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Earth Sense: Solstice marks longest day, shortest night of year
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Summer starts a few days from now.

June 21 will be the longest day and the shortest night of the year in the continental U.S. and the rest of the Northern Hemisphere.

Online diagrams explaining how it works can look confusing. A comment by a reader confirmed this with the question: “Why do they keep changing it, instead of having sunset at the same time each day?”

No government in the world has the power to freeze sunrise and sunset times, and especially not the seasons. The time of day is controlled by the Earth’s rotation around its own axis.

The part that’s in the “shade,” facing away from the sun, has nighttime. The other half is in the daylight.

Many governments try to fit daytime hours into this by adjusting the clock, as we do with daylight saving time. The results are questionable, given the fact there are clocks built into so many appliances now, some self-adjusting and some not. This forces people to hunt down every wristwatch, alarm clock, radio and whatever to set the correct time twice a year. 

Seasons are controlled neither by the Earth’s rotation, nor by distance from the sun. They are produced by the globe’s axis tilt.

Once a year, the North Pole is inclined toward the sun. That’s happening this week.

If you imagine the Earth to be your head, you’d be “nodding,” and the sun would shine most directly on your forehead.

Twice a year (in March and September), the tilt of the axis places us sideways, so our left or right cheek would be illuminated. Those are the equinoxes.

The beginning of winter occurs Dec. 21, when the “head” is tilted backward, illuminating the chin.

In this analogy, North America, Europe and Asia would be the forehead, receiving the most sunlight in June. The chin includes South America, southern Africa, Australia, and anything else south of the equator. 

Right now, because our Northern Hemisphere is tilted toward the sun, much of it is in the daylight. Only a small section at a time experiences darkness, and rotates out of it quickly. That explains the late sunset and early sunrise times. Because the “chin” in our analogy is tilted way down, the Southern Hemisphere seasons are the opposite of ours. So Chile, Argentina, Australia and others start their winter this week.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at