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Avast, me hearties! The high seas be a dangerous place for pirates! We pirates weather storms, sharks, and privateers sent to sink our ships and take our loot away from us. What be even more frightenin’ than all of those, sometimes, is the danger of getting’ lost! If’n yer not in sight of land ye may lose yer way amidst an endless sea of blue. Luck be with us, though, for the mariners of old invented useful tools to help pirates and privateers alike navigate by the stars. One of ‘em is called a sextant, and today ye’ll be makin’ yer own to measure the night skies!
Materials:
- A 12-inch ruler
- A protractor
- Tape
- String
- Scissors
- A washer or a few paper clips
- Paper and pencil
Process:
- Cut a piece of string about 10-12 inches long.
- Tie the metal washer or the paper clips to one end of the string.
- Tie the other end of the string to the little hole in the middle of the flat edge of the protractor. If your protractor doesn’t have a hole, tape the string on.
- Line up the flat edge of the protractor with the edge of the ruler so that one end of the protractor is about half an inch from the end of the ruler. Tape them together. You now have a basic sextant!
- Experiment with the sextant before you use it. Hold it with the flat edge of the protractor facing up and the round edge facing down, with the string hanging straight down across the 90° line. Tilt it back and forth at different angles and notice how the string stays hanging straight down, which lets it align with different angles on the protractor.
- Take your new sextant outside on a clear night and find a bright star. You can even use the moon if you want.
- Hold the sextant up to one eye with the protractor end closest to your face. Sight up the edge of the ruler at your stellar object. While you’re holding the sextant steady, have a partner look at the string. It will be hanging down past an angle reading on the protractor. Have your partner read the angle and write it down. That is its “zenith angle,” how far away it is, in degrees, from the zenith, or the very top of the sky.
- Subtract the zenith angle from 90 to get the object’s “altitude angle,” how far away it is from the horizon.
- Try to track how your object moves over the course of a few nights! Sight it at the same time each night with your sextant and write down its zenith and altitude angles. How does it move?
Summary:
The sextant was an important tool for pirates and sailors of all kinds for centuries until more sophisticated technology like GPS was invented. It was first used in the 1700s, but the famous scientist Isaac Newton had written about the idea of a sextant in the 1600s. They used it to measure latitude, or how far north or south their ship was from the Earth’s equator. Latitude, like distance in the sky, is measured in degrees.
Alone, a can only measure the altitudes of objects in the sky. Sailors had to combine the sextant with a big book of dates, times, and the angles of various celestial objects. Often sailors would use a sextant with a darkened lens to look at the sun at noon. They would measure the sun’s altitude angle and then check their record book. The book was full of measurements taken at noon at different northern and southern latitudes every day of the year. They would find the right date and then look for the angle they measured, which would match up with a latitude measurement and help them know where the ship was on the Earth.
Your sextant doesn’t have eye protection, so make sure you never use it to look at the sun! It’s perfect for night-sky navigation, though.
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