Ask Ethan # 42: Does the sun shine brighter in the summer?
In the hottest moments of the seasons - in the summer in the northern hemisphere, and in the winter in the southern - you probably expect one of the following phenomena:
- warm, bright, long sunny days
- cold, short, overcast days that are best spent at home
But why are these days becoming such? The reader asks:
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Without a doubt, the difference in the apparent brightness of the sun on the days of the summer and winter solstices is quite noticeable.
For readers living outside the tropics (at latitudes over 23.4 °), the summer solstice is customary, when the sun approaches the zenith the hardest. During the winter solstice, the maximum rise of the sun above the horizon is 46.8 ° less than during the summer.
And this difference can not only be seen, but also felt - by temperature!
There is no doubt that the sun at the zenith is felt more intense than low above the horizon. Therefore, even without taking into account the delay in the warming of the atmosphere, the temperature is higher by noon than in the morning or after sunset.
But is the sun really brighter at the zenith?
Not really. You have probably heard of solar cycles and intensity fluctuations. Moreover, these fluctuations are relatively small. In the upper part of the Earth’s atmosphere, the received energy per unit area is from 1365.5 W / m 2 to 1366.5 W / m 2 .
In other words, the intensity of the sun's radiation changes by 0.1%. It can hardly be felt.
On the other hand, one can ask the question of the distance from the Earth to the Sun. The earth moves in an elliptical orbit. Is it possible that the intensity of the radiation reaching us changes due to a change in the distance to the Sun?
But this also has a very small impact. At the minimum distance from the Sun, we receive energy by only 6% more than at the maximum (intensity is inversely proportional to the square of the distance). 6% more than 0.1%, but still negligible.
In fact, the intensity is mainly influenced by two effects resulting from the same phenomenon: the tilt of the axis.
When the light from the Sun reaches the Earth, and the Sun is right above your head, then all these 1366 watts per square meter transferred to the square meter where you are. But if the sun is at an angle, this energy is distributed over a much larger area.
If we recall trigonometry, then the amount of energy 1366 ± 0.1% ± 6% must be multiplied by the cosine of the angle deposited from the zenith.
The variation of intensity by 6.1% turns out to be equivalent to a difference of 3.5 ° in the angle of the Sun's location. The main effect is that energy is distributed over a larger area, so less of it reaches the place where you are.
The second effect is that the light from the sun must pass through the atmosphere.
The atmosphere can diffuse radiation, including sunlight. When the sun is above us (90 °), the light has to pass about 100 km of the atmosphere. And if it is at an angle of 45 ° - then 141 km of the atmosphere, which greatly reduces its intensity.
Generally speaking, at my latitude, about 45 °, sunlight passes through 108 km of the atmosphere at noon of the summer solstice, and 272 km at noon of the winter - almost 3 times more!
Therefore, sunsets and sunrises, although beautiful, do not give any heat at all. This means that neither our distance from the sun nor the fluctuations of its intensity affect the intensity of the light reaching us. This is affected only by the angle at which the rays fall on the earth’s surface and the thickness of the atmosphere they have to pass.
- warm, bright, long sunny days
- cold, short, overcast days that are best spent at home
But why are these days becoming such? The reader asks:
')
It seems to me that in the summer the sun shines brighter. But if we take into account the change in the distance from the Earth to the Sun during the year, can there really be such a difference in brightness?
Without a doubt, the difference in the apparent brightness of the sun on the days of the summer and winter solstices is quite noticeable.
For readers living outside the tropics (at latitudes over 23.4 °), the summer solstice is customary, when the sun approaches the zenith the hardest. During the winter solstice, the maximum rise of the sun above the horizon is 46.8 ° less than during the summer.
And this difference can not only be seen, but also felt - by temperature!
There is no doubt that the sun at the zenith is felt more intense than low above the horizon. Therefore, even without taking into account the delay in the warming of the atmosphere, the temperature is higher by noon than in the morning or after sunset.
But is the sun really brighter at the zenith?
Not really. You have probably heard of solar cycles and intensity fluctuations. Moreover, these fluctuations are relatively small. In the upper part of the Earth’s atmosphere, the received energy per unit area is from 1365.5 W / m 2 to 1366.5 W / m 2 .
In other words, the intensity of the sun's radiation changes by 0.1%. It can hardly be felt.
On the other hand, one can ask the question of the distance from the Earth to the Sun. The earth moves in an elliptical orbit. Is it possible that the intensity of the radiation reaching us changes due to a change in the distance to the Sun?
But this also has a very small impact. At the minimum distance from the Sun, we receive energy by only 6% more than at the maximum (intensity is inversely proportional to the square of the distance). 6% more than 0.1%, but still negligible.
In fact, the intensity is mainly influenced by two effects resulting from the same phenomenon: the tilt of the axis.
When the light from the Sun reaches the Earth, and the Sun is right above your head, then all these 1366 watts per square meter transferred to the square meter where you are. But if the sun is at an angle, this energy is distributed over a much larger area.
If we recall trigonometry, then the amount of energy 1366 ± 0.1% ± 6% must be multiplied by the cosine of the angle deposited from the zenith.
The variation of intensity by 6.1% turns out to be equivalent to a difference of 3.5 ° in the angle of the Sun's location. The main effect is that energy is distributed over a larger area, so less of it reaches the place where you are.
The second effect is that the light from the sun must pass through the atmosphere.
The atmosphere can diffuse radiation, including sunlight. When the sun is above us (90 °), the light has to pass about 100 km of the atmosphere. And if it is at an angle of 45 ° - then 141 km of the atmosphere, which greatly reduces its intensity.
Generally speaking, at my latitude, about 45 °, sunlight passes through 108 km of the atmosphere at noon of the summer solstice, and 272 km at noon of the winter - almost 3 times more!
Therefore, sunsets and sunrises, although beautiful, do not give any heat at all. This means that neither our distance from the sun nor the fluctuations of its intensity affect the intensity of the light reaching us. This is affected only by the angle at which the rays fall on the earth’s surface and the thickness of the atmosphere they have to pass.
Source: https://habr.com/ru/post/371587/
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