Why Earth has 4 seasons

earthsky.org | 9/23/2019 | Deanna Conners
Micaella (Posted by) Level 3
Click For Photo: https://en.es-static.us/upl/2013/10/fall-color-vermont-e1474312671616.jpg

Nearly everyone enjoys the change of seasons on Earth – from winter to spring, from summer to fall. But why do our seasons change?

Some assume our planet’s changing distance from the sun causes the change in the seasons. That’s logical, but not the case, for Earth. Instead, Earth has seasons because our planet’s axis of rotation is tilted at an angle of 23.5 degrees relative to our orbital plane – the plane of Earth’s orbit around the sun.

Tilt - Axis - Earth - Obliquity - Scientists

The tilt in the axis of the Earth is called its obliquity by scientists.

Obliquity. Image via Wikipedia.

Course - Year - Angle - Tilt - Words

Over the course of a year, the angle of tilt does not vary. In other words, Earth’s northern axis is always pointing the same direction in space. At this time, that direction is more or less toward the star we call Polaris, the North Star. But the orientation of Earth’s tilt with respect to the sun – our source of light and warmth – does change as we orbit the sun. In other words, the Northern Hemisphere is oriented toward the sun for half of the year and away from the sun for the other half. The same is true of the Southern Hemisphere.

When the Northern Hemisphere is oriented toward the sun, that region of Earth warms because of the corresponding increase in solar radiation. The sun’s rays are striking that part of Earth at a more direct angle. It’s summer.

Northern - Hemisphere - Sun - Sun - Rays

When the Northern Hemisphere is oriented away from the sun, the sun’s rays are less direct, and that part of Earth cools. It’s winter.

Seasons in the Southern Hemisphere occur at opposite times of the year from those in the Northern Hemisphere. Northern summer = southern winter.

Autumn - New - Jersey - Pinelands - Friend

Autumn in New Jersey’s Pinelands, by our friend Jeanette York. She said this is her backyard.

The tilt in Earth’s axis is strongly...
(Excerpt) Read more at: earthsky.org
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