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PLAYLIST Principles for Finding Position with a Sextant

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PLAYLIST Principles for Finding Position with a Sextant PLAYLIST Principles for Finding Position with a Sextant One of our event objectives is to understand how solar geometry dictates land & sea navigation (celestial navigation). We are accomplishing this objective by watch the three required hours of video viewing needed for the Science BSA STEM Nova award. Here are the topics: - Solar Noon - Declination - Analeema Graph - Latitude / Longitude - Time Zones - Solar Geometry - International Date Line - Principal Terrestrial Latitude Circles - Sextant Basics What we're going to do afterward is use a sextant to find latitude at noon. At the same time, we're going to use watch to determine longitude. Basic Sextant Approach. The basic approach for finding position using the sextant at high (solar) noon is simple. Measure the sun angle with a sextant while keeping track of time. Use time to find longitude. Use sun angle, time, date, and declination to find latitude. Obviously, measurements are taken around solar noon, +/- 15 minutes. In fact several measurements will be made of the solar angle about 3-5 minutes apart. With each measurement, the time of measurement relative to the prime meridian is recorded. The time measurement is used several ways. First, it tells us when local solar noon occurred. This time is then converted to the observer's longitude. Finally, time is used to find the proper declination angle of the sun in look up tables. With the sextant angle and declination of the sun, latitude is determined. The purpose of these videos is to understand the concepts behind why figuring out lat/long with a sextant works. You'll also learn basic relationship about why a whole lot of things are work the way they do. To start with, it will explain the basic principles supporting GPS and finding north without a compass--a 1st Class requirement. To assist with completing the Astronomy merit badges and experiment with the content of the videos on this playlist, download and install Stelarium. http://www.stellarium.org/ Research Requirement. The BSA STEM Nova requirement for Science (Launch or Shoot) is to watch each of these videos and prepare two questions after watching each one. There is a very good possibility your questions will be answered by other videos. Nova Award Playlist Page 1 of 4 NRAO Observatory Visit: 4-7 Sep 15 The first video to watch will be "Lost at Sea, The Search for Longitude". The last video to watch is about sextant basics. Videos are ordered to help understand videos later in the sequence. Video 1. This first video is basic for understanding time and our lat/long system are tightly interrelated to each other. Over a 1000 sailing warriors died all at once for us to get a more accurate wrist watch. Lost at Sea, The Search for Longitude(53:24) https://youtu.be/HS7ZXRKOk1o Longitude gives us times zones. We will use time to find our longitude at the observatory. The key to understanding this is knowing the sun moves 15° per hour (1 minute in 4 seconds). Time zones are 15 minutes apart and set by the prime meridian. Solar noon an hour apart for each time zone, right on the 15° increment of the meridian. Please don't be confused by when our clocks tell us it's noon. It is a sloppy reality for convenience. Solar noon for your location happens when the sun is high as it is going to get each day. (Hint: Solar noon for Newnan, GA is 1346 during Daylight Savings Time--almost 2 hours later than when our clocks say it's noon) To see the relationship between solar and political (civil) time zones, have a look at this display. Newnan, GA, politically, is in the Eastern Time Zone. However, according to solar time, Newnan is over 100 miles into the Central Time Zone. It's why the sun sets so late in the summer and it's always dark when we get up. World Time Zone Map http://www.worldtimezone.com/datetime24.php The relationship of solar noon to time is shown in the World Daylight Map. The sun is always at solar noon somewhere on earth, which is why we can know our longitude position at solar noon. On this map, the solar and political time zones are shown. Notice Newnan, 084°47' W is 132 statute miles past 082°30' W--the edge of the Eastern time zone, yet we're still on Eastern time by 132 statute miles World Daylight Map http://www.timeanddate.com/worldclock/sunearth.html Video 2. After understanding longitude, we need to add latitude to our knowledge base. Contrary to what is naturally assumed, latitude is an angular measurement above or below the equator originating at the center of the earth. Yes, latitude is marked in degrees and is parallel to the equator, but is found by setting an angle at the center of the Earth and rotating Earth on its North-South Pole axis, such as with a laser beam shining from the center of Earth to the surface. The way latitude is normally presented to us is that latitude is a circular slice through the Earth, parallel to the equator. It's certainly what it looks like! However, we need to understand latitude is extended to the celestial sphere, infinitely far out in space. The key is latitude is an angular measurement from the center of Earth. Latitude & Longitude Lecture: Part 1 (30:45) Nova Award Playlist Page 2 of 4 NRAO Observatory Visit: 4-7 Sep 15 https://www.youtube.com/watch?v=9vfQM_M1Pec Video 3. To find latitude with a sextant, solar declination needs to be understood. This video highlights basic principles in easy-to-understand terms. Solar Orientation (10:50) https://www.youtube.com/watch?v=OR8EQ0DWpPw Video 4. When finding latitude with a sextant, a more precise definition of what the declination is at the time the measurement is taken is needed. The Earth Sun Geometry video brings us closer to understanding how this information is presented and used for use with The Nautical Almanac to find latitude. Though the sun doesn't move, it appears to move because Earth is spinning with a tilted N-S axis on an elliptical orbit. This relationship is shown with an Analeema Graph. This shown by running the Analeema script in Stellarium. In fact, the Nautical Almanac presents the Analeema graph in tabular form. Declination also explains why the sun will always be south of Newnan, GA and never overhead. Before watching this video, it's important to know what the principal terrestrial latitude circles are. They include the equator, Tropic of Cancer/Capricorn, and Arctic/Antarctic Circle . Note, these principal circles are defined by the lowest and high points at the solstices and equinoxes. See . Major Circles of Latitude https://en.wikipedia.org/wiki/Circle_of_latitude#Major_circles_of_latitude Videos 5 & 6. To introduce the behavior of Earth's tilt and its effects on seasons is this video. It explains how the noon day sun creates seasons. The goal is to understand why the sun is lower in the sky from our position in Newnan, GA in winter than where it is during summer. It discusses why daylight and temperature are different throughout the year. Seasons - What Causes the Seasons (10:48) https://www.youtube.com/watch?v=rcquRMaVSKU After reading this section about Circles of Latitude, watch this animation to understand the summary of the relationship of declination to seasons. Mechanism of Seasons (5: 59) https://www.youtube.com/watch?v=WLRA87TKXLM Video 7. Videos 4-6 make it easier to understand a more precise definition of declination. Earth Sun Geometry (16.29) https://www.youtube.com/watch?v=rnM1hXJf4WU Stop watching this next video, if desired, at 13.00 minutes. Video 8. After exploring declination, then it's a lot easier to understand the continuation of the lecture we started earlier. In this video, the International Date Line is added to the discussion. Nova Award Playlist Page 3 of 4 NRAO Observatory Visit: 4-7 Sep 15 Knowing what day is it where the sun is important to be able to look up declination data for use with the sextant. Beware. The lecturer is not talking with children, so, at times (but not often) language is coarse. Latitude & Longitude Lecture: Part 2 (28:30) https://www.youtube.com/watch?v=OXuc84bP90k Video 9. At the National Radio Astronomy Observatory, we will show how all this information works together to help us use a sextant for finding observer lat/long position--some a GPS does for us. Just remember these concepts studied here are fundamental for how our a GPS system works. Sextant Basics (7:51) https://www.youtube.com/watch?v=DrAkrgZRb9Y Milepost Achieved. After completing this sequence of videos, it will be a lot easier to understand how our explanation of how our position at the observatory is found at the observatory. When we're done with this lecture, you'll always be able to find your precise longitude, regardless of whether you're on land or sea. Find precise latitude requires a water horizon, but you can get close, not matter where you are. Nova Award Playlist Page 4 of 4 NRAO Observatory Visit: 4-7 Sep 15 .
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