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Role of sun

Day after day, season after season, the sun shines steadily. The sun heat up the earth - both land and water. The earth in turn heats up the air around it. The air is responsible for distributing the heat in the atmosphere. In short whatever happens in the atmosphere is due to the sun. The sun is the primary cause of all weather changes. But without the atmosphere and water, there would have been no weather.

The sun’s role in defining weather is dependent on

  1. The number of hours of sunlight received.
  2. Whether the sun’s rays are direct or slant

Heating of earth

Step outside in summer. If you are bare footed, you will notice that the ground is very hot. Where did that heat come from? Of course from the sun.

If you leave a piece of dark paper in the sunlight for five minutes, it will feel hot when touched. Put another dark paper next to it for only one minute, and you will find that it is only slightly warm The more time in the sun, warmer it gets. Heat accumulates.

Duration of sunlight

Duration of sunlight is one reason why the weather is different at different times of the year. Days (daytime or sunlight hours) in winter are shorter than those in summer. This effect is less noticeable at places near the equator that away from it. In fact, at the poles, the sun never sets in summers and never rises in winters. The sun gets less time to heat the ground in winter than in summer. More hours of sunlight there are, the warmer is the weather. So July days are warmer than December days (in the northern hemisphere, while the opposite is true - July days are cooler than December days in the southern hemisphere).

On a cloudy day, most of the sunlight is blocked off by the clouds. The earth is not warmed as much as it is on a clear day. So a cloudy day is usually cooler than a sunny day.

Slant and direst sunlight

There's another reason, for winter days being cold and summer days being warm. Winter sunlight is cooler! It's the same sun, and it shines just as bright and hot as in the summertime and yet the earth gets less heat from it.

How can the same sun give less heat at one time than another? Is it because we are closer to the sun in summer than we are in winter? Definitely not! Look at the distances between the sun and earth in December and June!

The reason that winter sunlight is cooler is because the sun's rays come to us at much more of a slant than they do in summer. You may have noticed that the afternoon sun on a winter's day is lower in the sky than what it is in summer. That is, the sun is almost overhead in summer whereas, it is not so in winter.

Winter and summer, the sun itself is the same, but the way it shines on the earth is different and therefore the amount of heat the earth receives is different. Winter is colder than summer for two reasons—there are fewer hours of sunlight per day, and the sun's rays are more slanting and therefore give less heat.

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