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Me and My Shadow - Making the Sun-Earth Connection

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Me and My Shadow - Making the Sun-Earth Connection I have a little shadow that Sandburg Center for Sky Awareness goes in and out with me, A Fairfax County Public Schools Planetarium And what can be the use of him is more than I can see.... Me and My Shadow - My Shadow, Robert Louis Stevenson Making the Sun-Earth Connection Me and My Shadow On a sunny day, drive a stake into the ground and observe how its shadow - Mills Brothers changes throughout the day or year--a simple yet profound way to demonstrate the interconnection between the Sun and Earth! The following Web resources may help you to more fully comprehend the deeper meaning of these simple observations. The Analemma Ever notice the odd-looking figure eight that appears on many globes? It's called an analemma. Visit the Analemma Web site to learn more Use a sundial to measure about, well, analemmas, including an explanation of how the analemma Solar Time. Get the current is derived from the stake you drove into the ground. Standard Time from The Official U.S. Time Web See Dennis di Cicco's award-winning time lapse photograph of the Sun page. (showing the analemma). See also Building an Analemma Curve, courtesy the Analemma Society. Construct an indoor analemma; Most days, Solar Time is slightly different from construct an outdoor analemma. Calculate & chart an analemma for any Standard Time (up to 16 location at any time of day. min. fast or 14 min. slow). This time difference is A graph of the analemma for Washington, D.C. shows the Equation of known as the Equation of Time (Offset of the Sun) corrected for the eight-minute solar time Time. difference between Washington, D.C. (77°W) and 75°W--the Standard Time Meridian for the Eastern Time Zone. Can you tell when the Are You maximum & minimum altitude of the midday Sun occurs during the Clock-wise? year? Ever wonder why is Close examination of an almanac reveals that the latest sunrise and Clockwise clockwise? As it earliest sunset do not occur--as one would expect--on the December turns out, for objects in the Solstice (on average, 21 DEC), the day with the fewest hours of daylight Northern Hemisphere, in the Northern Hemisphere. As it turns out, the earliest sunsets occur in shadows cast by the Sun move in a clockwise early December and the latest sunrises occur in early January. [A similar direction. In fact, the word situation occurs before/after the June Solstice (on average, 21 JUN).] A hour means "the day" or puzzling mystery easily solved by the analemma! For details, see Why "Sun's path." For details, the earliest sunset, latest sunrise, and shortest day of the year occur on see the How Sundials Work different dates. Web page. Every day, Sun Calculators shadows... Explore the daily and annual cycles of change in the apparent path of the Sun across the sky. Great Circle Studio's Solar Calculator will calculate ...are shortest at noon, and the Sun's altitude and azimuth for a user-specified location, date & time, longest at sunrise & sunset. On June 21, noon shadows and data interval. A variety of output modes are available. Use this http://www.wsanford.com/~wsanford/exo/sundials/shadows.html (1 of 9) [3/2/2004 9:26:26 PM] Me and My Shadow - Making the Sun-Earth Connection are the shortest of any day information to predict how the length of your shadow would change daily during the year (for northern and annually (at the same time each day). Verify your predictions using mid-latitude locations), and the SCSA Shadow Length Calculator. vice-versa on December 21 (see solstice/equinox How can you determine the height of objects too tall to measure directly? diagram). Using shadows, of course! Use the SCSA Object Height Calculator to Due to the geometry of calculate the height of tall shadow-casters, e.g., buildings, flagpoles, equatorial sundials, the utility poles, trees, etc. gnomon shadow is the same length for the entire Using user-specified times of sunrise and sunset, the SCSA Daylight day (although its length Calculator calculates the number of hours of daylight, also known as the varies from day-to-day according to the annual Duration of Insolation (Incoming Solar Radiation). cycle of change in the declination of the Sun). The Solar Noon Calendar calculates tables showing either the exact time of Solar Noon for your location for each day of the year, or the Longitude is... Standard Time Correction (the amount you have to add to, or to subtract from, solar time on your sundial to get the time shown on your wristwatch). ...equivalent to time, and vice versa. If you know the The NASA J-Track Web page shows where on Earth the Sun is currently time difference between two locations, then you can use directly overhead (see small Sun icon, correctly oriented with respect to the rate of the Earth's latitude and longitude). rotation (15°/hr or 1°/4 min) to calculate the difference in longitude between the two You Can Make a Sundial! places. Tell time using shadows! As its name suggests, the You Can Make a For example, Solar Noon Sundial! Web site generates sundials for a user-specified location. occurs eight minutes later in Washington, D.C. than it Several types of sundials are available in a variety of output formats does on the Standard Time (GIF, PDF, and EPS). Start by making a customized horizontal sundial Meridian for the Eastern similar to the "Sandburg Sundial," a ready-to-use horizontal sundial Time Zone (75°W); how available for downloading in two file formats (some assembly required): many degrees of longitude separate the two locations? ● Lower Resolution - dial.gif (16k) plus gnomon.gif (7k) ● 8 min x 1°/4 min = 2° Higher Resolution - sandburg_sundial.pdf (54k) [Download free Adobe Acrobat Reader.] Therefore, the longitude of Washington, D.C. is 77°W. ● Enhanced Sandburg Sundial (29k) - featuring arcs showing Simple, huh? Well, it wasn't apparent solar altitude from 10-70 degrees above the horizon, always so easy! Read The courtesy sundialist Robert "Shadow Master" Hough [Note: The Illustrated Longitude, the story of clockmaker John "dot" that appears along the upper edge of the gnomon (technically Harrison, who solved the known as the style) is called the nodus. Determine the solar problem that Newton and altitude by observing where the nodus shadow falls among the arcs Galileo failed to on the dial face (mnemonic: notice the nodus).] conquer--how to determine longitude at sea. See also, Print sundial templates using cover stock. For directions regarding set-up Lost at Sea--the Search for and use, visit the How to Set Up & Use a Horizontal Sundial Web page. Longitude from PBS/NOVA For reference, visit the North American Sundial Society Horizontal Online. Sundial Glossary. Long story short, sundials must be corrected for Experiment with several other interesting types of sundials (designed for longitude (as well as the 39°N latitude): Equation of Time) so that ● Combination Analemmatic-Horizontal Sundial - Unlike other types http://www.wsanford.com/~wsanford/exo/sundials/shadows.html (2 of 9) [3/2/2004 9:26:26 PM] Me and My Shadow - Making the Sun-Earth Connection Solar Time reads the same of sundials that must be carefully oriented before they will work as Standard Time. properly, the combination analemmatic-horizontal sundial is self-orienting. How it works: Assemble the horizontal sundial Did You Know... (lower dial). Place the combination sundial on a horizontal surface. Using the analemmatic sundial (upper dial), stick a vertical pin in ...that Earth is eight today's date along the date scale (vertical line, center of dial). light-minutes from the Sun? [Note that pin placement is more precise on the first day of each Huh? That's right. At the month (and the equinoxes).] Keep the paper horizontal and turn it speed of light (186,000 miles per second, or until the two sundials display the same time--both sundials are now 300,000 km/sec), it takes properly oriented and the compass rose indicates true direction. nearly eight minutes for That's cool--a combination sundial-Sun compass! Why it works: sunlight to reach the Earth. The analemmatic sundial measures time with respect to the The Earth is connected to the Sun, but it is a azimuth of the Sun; the horizontal sundial measures time with long-distance connection! respect to the distance of the Sun from the meridian. 30 JUL 2002 ● Analemmatic Sundial - A relatively uncommon type of sundial (derived from the equatorial sundial), the analemmatic sundial features a gnomon that moves throughout the year. See the Analemmatic Sundials Web page for numerous examples of analemmatic sundials located around the world. ● Equatorial Sundial (assembly instructions) - The foundation of all gnomonics, the art and science of sundials. From an educator's point of view, the equatorial sundial is by far the best type of sundial for teaching a wide range of fundamental concepts in astronomy, geography, and mathematics. See the SCSA Today's sunspot Educator's Guide to Equatorial Sundials for background number is information and suggested teaching strategies. 304 / You Can Construct a Sundial! Sunspot No. Trend (past 24 hours) The preceding section features a variety of ready-made, / Increasing ready-to-assemble sundials--little if any prerequisite knowledge is -- Steady necessary to begin sundialing. Sooner or later, you'll want to know what \ Decreasing makes a sundial tick (pun intended)--at that point in time, you are ready to construct a sundial from scratch.
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