The Introductory Lesson
TOPIC: Construct a Sextant.
SWBAT (Students will be able to) construct a sextant, understand how it works, and apply this instrument to a variety of navigational applications.
1. 1 - CD with Jewel case.
2. 5 - Lego blocks.
a. 1 - 2 x 4 brick
b. 2 - 2 x 1 plates
c. 1 - 2 x 2 brick
d. 1 - 2 x 2 plate
3. 1 - Tube of clear adhesive (Cyanoacrylate or equal).
4. 1 - Letter-size paper with back-adhesive for printing the Vernier scale on inkjet or laser printers.
5. 2 - Small mirrors (40 mm x 22 mm x 3 mm thick).
1. 1 - Ruler.
2. 1 - Scissors.
3. 1 - Paper cutter.
1. Align and adhere the circle-shaped Vernier scale to the CD.
2. Align and adhere the smaller triangle-shaped Vernier scale to the jewel case corner, adjacent to the CD.
3. Position and adhere the mirrors.
4. Position and adhere the Lego blocks.
1. Safety Warning.
Mounting mirror 1 at the center of the CD:
1. While working on a flat surface, adhere the center mirror back to the large side of a 2x4 Lego brick. The mirror should also be adhered perpendicular to the flat surface for optimum results.
2. Assemble the 2x4 Lego brick over two 2x1 Lego plates. Each 2x1 Lego plate should be positioned on opposite sides of the center hole of the CD. The 2x4 Lego brick spans the space between these Lego plates as well as the center hole of the CD.
3. Adhere the mirror assembly to the CD and adjust the following:
a. Align the large side of a 2x4 Lego brick side to the 180° scale line. The silvered surface of the mirror or the back surface of the glass mirror should be over the center hole of the CD.
b. Center the Lego plates without interfering with the center hole of the CD.
Mounting mirror 2 (half-silvered) to the CD jewel case:
I used a 2x2 Lego brick mounted on a 2x2 Lego plate, to hold the CD jewel case mirror. Cut the 4 brick bumps out, because they will be visible thru the transparent part of the half silvered mirror.
1. While working on a flat surface, adhere the half silvered mirror to the 2x2 Lego brick. Make sure the mirror is perpendicular to the flat surface.
2. Assemble the jewel case mirror brick to the plate.
3. Position and adhere the jewel case mirror assembly in the CD jewel case corner. Make sure that:
a. The CD is positioned pointing more or less as shown in the layout to the left, so you will have space to place the Vernier in the other jewel case corner afterwards.
b. Place the half silvered mirror assembly parallel to the center mirror. Position it visually.
c. The assembly should be adhered to the CD jewel case.
Adhering the Vernier scale:
At this point, your CD-Sextant is almost complete. The Vernier scale should be adhered in the 0° position:
1. Cut the Vernier in a triangular form, to fit the CD jewel case corner. I did stick the Vernier on a blank sticker paper piece, in order to make the Vernier paper ticker. This is important because the Vernier edge will be unsupported.
2. Adjust the mirrors (see fine-tuning the mirrors)
3. Rotate the CD until the mirrors are parallel.
4. While holding the instrument in position for observations look through the half silvered mirror and focus on a far away object. Turn the CD slowly until the reflected image and the direct image coincide. This must be the instrument zero, so....
5. Carefully place and stick the Vernier in the CD jewel case, reading 0°00'. This means that the Vernier tick A must coincide with the 0° scale line. On the other side of the Vernier, the 60' tick must coincide with the 59° tick in the scale.
Make sure the Vernier and CD scale are very close together. The Vernier probably will be a little higher than the CD, and you might want to bend it down a bit.