Tomorrow is the winter solstice for my location in North America, and then the Sun can begin its northward journey along the horizon and the days can lengthen again. For “Everything you need to know: winter solstice 2012,” see this guide on EarthSky.
In honor of the solstice, Bedtime Math has a solstice- and shadow-related math problem for your little ones tonight. The intro text talks about a sundial clock and how to make a simple version of one.
Since it’s the solstice tomorrow, I want to suggest you consider starting a meridian calendar, especially if you have a large yard with space in the north and a tall utility pole in the yard that you want to make even more useful. For this calendar, you mark the location of the top of the pole’s shadow at local apparent noon with, say, a large boulder, on the solstices and equinoxes. It becomes a neat visual representation of how the angle of the Sun’s rays vary with and cause the seasons, due to the Earth’s tilt on its axis. The example in the photo comes from Valley City, North Dakota, at the Medicine Wheel Park. The Medicine Wheel is another solar calendar which marks the sunrise and sunset positions along the horizon for the equinoxes and solstices–another neat visual representation of the seasonal change in the Sun’s light on Earth.