Today, 21 June, at 10:24, summer began astronomically - the longest day of the year, when the day here lasts 15 hours and 14 minutes. From tomorrow, imperceptibly, the light begins to shorten, even though the heat is only now truly arriving.

Behind the date stands pure astronomy, not the calendar. The seasons don't change according to the pages of the calendar, but according to the Earth's motion around the Sun. Because of the tilt of the Earth's axis of about 23.5 degrees, the northern hemisphere right now receives the maximum of direct sunlight, and the Sun reaches its northernmost point in the sky.

The irony of the summer solstice is that just when the day is longest, it already begins to shrink. The hottest days, meanwhile, usually come later - in July and August. Nature has its own tempo that doesn't much care how we count the days.

For us in the Balkans, where summer means the beach and blocked border crossings and electricity bills that climb with every air conditioner switched on, the start of summer is more than an astronomical trifle. It's the beginning of a season in which everything - from tourism to the temperature in the bedroom - becomes harder to ignore.