Each year, sometime between January 1 and 4, planet Earth reaches its closest approach to the sun. At this moment, called perihelion, it is 3.1 million miles closer to the sun than on or near July 4 when the Earth-sun distance is 94.5 million miles (the latter moment is called aphelion). This happens because our planet’s orbit is not perfectly round but elliptical. Astronomers tell us that tomorrow, on January 4, 2014, at 5:59 a.m. CST, the earth will be only 91,406,671 miles from the sun.
So Minnesota is closest to the sun in January, but it is nevertheless our coldest month of the year. During January in the Northern Hemisphere, the sun remains low in the sky. Days are warmer in the spring, summer and fall in Minnesota when the sun is higher in the sky, concentrating more heat on each acre of land or water. Also, we have more daylight hours the rest of the year, giving the sun more time to heat the land and water, which then heat the atmosphere.
We have gained 7 minutes of daylight since the winter solstice on December 21, but things typically continue to get colder for another 3 weeks, with our coldest days often arriving in late January. It takes that long before radiation from the slowly returning amount of daylight can have a positive effect on the frozen snow-covered ground and chilly air. Statistically, January 25 is our coldest day of the year.
Jim Gilbert’s Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.