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People often say that the sun rises in the east. That’s not exactly true. If you watch the sun rise each morning over the course of an entire year, you’ll see that the sun doesn’t always rise in the same place.

See how the sun moves across the horizon through the year. Watch | Get Flash plug-in

In the summer, the sun rises somewhat north of due east. The date on which it rises the farthest to the north is roughly June 21, the summer solstice and the longest day of the year in the Northern Hemisphere.

In the winter, the sun rises somewhat south of due east. The date on which it rises the farthest to the south is around December 21, the winter solstice, the shortest day of the year in the Northern Hemisphere.

The changing location of the sunrise is easy to track on an unobstructed horizon. In March and September, the change is fast—the sun moves a full solar diameter each day. At the solstices, the change is slow, so slow that the sun seems to stop. (Solstice is Latin for "standstill.")

Why does the sun’s path across the sky change throughout the year? The reason is that the earth is tilted—by 23.5 degrees, to be exact—with respect to its orbit.

See how the area of the globe in sunlight changes through the year. Watch | Get Flash plug-in

When it’s summer in the Northern hemisphere, the North Pole is tilted toward the sun and the sun shines on a greater area of the Northern Hemisphere. As the earth spins, places in the Northern Hemisphere stay in the sunlit area longer, and that means the days are longer.

When it’s winter in the Northern Hemisphere, the North Pole is tilted away from the sun, the sun shines on a smaller area of the Northern Hemisphere, and the days are shorter.

At two points in the earth’s orbit around the sun, the earth is pointed neither toward nor away from the sun. These two points are called the equinoxes, which fall on roughly March 21 and September 23. On these two days, there are equal amounts of daytime and nighttime—twelve hours each—everywhere on earth.

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