A couple of months ago I started a new series on this blog titled "What Is". Thus far the focus is on the field of astronomy where we hear all sorts of cool science taking place in space. The goal of this series is to explain the details of different objects we hear about relatively frequently.
What is the Summer Solstice?
The summer solstice, the first day of summer, was on June 21 this year (2019). What does this mean? The summer solstice is defined as the day (there's an exact time too, but let's not worry about that detail) when the Sun is at its highest point in the sky as observed from the northern hemisphere and the day on which the Sun's rays are most direct in the northern hemisphere. On this day the Sun was directly above the Tropic of Cancer at about 23.5 degrees north latitude. If you were standing anywhere on the Tropic of Cancer, the Sun would be directly above you at the middle point of the day.
What causes this? The reason we have the summer/winter solstice, and the spring/fall equinox, is due to Earth's tilt of about 23.5 degrees. Because Earth is titled with an axis always pointing in the same direction, the angle the Sun's light hits the Earth changes.
If Earth was not tilted, we wouldn't have seasons! But it is and we have the change of seasons! On June 21st this year, the Sun's rays were most direct, meaning a square foot of Earth in the northern hemisphere, received more energy than at any other time of the year, ignoring the effects of clouds an local weather. If that's the case, why is June not the hottest month of the year? The reason is simple. It takes time for the ground and air to warm up following winter and spring. Even though the Sun is not as direct and not as high in the sky in July and August, those months are typically hotter than June!
The summer solstice is not always June 21. It varies by a day or so each way depending on the exact time the Sun is most direct and highest in the sky. Today is June 24th, three days after the summer solstice. From each day here on out until December 21, the Sun will slowly drop a bit in the sky each day until it is at its lowest point in the sky on the winter solstice. Don't worry though, I'm sure there are plenty of beach and swimming pool days left this summer!
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