Monday, February 18, 2013

Projects with sundials

Projects with sundials

It's interesting:
"Today, I think we have all learned that there are few things more marvellous than an Autumn wedding, and nothing more beautiful than a Fall bride. It is wonderful occasions like this that provide us all with great memories that we will never, ever forget, and I am incredibly honoured to have been of part of this special day. Also, I want to thank you for getting married at this time of the year, because now, whenever I see the leaves turning colour and falling off the trees, I’ll be reminded that it’s time to buy your anniversary gift."

Sundials use the position of the sun to measure the time of day. Iconic models use a thin rod or triangle, called a style or gnomon, to cast a shadow and indicate the time, but other sundials use a line of light, which can be let in through a small hole, focused through a lens or reflected by a mirror. For an interesting project, try making, adjusting and reading different sundials.

  1. Equatorial Sundial

    • Collect a protractor, drinking straw or knitting needle and a piece of thick paper or thin cardboard about 25 cm long, and a little wider than your protractor. Draw a line 1 cm from each end across the paper- label them lines A and C. If you live above 50 degrees latitude, draw another line 15 cm from the back end- if you live below 50 degrees, make it 16 or 17 cm. This is line B. Draw a dot on the mid-point of each line, and draw a line down the middle connecting them. Center your protractor on the midpoint of line A and trace around it, then mark off 15-degree intervals. Make a pinhole at the midpoint and repeat this on the back of the paper in the same spot. Fold the paper perpendicularly at line B, then fold the ends of the paper in toward that fold at lines A and C. Push a straw through the hole you made at the midpoint of A, and set the straw at a right angle to the paper. Lean the straw and paper back toward the other end of the paper (line C) until the fold at line B makes the same angle as your latitude in degrees. Secure the straw in place by cutting a tab in the flap at line C and inserting it into the straw. You can now align your gnomon with the earth's north pole and read the sun time.

    Horizontal Sundial

    • Select a sturdy rectangular base, such as a piece of wood or cardboard. Draw a stencil for your triangular gnomon. Label the point at the center of the sundial as A, the top point B and the back point C. Line AC is the longest- it rests on the base. Angles A and C should be equivalent to your latitude. Use this stencil to cut out a gnomon from a sturdy material, such as wood or cardboard. Also cut out a cylindrical rod a little bit longer than side BC of your triangle. Glue side AC of your gnomon to the middle back of your base, and glue the rod to side BC. Fold a piece of paper in half, and set a protractor in the middle along the top edge. Trace around the protractor and mark off every 15 degrees. Set the piece of paper against side AB of the triangle, right under the protruding rod. Tie a long piece of string to the rod, and set a piece of paper under the sundial that is several inches wider than the base. Mark the points where the 15-degree lines touch the base of the sundial, and use the string to follow the lines that extend beyond the base and mark their contact points on the piece of paper underneath. Remove the paper below the rod, and use a ruler to trace lines from point C through each of the points you just made, marking the 15 degree lines. These are the hour lines. Use a compass to orient the base on the north/south axis.

    Orienting Sundials

    • There are three ways you can orient a sundial. The easiest and most practical way is to use a compass and align the sundial gnomon on the north/south axis. A lazier, but less effective way, is to look at the time on an electric clock and adjust the sundial so it reads the same time. If you want to be a purist, though, you can orient your sundial without any mechanical objects by pointing your sundial at the North Star at night. The North Star, or Polaris, is within one degree of the North Pole, which is the true object towards which the sundial should be pointed. This method only works for inhabitants of the Northern Hemisphere. If you are working on sundials in class, challenge your students to come up with their own methods for orienting sundials.

    Unusual Sundials

    • There are many sundials besides equatorial and horizontal models. You can download a pattern for an equiangular sundial, which requires no knowledge of your latitude or the north/south axis, or you can follow the intricate angular patterns for a portable Capuchin sundial, which uses a hanging thread and a complex pattern of curves and squares to give the time based on the date. Vertical sundials are similar to their horizontal counterparts, but the plane is aligned vertically, and spherical sundials use a sphere-shaped plane, rather than a flat base. Of course, the simplest sundial is just a stick stuck in the ground- these gave rise to the famous Egyptian obelisks. You can experiment with different types of sundials and research which models are the easiest to make, the most accurate or the most beneficial for your latitude.


Tags: piece paper, your latitude, north south, north south axis, south axis