This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Most kids learn in elementary school that the seasons are caused by Earth rotating on a tilted axis during its yearly orbit around the sun. The substantial tilt, about 23.5 degrees, is thought to be the result of an ancient planetary body, Theia, smashing into Earth about 4.5 billion years ago, in the same cataclysmic collision that formed the moon.
To visualize why Earth has seasons, imagine the planet as a spinning top tilted to one side. Around the June solstice, the Northern Hemisphere leans toward the sun, bringing more direct sunlight and longer days. Around the December solstice, the Southern Hemisphere does the same.
That's why June ushers in summer and warm weather in the Northern Hemisphere, while December does so in the Southern Hemisphere. The March and September equinoxes serve as the midpoints between these two seasonal extremes. On those days, the terminator—the boundary between the sunlit and dark sides of Earth—runs directly through both poles.
As a result, the Northern and Southern hemispheres receive almost the same amount of sunlight, and day and night are nearly equal in length. What do the seasons look like from about one million miles away? That's the view provided by NASA's EPIC (Earth Polychromatic Imaging Camera) aboard NOAA's DSCOVR (Deep Space Climate Observatory) mission.
By maintaining an orbit that puts the spacecraft between the sun and Earth roughly 1.6 million kilometers (1 million miles) from Earth, the camera has a nearly continuous view of the sunlit hemisphere. As Earth spins during the course of a day, EPIC captures a full-disk image of the planet's sunlit face every few hours. The four images above, taken at roughly the same time of day, show how EPIC's view of the Western Hemisphere changes over the year, from the December solstice (upper left) to the March equinox (upper right), June solstice (lower left), and September equinox (lower right).
The most striking difference is between the two solstices. In December, South America lies near the center of the disk and much of Antarctica is visible, while North America is partially out of view. In June, Earth's tilt means the situation is reversed: The Northern Hemisphere and North America are more centered, Arctic sea ice comes into view, South America is offset, and Antarctica is completely out of view.
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