Summer arrives on the first day of June, at least according to meteorologists, who remind us that this day marks the beginning of what is historically the warmest 92 days of the year. Astronomers have us waiting until June 21 for summer to begin, when the Earth’s orbit is positioned so that the north polar end of its axis leans at the full 23 ½-degree angle toward the sun, providing constant daylight to all parts of the Earth north of the Arctic Circle. The Northern Hemisphere’s longest span of daylight takes place on our summer solstice. Nights will slowly lengthen and days diminish until December’s winter solstice.
Astronomical summer begins this year on June 21 at 5:51 a.m. CDT. It is our longest day of the year with 15 hours and 36 minutes of sunlight in the Twin Cities area. Winona, in southeastern Minnesota, will have 15 hours and 30 minutes of sunlight, and Hallock, in the extreme northwestern part of the state, will have 16 hours and 15 minutes of sunlight. If we don’t count seconds, we in the Twin Cities area actually have 15 hours and 36 minutes from June 17 through June 24. One minute will be lost on June 25.
Even though the sun is highest in the sky right now (68 ½ degrees above the horizon at noon) it will take about five more weeks until we get our warmest days. July 26 is statistically our warmest day of the year. This is due to the lag it takes to heat the Earth’s surface, for it is the radiation given off by the Earth that heats its atmosphere.
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.