Determining the Winter Solstice Tibetan Style
According to the Kalacakravatara, the winter solstice is observational determined through the use of shadows as follows:
On level ground in the middle of a circle of one cubit diameter, plant a stick in the ground that measures the length from the tip of your thumb to the tip of your middle finger. The line of the stick's morning shadow gradually shortens from outside the mandala. When it reaches the edge of the mandala, at that time and in that place, make the mark of the crowfoot [an X]. That is west. In the afternoon the shadow gradually lengthens from the center of the mandala. Repeat the process as before, and the mark will indicate east. Anchoring thread at one of the marks, and beginning directly in front of the other mark, draw a circle with chalk. Anchor thread at the other mark and do the same, thereby creating the shape of a fish. In the middle of the two circles, the center of the mouth of the fish is the south, and the center of the tail is the north. Having ascertained the directions rub out the circles. Starting from the tenth day before the sun makes its northward journey, make observations at midday. When the shadow begins to move inside from outside the northern edge of the original circle, that is the day the sun changes to its northward journey. [Ornament of Stainless Light, pg 127]
Since we have access to compasses, we can ascertain north and south much more easily, and therefore duplicate the observation of the midday shadow with students as young as elementary school. In simple English, draw a circle on the ground and plant a gnomon stick in the center. Beginning some days before the winter solstice, mark the length of the midday shadow relative to the circle. Repeat on each sunny day. When the shadow stops lengthening and begins to shorten, you've found the winter solstice. Note that the opposite experiment can be done at the summer solstice. Note that this version of determining the winter solstice is easier than measuring the most southward sunrise along the horizon (the method used at Stonehenge, for example), and can be done at an hour when children are more likely to be in school. This is also a natural cultural extension of the Astronomy with a Stick lesson plans.