Usually, the coldest time of the year is later than the winter solstice, in January and February. Laboratory hands-on investigation of heat capacity. Students have three flasks, each with a thermometer inserted through a hole in the stopper. Students expose all three flasks to a heat source, for example an electric space heater. At regular intervals, students observe, record and plot on a graph, the temperature of each flask.
Teacher asks students when is longest day of year and shortest day of year.
Students examine data showing solar radiation input over the course of one or more years. Students note that solar radiation input has maximum around longest day of year, and minimum around shortest day of year. Teacher asks students when is coldest time of year. It takes more energy input to warm up soil or water by a given amount than it does to warm up air by the same amount. Contact with still-cool soil and water keeps the air cooler than it would otherwise have been in the spring.