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The Sun's Angle & Movement

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  • 0:00 What are Seasons?
  • 1:15 Position of the Sun
  • 2:15 Long Days and Short Days
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain how the Sun's movement in the sky varies with the seasons and how that relates to the length of each day. A short quiz will follow.

What Are Seasons?

Seasons are divisions that break the year into four parts (spring, summer, autumn, and winter) that tend to have distinctive types of weather and hours of daylight. Some parts of the world have bigger differences between the seasons than others.

Spring is the time when vegetation starts to appear after winter and is from March until May in the northern half of the Earth (the Northern Hemisphere) and September until November in the southern half of the Earth (the Southern Hemisphere).

Summer is the warmest season of the year and comes after spring, at a time when most vegetation has already appeared. It runs from June to August in the Northern Hemisphere and from December to February in the Southern Hemisphere. Summer has more hours of daylight than any other season.

Autumn follows summer and is when crops and fruits are collected from farmers' fields, and the leaves of deciduous trees fall to the ground. It's from September to November in the Northern Hemisphere and from March to May in the Southern Hemisphere.

And winter is the coldest season of the year when deciduous trees have already lost their leaves, and plants and animals will often hibernate to escape the cold. It goes from December to February in the Northern Hemisphere and from June to August in the Southern Hemisphere.

But why does the Earth have seasons? What causes them?

Position of the Sun

Well, it's all to do with the position of the Sun in the sky. The Earth orbits around the Sun, but the Earth is also tilted to one side at an angle of 23.4 degrees. The Earth's spin axis doesn't point at 90 degrees to the Sun. Because of this, the Northern Hemisphere is tilted towards the Sun in the Northern Hemisphere's summer and tilted away during winter. This tilting causes the seasons. But how?

A lot of people think that it's because when you're tilted towards the Sun, it's warmer because you're closer to the Sun, but this isn't true. While you are closer to the Sun while tilted, the difference is tiny and wouldn't cause seasons. Instead, it's all about the angle of the Sun's rays on the Earth.

When your half of the Earth is tilted towards the Sun, the Sun's rays are more concentrated. When the Earth is tilted away from the Sun, the Sun's rays are more spread out over a larger surface. Another way of thinking about this is that, in the summer, the Sun will be higher in the sky. And in the winter, the Sun will be lower in the sky. This, not distance, is why we have the seasons.

Long Days and Short Days

The position of the Sun in the sky also affects the length of each day. The Sun rises in the east and sets in the west. But in the winter, the Sun takes an arc across the sky that is close to the southern horizon if you're in the Northern Hemisphere and close to the northern horizon if you're in the Southern Hemisphere. It takes a low path in the sky, a shorter path, and isn't above the horizon for as long. This makes the day short in the winter.

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