• No world body has designated an official day to start each new season, and different schools of thought or traditions define the seasons in different ways. In meteorology, for example, summer begins on June 1. And every school child knows that summer starts when the last school bell of the year rings. Yet today is perhaps the most widely recognized day upon which summer begins in the Northern Hemisphere and upon which winter begins on the southern half of Earth's globe.
• The fact is that Earth's orbit around the sun - and tilt on its axis - have brought us to a place in space where our world's Northern Hemisphere has its time of greatest daylight. The North

ern Hemisphere has its longest day. Meanwhile, today marks the shortest day south of the equator.
• World map courtesy of Earth and Moon Viewer. The sun is at zenith (straight overhead) the North Pacific Ocean at the instant of the 2012 June 20 solstice. In the illustration at right, Earth is rotating toward the east, or righthand, side of the photo. See how it's late afternoon in the mainland U.S. when this solstice takes place?
• Yet even as this astronomical summer begins today, throughout the world the solstice also represents a "turning" of the year. To many cultures, the solstice can mean a limit or a culmination of something. From around the world, the sun is now rising and setting as far north as it ever does. Today's solstice marks the northernmost sun. After today, the sun will begin its subtle shift southward on the sky's dome again. Thus even in summer's beginning, we find the seeds of summer's end.