January 10, 2016 at 02:19Ask Ethan No. 42: Does the Sun shine brighter in summer?
- Transfer
In the hottest moments of the seasons - in the summer in the northern hemisphere, and in the winter in the southern - you are probably waiting for one of the following phenomena:
- warm, bright, long sunny days
- cold, short, cloudy days that are best spent at home
But why are these are days getting like this? The reader asks:
Without a doubt, the difference in the apparent brightness of the sun on the days of summer and winter solstices is quite noticeable.
For readers living outside the tropics (at latitudes of more than 23.4 °), the summer solstice, when the sun approaches its zenith most strongly, is familiar. During the winter solstice, the maximum rise in the sun above the horizon is 46.8 ° less than during the summer solstice.
And this difference can not only be seen, but also felt - by temperature!
There is no doubt that the sun at its zenith is felt more intense than not high above the horizon. Therefore, even without taking into account the delay in warming the atmosphere, closer to noon the temperature is higher than in the morning or after sunset.
But is the sun at its zenith brighter?
Not really. You must have heard about 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 radiation intensity of the sun changes by 0.1%. This can hardly be felt.
On the other hand, one may wonder about the distance from the Earth to the Sun. Earth moves in an elliptical orbit. Is it possible that the intensity of the radiation reaching us changes due to changes in the distance to the Sun?
But this also has an extremely small impact. At the minimum distance from the Sun, we get energies of 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 originating 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 W per sq.m. are transferred to that square meter on which you are. But if the Sun is at an angle, this energy is distributed over a much larger area.
If you recall trigonometry, then the amount of energy 1366 ± 0.1% ± 6% must be multiplied by the cosine of the angle deposited from the zenith.
A 6.1% variation in intensity is equivalent to a difference of 3.5 ° in the angle of the Sun. The main effect is that the energy is distributed over a larger area, so less of it reaches the place where you are.
The second effect is that light from the Sun needs to go through the atmosphere.
The atmosphere is able to scatter radiation, including sunlight. When the sun is above our heads (90 °), light has to travel 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 the summer solstice, and 272 km at noon in the winter - almost 3 times more!
Therefore, sunsets and sunrises, although beautiful, do not give heat at all. This means that neither our distance from the sun, nor fluctuations in its intensity affect the intensity of 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 go through.
- warm, bright, long sunny days
- cold, short, cloudy days that are best spent at home
But why are these are days getting like this? The reader asks:
It seems to me that in 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 summer and winter solstices is quite noticeable.
For readers living outside the tropics (at latitudes of more than 23.4 °), the summer solstice, when the sun approaches its zenith most strongly, is familiar. During the winter solstice, the maximum rise in the sun above the horizon is 46.8 ° less than during the summer solstice.
And this difference can not only be seen, but also felt - by temperature!
There is no doubt that the sun at its zenith is felt more intense than not high above the horizon. Therefore, even without taking into account the delay in warming the atmosphere, closer to noon the temperature is higher than in the morning or after sunset.
But is the sun at its zenith brighter?
Not really. You must have heard about 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 radiation intensity of the sun changes by 0.1%. This can hardly be felt.
On the other hand, one may wonder about the distance from the Earth to the Sun. Earth moves in an elliptical orbit. Is it possible that the intensity of the radiation reaching us changes due to changes in the distance to the Sun?
But this also has an extremely small impact. At the minimum distance from the Sun, we get energies of 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 originating 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 W per sq.m. are transferred to that square meter on which you are. But if the Sun is at an angle, this energy is distributed over a much larger area.
If you recall trigonometry, then the amount of energy 1366 ± 0.1% ± 6% must be multiplied by the cosine of the angle deposited from the zenith.
A 6.1% variation in intensity is equivalent to a difference of 3.5 ° in the angle of the Sun. The main effect is that the energy is distributed over a larger area, so less of it reaches the place where you are.
The second effect is that light from the Sun needs to go through the atmosphere.
The atmosphere is able to scatter radiation, including sunlight. When the sun is above our heads (90 °), light has to travel 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 the summer solstice, and 272 km at noon in the winter - almost 3 times more!
Therefore, sunsets and sunrises, although beautiful, do not give heat at all. This means that neither our distance from the sun, nor fluctuations in its intensity affect the intensity of 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 go through.