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Name: Date: Period: Astronomical Distances 1. Imagine you are drawing a map of your exact position in the Milky Way Galaxy. You decide you are going to start with the small scale of the classroom and then work your way out to where you are in the Milky Way Galaxy. What units of measurement would you use to describe your positions at each level? a. Classroom: b. School: Meters, kilometers or yards c. City: d. State: Hundreds of miles e. Country: Thousands of Miles f. World: g. Solar System: h. Galaxy: 2. If you were measuring our Solar System, would miles or kilometers be the best unit of measurement? Explain your answer. Astronomical Units: An Astronomical Unit was designed to measure the distance of celestial objects with respect to Earth’s distance from the Sun. One Astronomical Unit is equal to the distance from Sun to the Earth, which is 149,598,770 km. Using the table provided below, fill in the blanks to determine the distances to our fellow planets in the Solar System using Astronomical Units. *Round to the nearest hundred thousand for your calculations. Example: 3,098,000 3,100,000 Diameters & Distances from the Sun Diameter (km) SUN MERCURY VENUS EARTH MARS JUPITER SATURN URANUS NEPTUNE PLUTO Distance (km) Astronomical Units (AU) 1,391,400 0 0 4,878 57,900,000 0.39 12,104 108,209,000 12,756 149,598,770 6,794 227,900,000 142,984 778,200,000 120,536 1,429,200,000 51,118 2,875,000,000 49,528 4,504,400,000 2,302 5,915,800,000 1 Light years: How far does light travel per minute, per hour, per hour and per YEAR? Did you know that light travels at 186,000 miles/second (300,000 km/second)! The Earth is about 25,000 miles around. That means that light travels around the Earth 7.5 times in one second! 25,000 miles 186,000 miles/second = 0.134 seconds for = 7.44 times OR light to travel around the 186,000 miles/second 25,000 miles Earth Per Minute Per Hour Per Day miles/min 669,600,000 miles/hour 186,000 miles/sec x 60 x x x “Light minute” “Light Year” “Light Hour” “Light Day” Per Year miles/day 365.25 3. Based on your calculations, what is the definition of one light-year? Objects Time for Light to Travel Sun to Earth Earth to Moon 1.3 seconds Earth to Saturn 1.2 hours Earth to nearest star (Alpha Centauri) 4.3 years Earth to North Star 430 years Earth to nearest galaxy (Andromeda) 2 million years Distance in Light-units 8 “lightminutes” 1.3 “lightseconds” “light-hours” Distance in Miles ~241,800 miles ~803,520,000 miles 4. Why do astronomers use AU (Astronomical Units) instead of miles or kilometers? 5. Why would astronomers use light years instead of AU? 6. How many AU are there in one light year? Challenge: How many miles is it across the Milky Way Galaxy? (Our Milky Way Galaxy is about 100,000 light years across)