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How Far is a Light Year? Claire Hodgin – Science Instructional Coach University of Texas – University Charter Schools Armosky and Hodgin University of Texas at Austin, 2009

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Engage Powers of Ten About the Relative Size of Things in the Universe What was the smallest to the largest distance on the video? ,000,000,000,000,000,000,000,000,000,000,000,000,000 m

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Explore If we could shrink the Sun to the size of this balloon, how big would the Earth be? messagesfromearth.wordpress.com

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Our Solar System kiroastro.com

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What is one way to measure a planet or star? By the Diameter of the sphere…

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Diameter of a planet… The distance from one edge to the opposite edge Diameter of a sphere

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It would take 108 Earths laid side-by- side to go across the Suns diameter messagesfromearth.wordpress.com findfreeclipart.com

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Finding the Earth/Sun Diameter Ratio The Earths diameter is 12,756,000 meters or ~ 1.3 X 10 7 m The Suns diameter is 1,400,000,000 meters or ~ 1.4 X 10 9 m The ratio of the Earth : Sun diameter is 1.3 X 10 7 m : 1.4 X 10 9 m Simplify the ratio X 10 7 m : 1 m 1.4 X 10 9 m : 108 m Earth to Sun Diameter ratio is 1 : 108

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Actual Distance from the Sun to the Earth

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If we use the same scale as we used for the SIZE of Sun and Earth… How far apart would the Sun and Earth be in our model? Sun Diameter Sun to Earth Distance Model.45 m = XModel Actual1.4 x 10 9 m1.5 x mActual Cross multiply and x = 4.8 x 10 1 m (48 m) or ~ 50 m

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Distance from the Sun to the Earth in our model

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Lets take a field trip -To build a model to scale the Sun will be a 450 mm balloon the Earth will be a 4 mm lentil and they will be 50 meters apart

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Explain The Milky Way Galaxy is about 100,000 light years across Powersof10.com

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DISTANCE One light-year is the DISTANCE that light travels in one year If we are going to find out HOW FAR is a Light Year HOW FAR is a Light Year, we need to know two things… -The speed of light, measured in meters per second and -The number of seconds in a year

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What is the fastest speed in the universe? The Speed of Light What is the speed of light? (abbreviated c) 300,000,000 meters per second 300,000,000 meters per second or 3 X 10 8 m/s (remember the line in Powers of Ten?)

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How Many Seconds in a Year? 60 seconds per minute X 60 minutes per hour X 24 hours per day X days per year = the number of seconds per year

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On the Graphing Calculator… Turn on and press Mode At the top row are the words: Normal NormalSciEng And the Normal is highlighted in black Arrow right to Sci until it is highlighted, and press Enter Quit (2 nd Mode), and now all of your calculations are in Scientific Notation (Powers of Ten)

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In science we call this Dimensional Analysis, in math Unit Conversion 60 s60 min24 hr days3.2 x 10 7 s 1 min1 hr1 day1 yr Lets try this on the graphing calculator =

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So How Far is a Light Year? Multiply the Speed of light (m/s) by the number of seconds per year (s/yr) = number of m/yr 3 x 10 8 m/s X 3.2 x 10 7 s/yr = 3 2 nd LOG 8 ) X nd LOG 7 ) Enter 9.5 x m/yr Or 9,500,000,000,000,000 meters Thats Nine Quadrillion, Five Hundred Trillion Meters

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How long does it take light to get from the Sun to the Earth? 8 minutes It takes 16 minutes to go there and back

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If we use the same scale as we used for the SIZE and DISTANCE of Sun and Earth… How long would a light year be in the model? Sun Diameter Light Year Model.45 m = XModel Actual1.4 x 10 9 m9.5 x mActual Cross multiply and x = 3.1 x 10 6 m

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3.1 x 10 6 meters Thats 3.1 x 10 3 kilometers! Thats 3 times wider than Texas! Thats too much tape!

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Lets change the scale of our model. What is the new scale factor so that 1 light year fits inside a 50 meter paper strip? Light Year Distance Sun Diameter Model50 m = XModel Actual9.5 x m1.4 x 10 9 mActual Cross multiply and x = 7.4 x m

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