Make an Inclinometer & Measure your Latitude

Can you watch the rotation of the earth? Sure you can, when you periodically look at the position of the sun, moon, or stars in the sky and notice that they are changing, what you are noticing is the rotation of the planet upon which you are standing. In other words, what you are noticing is the movement of the platform you're standing on relative to these objects overhead. Cool huh?

Take a look at the picture above, it is a time exposed photo of the northern sky on a dark night. The white lines are the paths of the stars as the Earth rotates under them. You may notice that there is a fairly bright star at the center that appears to be moving only slightly. This is Polaris or the North Star and it does not appear to move much because it is located almost directly over the north pole or the Earth's axis. This simple fact makes Polaris a very useful star. To begin with, if we can find Polaris then we will always know what direction north is. Then, if you can measure Polaris' angle above the horizon, you will also know your latitude.

For this assignment you will make an instrument that you can use to measure your latitude and then you will need to teach a family member what it is used for and how to use it.

Before you can begin there is an essential skill that you will have to have; how to find Polaris. You see, most of us don't have the ability to actually see our Planet's motion relative to the stars (i.e. make a time exposed picture of the night sky in our brain) so we need to be able to find the North Star some other way. Here's how: On a clear night, locate the Big Dipper and connect an imaginary line between the two end stars in the Big Dipper. By extending this line outward away from the open part of the cup, you will find an average-looking star, the North Star.

Even though the Big Dipper changes its position during the night and during the year, the two end stars of the cup always point to the North Star. See the diagram below:

Ok, now you know how to find the North Star. Go out tonight and find it! Now it's time to make the tool you will use to measure the North Star's angle above the horizon, this tool is called an inclinometer.

Here's what you'll need:

• 1 5x8 index card
• A sharp pencil
• A compass (the math kind, not the kind for finding north)
• A ruler
• A protractor
• Scotch tape
• Thread
• A nail, washer, nut or other small object to use as a weight
• A plastic drinking straw
• A pair of scissors

Instructions for making your inclinometer will follow but please take a moment to watch the 2 brief instructional movies. They will help you understand how the inclinometer works and how to put it together. You can watch by clicking on them below.

Directions for making your inclinometer:

• Using your 5x8 index card, your pencil and a ruler, draw a line parallel to the long edge all the way across the card 3/4 of an inch from that edge. We'll call this the bottom of the card for now.
• Next, put a mark on the line 4 inches from the edge of the card, this will be at the mid-point of the line. From this center mark measure 3 3/4 inches to the left and place another mark on the line.
• Now using your compass, put the sharp point on the line at the middle mark and open it up until the pencil is on the 3 3/4 inch mark and scribe this arc until you have a nice half-circle.
• Use a protractor and your sharp pencil to put a small mark every 5 degrees starting on your line on the left hand side and working up to 90 degrees at the middle. Once you begin keep the protractor in place so you have nice even 5 degree marks.
• Now use the sharp metal point on the compass to punch a small hole at the mid-point of the line where you have previously made a mark.
• Using the ruler and a sharp pencil, connect each 5 degree mark with the hole at the mid-point, extend each line until it passes just beyond the arc. Label each line with it's corresponding degree marking starting with the first line that you drew and beginning on the far left. The first number will be 90 degrees, then 85 degrees, then 80 etc. until you get to the one directly over the mid-point mark which will be labeled 0 degrees.
• Now measure over from the left hand edge 6 inches and draw a line perpendicular to the first line you drew on the card, use your scissors and trim off the right side of the card along this line. Use the compass to scribe a second larger arc outside the your label numbers and then trim the card on this line.
• The next step will be to attach the plastic drinking straw which will act as our sighting devise. Use 2 pieces of scotch tape to attach the straw to the card along the edge just below the first line that you drew on the card. It is extremely important that the straw is parallel to this line.
• Finally, you will attach the nail (or another small weight) by tying it to the piece of thread or small string then threading it through the small hole you punched in the card and securing it on the back of the card with another piece of scotch tape.
• Your finished product should look like this: