Science Standards:
Nature of Science and Patterns of Change
Objectives:
Materials:
Knowing global
latitude is one of the most important variables for ocean-going vessels.
A sextant is a device that measures the altitude of almost any object,
a building, a flag pole, a tree, etc. Using simple trigonometry, the height
of an object is the determined by stepping backwards from the object until
the sextant reads 45 . Then the height of the object is the same as the
distance away from the object plus the height of the observer's eyes. Alternatively,
the height can be determined by finding the product of the tangent of the
90 minus the measured angle and the distance from the object. Used at night,
local latitude is the value as the altitude of the North Star, Polaris.
Directions:
1. Construction of the sextant. Hang a paper clip or washer
or taped penny with a 20 cm string from the center hole of a large protractor.
Tape a sighting "straw" to the straight side of the protractor and invert
as shown in the diagram below.
2. Making measurements with the sextant. Sight the tops of trees, flagpoles, or stars through the straw; the string should hang down vertically. Hold the string against the protractor and read the value. The altitude is 90 minus this measured value .
3. Determining height with sextant. Method "A" is to walk away from the object until the sextant reads 45 . The height is simply the distance from the object plus the height of the sextant. Method "B" is to sight the top of the object being measured from a known distance away. The height is simply the height of the sextant plus the product of the distance away and the tangent of the altitude.
4. Determining local latitude (conducted at night). Sight the north star, Polaris, through the straw. Again, the altitude is the measured value minus 90 . Make the measurement three times and average the results. The altitude of the Polaris is the same as your latitude. Check your results with a road map or GPS surveyor .