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History of the Universe (in 10 minutes) https://www.youtube.com/watch?v=-Ip5BAEfZuA Sun and Space Notes 8.8B recognize that the Sun is a medium-sized star near the edge of a disc-shaped galaxy of stars and that the Sun is many thousands of times closer to the Earth than any other star The Sun § The sun is a medium size star § It appears larger than the other stars because of its relative nearness to the earth § It consists of about 70% Hydrogen, 28% Helium and 2% of metals such as iron. Size § The sun is 1,390,000km in diameter ú You could fit 1 million earths inside the sun The planet Venus just passing in front of the Sun It would take 108 Earths laid side-byside to go across the Sun’s diameter Characteristics of the Sun – Teacher’s Domain Relative Sizes Mass § The mass of the Sun is about 2 x 1030 kilograms § It is one of the larger stars in our Milky Way galaxy § The mass of the Sun is over 300,000 times greater than that of the Earth Distance § The Sun is 149,600,000 km (93 million miles) from the Earth ú Since the speed of light is 303,000 km/sec (186,000 miles/second), it takes the light slightly over 8 minutes to get from the Sun to the Earth The Sun’s Location It is located in the outer reaches of the Milky Way, which is a grand spiral galaxy. Astronomers think has four major spiral arms: Perseus, Cygnus, Scutum-Crux, Sagittarius. The Sun is located on Orion’s arm, which is thought to be an offshoot of the Sagittarius Arm. Temperature § Its temperature is extremely hot, with the surface being about 5000° C and the center core at 15,600,000° C. The high temperature in the core, along with extreme pressure from the Sun's mass, result in nuclear fusion reactions. Nuclear fusion converts hydrogen to helium producing energy The Sun in Action § Astronomy Now – recent solar flare – March 11, 2015 § Inside the Sun Importance of the Sun § Without the Sun, the Earth would not be able to support life § It is the main source of energy for earth § It provides light and heat § It’s necessary for plants to carry out photosynthesis Space, just how big is it? § Animation: The Scale of the Universe Powers of Ten 8.8D model and describe how light years are used to measure distances and sizes in the universe The Milky Way § The Milky Way is a cluster of stars, called a galaxy § It contains hundreds of billions of stars § If you traveled at the speed of light for about 2 million years, you would reach the next galaxy – the Andromeda Galaxy § There are billions of galaxies in the universe Distance to Stars § Astronomers use light-years and astronomical units to measure distance ú A light-year is the distance that light travels in one year ú In space, light travels at a speed of 300,000km per second § A light year is about 6 trillion miles or 9.5 million million km Light Years Explained MIT camera captures light at a trillion frames per second 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 § A light year is the distance light travels in a vacuum in one year (An Earth year that is, 365.25 days) Stars Key Idea The light-year is a unit of distance, not time! The Milky Way Galaxy is about 100,000 light years across, we are about 26,000 light years away from the center. Powersof10.com Astronomical Unit § The distance of the Sun to the Earth is called an Astronomical Unit (AU) and is sometimes used to denote large distances that are less than a light year A light year is about 63,241 astronomical units Sun to Earth Distance 1 Astronomical Unit (AU) 93,000,000 Miles Other planet distances in astronomical units (from the sun to that planet) Body Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto AU .39 .72 1.0 1.5 5.2 9.5 19.2 30.1 39.5 Check for understanding: § If the nearest star is 4 light years away how many miles away is it? A light year means 6 trillion miles. Think about that for a moment. If you go outside tonight and shine a flash light at the sky, in the next one year that light will travel 6 trillion miles. 6 trillion x 4 light years = 24 trillion miles! Check for understanding: § How long will it take for the light from that star (that is 4 light years away) to travel to the Earth? Four years. Remember, a light year is the distance that light can travel IN A YEAR! Light year and Time § Using a light year as a distance measurement has another advantage -- it helps you determine age. § Let's say that a star is 1 million light years away. The light from that star has traveled at the speed of light to reach us. Therefore, it has taken the star's light 1 million years to get here, and the light we are seeing was created 1 million years ago. § So the star we are seeing is really how the star looked a million years ago, not how it looks today. In the same way, our sun is 8 or so light minutes away. If the sun were to suddenly explode right now, we wouldn't know about it for eight minutes because that is how long it would take for the light of the explosion to get here.