Astlcc1 - Laboratory 1 Celestial Coordinates I Materials Used ESSCO SC001 Constellation Star Chart Edmund Scientific Star and Planet

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1 Laboratory 1 - Celestial Coordinates I Materials Used: ESSCO ® SC001 Constellation Star Chart, Edmund Scientific Star and Planet Locator (Planisphere) and user manual. Objectives: To become acquainted with basic navigation of the night sky; to become familiar with planispheres and star charts and to use them to locate objects in the night sky. Discussion: Astronomers and other observers need to navigate the sky quickly in order to locate objects of interest. A traditional method of doing this is to identify prominent groups of stars known as asterisms or constellations that are patterns of stars that resemble familiar objects. An early astronomer might have given directions to something of interest in the sky, the Trapezium star cluster for instance, by referring to its location in the belt of the constellation Orion (the hunter). While this works well for locating objects that can be seen with the unaided eye, deep sky objects (those too faint to be seen without a telescope) require a more exacting system of location. From our observing position on Earth the night sky appears as if it were superimposed on the inside of a large bowl surrounding us known as the celestial sphere. A system of coordinates superimposed on the surface of this sphere is used for locating objects in the sky that is analogous to the well-known system of latitude and longitude is used to locate positions on the earth. If we wish to specify the location of something on the surface of the earth, Pocatello or Idaho Falls for instance, we do so using a grid formed by lines of latitude and longitude - in this case 42 0 52’ N, 112 0 27’ W for Pocatello and 43 0 29’ N, 112 0 02’ W for Idaho Falls. Latitude is the angular distance north or south of the equator in degrees, minutes and seconds ranging from 0 0 to ± 90 0 . Lines of latitude are known as parallels , each being parallel to the equator. Longitude is the angular distance east or west of the prime meridian (which runs through Greenwich, England) in degrees, minutes and seconds ranging from 0 0 to ± 180 0 . Lines of longitude are known as meridians . All meridians pass through both poles. Meridians are great arcs since they slice the earth along a plane that goes through its center. Great arcs are of interest in navigating any long distance across the earth since the shortest path across the surface of a sphere is a great arc rather than a straight line (this is why airlines fly routes along great arcs). Latitude and longitude rotate with the earth so these coordinates to not change with time of day, year, etc. A system similar to latitude and longitude is used to locate positions in the night sky. Like latitude and longitude, declination and right ascension rotate with the sky and uniquely locate an object’s position in the sky. But unlike latitude and longitude, declination and right ascension drift (slowly) due to the precessional motion of the earth. Maps of the sky must be periodically updated to keep up with this drift. Notice that there is an assumption inherent in both systems of location that all objects are
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This note was uploaded on 01/16/2012 for the course PHYS 153 taught by Professor Hackwrth,m during the Spring '08 term at Idaho State University.

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Astlcc1 - Laboratory 1 Celestial Coordinates I Materials Used ESSCO SC001 Constellation Star Chart Edmund Scientific Star and Planet

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