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Animation showing the tilt of the Earth's axis.The Tilt of Earth's Axis
The second orbital change Milankovich studied is the tilt of Earth's axis relative to its orbit around the Sun. The tilt of Earth's axis is the main cause of the seasons. If Earth had no tilt, then the length of daylight and the intensity of solar heating seen by a person standing at a single place on the surface would be the same all year round. The area near Earth's equator would still be hotter than the area around the poles, but there would be no seasonal changes in temperature: the Equator would always be hot, the poles would always be cold, and the US would always be blah!

Image showing the Earth at two different times in one year.  The first, the Northern hemisphere is pointed more directly towards the Sun. The second, six months later, it is pointed more away from the Sun.  Please have someone assist you with this.

But Earth does have a tilt, so on one side of the orbit, the Northern hemisphere is pointed more directly towards the Sun (as seen on the left side of the picture above). On the other side of the orbit, six months later, it is pointed more away from the Sun (as seen on the right side of the picture above). When the Northern hemisphere is pointed towards the Sun, the days are longer, solar heating is more intense, and temperatures are higher - it is summertime! When the Northern hemisphere is pointed away from the sun, the days are shorter, solar heating less intense, and the temperatures are lower - it is winter! (Notice that when the Northern hemisphere is pointed toward the Sun, the Southern hemisphere is pointed away, and vice versa. So when it is summer in the north, it is winter in the south and vice versa.)

Milankovich found that Earth's tilt is not constant, but varies slightly over a cycle that lasts about 41,000 years. The change is small, but when the tilt is less, less snow melts in the polar regions because of the shorter days and reduced sunlight, allowing glaciers to form and spread. When the tilt is greater, more snow melts during the resulting long summers in the polar regions and glaciers tend to shrink.

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Orbital Changes
The Ice Ages
What Is an Orbit?
The Shape of Earth's Orbit
Image of a star. The Tilt of Earth's Axis
The Wobble of Earth's Axis

 

 
             
     
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Orbital Changes | The Ice Ages | What Is an Orbit? | The Shape of Earth's Orbit | The Tilt of Earth's Axis | The Wobble of Earth's Axis

Giant Impact | Super Nova | Disease | Volcanoes | Orbital Changes | Meet the Dinosaurs | Into the Future

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April 28, 2005

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