The starry sky as your free refrigerator

Surely you have read novels about travelers in your childhood, and you remember how important a decent night’s rest was in their lives.

Both Dumas’ musketeers, London’s gold prospectors, and all the heroes of the Wild West without exception agreed on one thing: it’s better to travel an extra 10 miles than to sleep under the open sky.

Why?

Yes, no one likes getting wet in the rain and cooking over a campfire, those are answers that are obvious.
But there is another, less obvious reason. Even in very warm countries, even in the summer in the desert, sleeping without a tent under the starry sky can make you very cold.

The thing is this. The radiative temperature of the clear starry sky from the Earth’s surface can be 20°C, or even 30°C, lower than the temperature of the night air. It’s understandable. Space itself does not emit anything (we can neglect relic radiation in this case). And the Earth’s atmosphere, along with dust, water vapor, and even greenhouse gases, doesn’t add that much. So, at an air temperature of +15°C at the surface, the radiative temperature of the sky can easily be −15°C. This means that any object under such a sky will quickly lose heat due to its own radiation. More precisely, due to the difference between the energy that the object radiates into the sky itself and what comes back as radiation from above. Since the intensity of heat loss through radiation is proportional to the 4th power of the absolute temperature, the effect is quite significant.

For this reason, even on a warm summer night in open areas, dew forms (under a shelter, where there is no direct contact with the sky, there is no dew).

For the same reason, it is more comfortable to sleep in a tent even on a clear night.

And if you want to cool a room a bit in a hot climate, it’s better to open the curtains at night. During the day, however, you will need to close the curtains again, otherwise the sun will return much more heat to you than you gave away during the night.

Therefore, it is very convenient to have a smart home with automatic curtains that understand when to open and when to return to their original position. By the way, following the same principle, in winter smart curtains can heat a room. Letting in maximum sunlight during the day, and on the contrary, retaining radiation inside at night.

Switching smart curtains between summer and winter modes is another task that a smart home handles excellently. You just need to install a couple of temperature sensors and a light sensor.