Paper Plate Education Video Excerpts: Latitude by PolarisThe following pictures and narration are excerpted from the Paper Plate Astronomy video. Here we will show how a navigator determines her latitude from the altitude of Polaris, the North Star. As our navigator’s ship travels from the equator... ...the altitude of Polaris above her horizon not only increases, but is congruent with her latitude. By the time she reaches 90 degrees of latitude... ...the altitude of Polaris is likewise 90 degrees. Draw a circle to represent the earth on 10inch white plate. Extend the equator out to the edge, and extend the north pole out to the edge, too. Label these the equator, celestial equator or C.E. , north, and Polaris at the north celestial pole. Polaris is so far away that its starlight is coming in parallel to the north celestial pole. Draw several parallel lines to reinforce this notion. Looking up any one of these lines of sight, no matter where you are on the earth will end on the north star. Use a protractor and label the latitude, shown here in increments of 15 degrees. From about this part of the earth...to about here, cut a slit along the perimeter of the earth. Mark a 3 by 5 card as shown... Draw some water with a ship on it... [This is the direction our navigator would look toward the horizon, so ] label the red arrow “To Horizon”. This the direction to our navigator’s horizon, up from which she measures the altitude of the stars. Slip the card under the slit on the plate so the waterline is on the edge of the earth. With the vertical line visible at the earth’s center, mark the card. Cut out around the ship and punch out the two holes, as shown. On a second 3 by 5 card, draw a red arrow and label it North. Swing an arc...punch a hole... and cut it out as shown. Fasten the arrow cutout to the ship cutout at the 90 degree bend. And then affix the hole rig to the plate. Using the Latitude
by Polaris If our ship begins a journey north at the equator, the navigator looks this way to see starlight from Polaris coming in tangent to the equator. From the perspective of the ship, the direction the North Star is straight ahead toward the northern horizon. The altitude of Polaris is zero degrees. ...the angle between the horizon and Polaris, the altitude, is 30 degrees... At the same time, the angle from the equator to the ship’s position, the latitude, is also 30 degrees. The ship moves north. When the altitude of Polaris is 45 degrees, the ship’s latitude... By the time the ship reaches the north pole, the pole star is directly overhead altitude equals 90 degrees... At the pole, the latitude is 90 degrees. For a different perspective you can focus in on the ship to see the angular height of Polaris rising congruent with angle of latitude.

Copyright ©2012 Chuck Bueter. All rights reserved. 