously bright, distant galaxy 10 billion light-years or more away – making them among the most distant objects in the universe Quasar clip

Galaxies – 3 main types Spiral Galaxy- A galaxy whose arms curve outward in a pinwheel pattern Elliptical Galaxy- A galaxy shaped like a flattened ball, containing only old stars Irregular Galaxy- A galaxy that does not have a regular shape

Milky Way Galaxy We live in the Milky Way Galaxy – a spiral galaxy The center is about 25,000 light-years from the sun The center is not visible from earth due to massive clouds of stars, dust and gas between the sun and the center Milky way video clip

Scale of the Universe Universe – all of space and everything in it Scientific Notation – uses powers of ten to write very large or very small numbers in shorter form To express a number in scientific notation, first insert a decimal point in the original number so that you have a number between one and ten To determine the power of 10, count the number of places that the decimal point moved 3,230 light-years = 3.23 x 103 light-years

Scientific Notation The sun takes about 220,000,000 years to revolve once around the center of the galaxy. Express this length of time in scientific notation 2.2 X 108 years The star Betelgeuse has a diameter of 940,000,000 km. Betelgeuse is 427 light-years from Earth. Write each of these figures in scientific notation. 9.4 X 108 km 4.27 X 102 light-years

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