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What are comets? Learning Target for 10/19 1. 2. 3. I can describe the make up of comets I can model a comet’s structure I can explain why astronomers use models to understand celestial bodies A little bit about Comets Questions for the video: 1. What is the difference between long period and short period comets? 2. Why are some comets visible and others not? 3. Why do some comets have different tails? 4. How are the two tails formed? 5. Why do scientists think that comets may have been a cause for the extinction of dinosaurs and might have imported water to the earth? http://www.neok12.com/php/watch.php?v=zX700a 4f73526d5c7872017f&t=Comets What does Comet mean? from the Greek word komē, meaning "hair of the head“ Aristotle first used the derivation komētēs to depict comets as "stars with hair." The astronomical symbol for comets (☄) consists of a disc with a hair- like tail. Comets Comets are small, fragile, irregularly shaped bodies composed of a mixture of non-volatile grains and frozen gases. have highly elliptical orbits that bring them very close to the Sun and swing them deeply into space, often beyond the orbit of Pluto. Comet Structure Comet structures are diverse Has a surrounding cloud of diffuse material, called a coma usually grows in size and brightness as the comet approaches the Sun. Usually a small, bright nucleus (less than 10 km in diameter) is visible in the middle of the coma. The coma and the nucleus together constitute the head of the comet. Anatomy of a comet Physical Characteristics As comets approach the Sun they develop enormous tail that flow away from the Sun. When far from the Sun, the nucleus is very cold. These Comets are sometimes referred to as a "dirty snowball," since over half of their material is ice. Why are comets important? Comets may be an important part of the recipe for making planets and may be material left over from solar system formation. Some comets may have crashed into forming planets adding to their water and rock Some believe that material from comets may have brought water to Earth through impacts. How many Comets are their? The number of naked-eye comets averages to roughly one per year, though many of these are faint and unspectacular. When a historically bright or naked-eye comet is witnessed by many, it is called a “Great Comet.” Examples: Halley’s comet occurs every 75 years, last seen 1985 Comet McNaught, also known as the Great Comet of 2007 Comet Hale-Bopp seen in 1997 Where are comets found? Today, most comets are located outside our solar system in part of the original cloud of dust and gas that has remained virtually untouched for billions of years. These regions are referred to as the Oort Cloud and the Kuiper Belt. Kuiper (Pronounced Kiper)Belt The Kuiper Belt is a region of space outside the orbit of Neptune. 30 to 50 AU from the sun It contains countless comets and planetesimals. Oort Cloud The Oort cloud is the farthest from the Sun that you can go and still be in the Solar System. It is believed that most comets originate in the Oort cloud before "falling" toward the Sun. Comets with long orbital periods are not confined to the plan of the solar system. Fate of Comets Comets have a lifetime of about 10,000 years or 1,000 revolutions Eventually most of the volatile material contained in a comet nucleus evaporates away, and the comet becomes a small, dark, inert lump of rock or rubble that can resemble an asteroid. Fate of Comets Comets are also known to break up into large fragments. Some comets meet a more spectacular end – either falling into the Sun, or smashing into a planet or other body. These are called sungrazers. How scientist use models in space science Scientists make scientific questions based on current scientific theory and observation of models of phenomenon. NASA missions are designed to answer specific questions. To answer these questions, scientists start with a model which they compare with actual observations in space. As new data is gathered, the model is improved if needed and re-tested against observations Make up of your model 1 large trash bag 1/3 Liter of water to help with formation of your comet comets are made of mostly water 2/3 cup of dirt 1 teaspoon of corn starch 1 teaspoon of vinegar 1 teaspoon of alcohol 1 teaspoon of corn syrup 2 lbs of dry ice Sand and dirt take the place of interplanetary dust and silicates that are trapped in the frozen ice of comets. helps hold the comet together represents amino acids represents methanol represents organics. Organic material means anything made up of four elements carbon, hydrogen, nitrogen, and oxygen Comets are frozen gases Making a model of a comet http://www.jpl.nasa.gov/education/videos/pla yVideo.cfm?videoID=17 http://www.youtube.com/watch?v=tYc25Jt5R Sk http://cse.ssl.berkeley.edu/SegwayEd/lesson s/cometstale/frame_game.html Test Your Knowledge What is the lifespan of a comet? 10,000 years or 1,000 revolutions Test Your Knowledge What is the cloud of diffuse material surrounding a comet called? A coma Test Your Knowledge What is the average number of comets that can be seen by the naked eye every year? One a year Test Your Knowledge Why do you think that your model is a good representation of a comet? Test your knowledge Why do astronomers use models? Test Your Knowledge What is one name for a comet that is far away from the sun and has a nucleus that is in a frozen solid state? "dirty snowball" Turn in Make sure you turn in your homework, lab sheet and your constellation project. You may turn in constellation projects next class as well. Please make sure that your table is cleaned up, wiped down and all materials are returned to the roll cart. Comets should be in the orange basket in the sinks to sublimate.