3 February, 1998
Greetings from Ross Sea! Our present position aboard the Research Vessel Nathaniel B. Palmer: 74 degrees 33 minutes south latitude 179 degrees 39 minutes east longitude Today has been a little quieter. Yesterday we collected images using our side scan sonar "fish" - this is a piece of equipment that we tow behind the ship. It gives us images (made with sound) that look a little like photographs from the sea floor. Then we collected 7 cores - this was very hard work and I was very tired by the end of the day! Tomorrow we will open a few of these to photograph and sample them. We are very excited! I have been sending latitude and longitude for the past several days. What are latitude and longitude and how do they help us show where we are? You may want to look at a globe. Latitude and longitude are imaginary lines circling our globe that help us know where we are relative to any other place. Longitude lines are the circles that pass through the North Pole and the South Pole. This means that all the lines of longitude come together at the poles - so if I were to visit the South Pole, I could "run around the world" by running a circle around the Pole where all the lines come together. The "zero" line of longitude passes through Greenwich, England. There are 360 degrees of longitude around the globe, but to make it easier the globe is divided into hemispheres, or halves. You may have heard of the Northern Hemisphere (top half of the globe) or the Southern Hemisphere (bottom half of the globe). The globe also is divided into the Eastern and Western Hemispheres - each includes 180 degrees of longitude. The Eastern Hemisphere is the eastern half of the globe. We mark the longitudes from 0 degrees East to 179 degrees 59 minutes 59 seconds East. The 180 degree line divides the Eastern and Western hemispheres. On the other side of the 180 degree line is the Western Hemisphere. It extends from 179 degrees 59 minutes 59 seconds west back to 0 degrees. The 180 degree line runs right up the middle of Ross Sea, so our longitude switches from west to east and back again as we cross it! Latitude lines also circle the globe, but they form the "horizontal" circles around the globe. Lines of latitude do not come together like the lines of longitude. The Equator is a line of latitude. In fact, it is marked as the line of "zero" latitude. To the north of the Equator is the Northern Hemisphere. To the south of the Equator is the Southern Hemisphere. In which hemisphere are we working? The degrees of latitude only go as high as 90 degrees. The North Pole is at 90 degrees North. The South Pole is at 90 degrees South. The lines of latitude and longitude make a grid, with longitude lines going north to south and latitude lines going east to west. We plot our position on this grid to determine where we are. During the cruise we plot our position each hour. We also collect latitude and longitude position of the ship by computer each minute! How do we know our latitude and longitude? We use one of the most accurate systems. it has only been available to the public for about a decade. We rely on the Global Positioning System, or GPS. There are 24 satellites that make up the Global Positioning System. These satellites occupy different orbits around our Earth and constantly send out signals about where the satellite is and if it is working well. Receivers "hear" the signals and translate the signals into the distance between the satellite and the receiver (our ship). We cannot "hear" all the satellites at one time, but we only need three satellites sending information to determine our position. Why do you think we need three satellites? Each satellite gives us a signal and our receiver listens to the signal and determines the distance from the satellite. That distance could be anywhere on a circle on the globe. A second satellite helps us draw another circle. The two circles intersect in two places - we could be in either place. The third satellite helps us draw a third circle. All three circles cross at only one point - the point where we are! Our satellites and receivers are so smart, we do not have to plot all the circles. The position of our ship is calculated for us automatically. The GPS originally was put in place for the United States military efforts. However, it is now used by many people for many different purposes all over the world! This is just one example of how the technology we use in science was developed for another purpose. The techniques we use to image the sea floor also were developed for the military - to help them find submarines! Well, that's all for now. I will write more soon. Yours Truly, E. Shackleton Bear P.S. You can see more pictures at Mrs. Giesting's website at ../.Return to E. Shackleton Bear's Page
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