What is the summer solstice?

Meteorologist Sarah Spivey explains science of year's longest day

SAN ANTONIO – We all know that it feels like summer in San Antonio from the end of May through early October. However, the hottest season of the year officially kicks off June 21 at 10:54 a.m. with the summer solstice.


You may remember learning in grade school that the Earth spins on an axis, making one rotation every 24 hours -- that's a day. If all things stayed the same, every point on the Earth from the equator to the poles would experience 12 hours of daylight and 12 hours of night. There would be no seasons, and the weather would not vary too much day-to-day.

However, because the Earth is tilted at a 23.5-degree angle, seasons can exist. Summer is experienced when the axis is tilted toward the sun, and winter happens when the axis is tilted away from the sun.

Amount of daylight varies, too. During the warm season, the sun never sets at the poles. And during the cold season, there are 24 hours of darkness. That means that the closer you are to the poles, the more daylight you experience during the summer months.


The longest day of the year occurs on the summer solstice. In the Northern Hemisphere this year, that's on June 21 at 10:54 am CST when the angle of the sun is directly over the Tropic of Cancer.


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