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Name: ______________________________________________________ Period: _______ Date: ____________ How Big Is A Light Year? Directions: In the space below, calculate how large a light year is in miles. Use the speed of light provided by your teacher. C (speed of light) = 1 light year = Outside our solar system, stars are so far away that standard units of measurement like miles and kilometers are awkward to measure these distances, therefore a unit known as the light year is used. A light year is defined as the distance that light travels in one Earth year. Light moves extremely fast, 300,000 km/s or 186,000 miles/second. In one second light can travel around Earth almost four times. Because light travels so very fast, everything appears to happen instantly in our everyday experience. If we are watching the Philadelphia Eagles kick a field goal, we assume that the ball was kicked right at the moment that we saw it. In actuality we must see the light that is being reflected from the ball, and it does take time for the light to travel from the ball to our eyes. If the distance from the ball to our eyes were 10 m, the light reflecting off the ball would take only 300 millionths (.000003) of a second to reach our eyes, thus making it seem instantaneous. Alpha Centauri, the nearest star to the Sun, is over 4 light years away, meaning the light we see from it took over four years to travel to our eyes. It also means that what we see happening at that star is actually what happened four years ago, not what is happening in the star’s present. 1) Light years are used to measure ____________________ rather than time. 2) Imagine that there is a planet with intelligent beings on it that's 20 light years away from Earth. These beings have an extremely powerful telescope and can actually make out details of what is happening on Earth. If they aim their telescope at the White House in Washington, DC, who would they find living there as the president and first lady? 3) If the red giant star, Betelgeuse, is 520 light years away, and it blew up in a supernova 150 years ago, what year would it be when we actually see the explosion? 4) On another imaginary planet, someone is looking through a high powered telescope aimed at Earth, and is observing the birth of America, as Thomas Jefferson pens the Declaration of Independence. How many light years away is the planet from Earth? How many miles away is it? ____________________ light years; _________________________________________ miles 5) Is a light year a useful unit when measuring distances within our solar system? Why or why not? (HINT Pluto is about 4 billion miles away from the Sun.) Famous Astronomers Directions: Match the famous astronomer to the quote that makes the most sense. Tycho Galileo Kepler Ptolemy Hubble Copernicus 1) “I’ve finally worked out a mathematical explanation as to why planets orbit the sun and moons orbit planets. It is gravity that keeps an object in orbit!” 2) “The Earth is the center of the universe, and all of the planets and stars orbit our planet. How do I know? Well, my theory predicts the motion of the planets better than any other theory of my day.” 3) “Using large telescopes, I’ve discovered that all the other galaxies out there are moving away from us; in other words, the universe is expanding, as if it exploded in some sort of ‘Big Bang’! Gee, I sure hope someone names a famous space telescope after me someday!” 4) “I prefer the theory of the sun-centered universe over other theories. This handy device called a telescope has helped me to discover that the planets are not just dots of light, but physical bodies like the Earth.” 5) “After several years of very precise observations, I conclude that our universe is Earth-centered. Furthermore, the sun and the moon revolve around the Earth, while the other planets revolve around the sun.” 6) “For centuries people have been thinking that the Earth is at the universe’s center, but I’m certain that it is, in fact, the sun at its center. And, though it is not an accepted theory these days, I am certain that the planets orbit the sun.” 7) “I do not agree with my mentor’s theory that the sun revolves around the Earth. I have used his precise data to propose another theory in which all of the planets revolve around the sun in elliptical orbits.” 8) “As one of the most famous ancient Greek philosophers, I asked questions about the universe and our place in it. Many people consider me to be one of the first scientists ever.” Newton Aristotle