A month ago I have carried out an experiment to confirm or deny that moonlight lowers temperature of an object irradiated by it. The experiment, which I have made month ago, confirmed this thesis, but I made a systematic error during it, which undermined the credibility of the experiment. The error was that I covered the tip of the thermometer, which hindered the free convection of heat. This month around Full Moon I tried to eliminate this error. The experiment was set like in the picture above. The thermometer lied in a box with low walls, so that the tip was protected from the blasts of air, but that the light of the moon could easily fall on it. Additionally, I have set up a shield against wind gusts made from blue cardboard (fortunately, there was no wind, but weak gusts could disturb the measurement). For covering the tip of the thermometer from moonlight I used an aluminum plate placed at a distance from the thermometer. I did not want to disturb the convective air movement setting the plate too close. I have put the plate in front of the thermometer to shield it from the lunar rays, or in the back to illuminate the thermometer. I placed the plate at about the same distance in front and in the back the thermometer, to keep constant convection conditions. I have used this same thermometer which month ago: DT -11 made by the Termprodukt company wich was able to measure temperature with accuracy to 0.05 degree of Celsius.. Unfortunately, there were clouds in the sky that night and there was fog in the area, which made the measurement unbelievable.
During Full Moon it was cloudy time, so next experiment I have made just after Full Moon. I chose place where fog occurred rarely. I have set my experimental devices close to corrugated metal fence which additionally protected the thermometer against gusts of wind. Fortunately i was very calm. The experiment setting was exactly the same as in the first picture. In addition, I used a camera on a tripod to film the whole experiment. The setting of the test apparatus is shown in the picture on the left side. On the right side is an aluminum plate shielding the thermometer from lunar light. The experiment was as follows. For about 20 minutes after setting up the apparatus I waited about 20 meters away from the device until the temperature of the thermometer stabilized. The thermometer was exposed to moonlight that time. After 20 minutes I approached to the system, turned on the camera in film mode and walked away about 20 meters from the measuring system. Then after about 10 minutes I went to the system and moved the aluminum plate behind the measuring system. The time when the thermometer was covered by the aluminium plate, and when it was exposed to moonlight was about 10 minutes. I made two such cycles, i.e. the experiment time was about 40 minutes.
Measurement started when the thermometer was exposed. As you can see in the video at this link, the temperature started to rise from 11.24 ° C and then fluctuated between 11.26 ° C to 11.30 ° C throughout the measurement period. At the moment when I approached to the system to cover it from the moonlight, the temperature was 11.26 ° C (Footsteps and the sound of moving the plate can be heard at about 10 minutes and 30 seconds of the movie). After covering, the temperature was 11.33 ° C. Then, when I went away, it dropped to 11.24 ° C, which was probably caused by air movement, and then raised oscillating to 11.38 ° C at the end of this part of the measurement. Then I unhid the thermometer (about 20 minutes 40 seconds at the movie) and the temperature began to drop down from 11.36 ° C to 10,81 ° C at the end of this measurement section (30 minutes 20 seconds you can hear the steps at the film and the sound of moving the plate). I moved the plate again to cover the thermometer and walked away. The plate was in the same place where it was during the first hiding cycle, but I noticed that the Moon has moved in the sky and the plate did not cover the tip of the thermometer anymore. Moonlight was falling on the thermometer. If there was any movement of air cooling the thermometer, then, as in the first cycle, the plate should stop it. Before there was an increase in temperature but that time a fall. The temperature dropped oscillating from 10.80 ° C to 9.88 ° C. The last recorded measurement is 10.05 ° C when I was turning the camera off. The increase in temperature probably was caused by my presence near the research set. I decided to repeat the measurement. I made a second movie, but the battery in the camera was exhausted and I was able to register only one full cycle. The film can be seen at this link. As you can see in the movie when the thermometer was covered, the temperature has increased from 10,08 ° C to 10,31 ° C. During the exposure for moonlight it dropped from 10.36 ° C to 9.83 ° C.
And what conclusions can be drawn from the experiment?
This experiment suggests that there is some factor not related to convection, by which some people try to explain the phenomenon of the moonlight cooling, which causes the objects to cool down when the moonlight hits them. It seems that the cooling factor comes from the side of the Moon. The aluminum plate holds it back.
So what can it be?
Visible light does not heat or cool objects. But what about infrared radiation?
The website livescience.com informs us:
"Everything with a temperature above about 5 degrees Kelvin (minus 450 degrees Fahrenheit or minus 268 degrees Celsius) emits IR radiation."
And what about Moon's temperature?
The space.com explains:
"When sunlight hits the moon's surface, the temperature can reach 260 degrees Fahrenheit (127 degrees Celsius). When the sun goes down, temperatures can dip to minus 280 F (minus 173 C)."
My guess is that the Moon warms up and colds only at the outermost layer to a depth of several dozens, maybe several hundreds meters. We do not know so much about Moon's interior. Only hypothesis. It could be that the entire interior of the Moon has a constant average temperature of around -23 ° C. We know from the pictures of the surface of the Moon that it has a gray color. So we can treat the whole Moon as a gray body. The maximum intensity of the gray body radiation (Wien's displacement law) determines the identical pattern as for the black body, that is, the shorter wave the higher temperature - inverse proportion. Stefan - Boltzmann's law is almost identical to that for a black body, that is, the power emitted by the surface unit is proportional to the fourth power of temperature. For the temperature of -23 ° C (150.15 K) the most of energy the Moon radiates in the infrared wave form with wavelength 0.00193 cm, that is 1.93 x 10-5 m.
From everyday experience, we know that if we have, for example, a piece of ice, we do not have to touch it to feel its cold. It is enough to bring a hand closer. If we hold our hand near to the ice piece and feel its coolness, it is not a convection or some other flow of cold air, but we sense the infrared radiation of the object. So we can hypothesize that the cooling factor for the thermometer in the experiment described above is infrared radiation with a wavelength of 1.93 x 10-5 m corresponding to the temperature of -23 ° C. If the hypothesis is true, the Moon should cool the objects also in other phases in addition to the Full Moon. And even the result should be better, because measurement will be less distorted by the warm Moon's surface. The best results should be around the new moon.
Measurement started when the thermometer was exposed. As you can see in the video at this link, the temperature started to rise from 11.24 ° C and then fluctuated between 11.26 ° C to 11.30 ° C throughout the measurement period. At the moment when I approached to the system to cover it from the moonlight, the temperature was 11.26 ° C (Footsteps and the sound of moving the plate can be heard at about 10 minutes and 30 seconds of the movie). After covering, the temperature was 11.33 ° C. Then, when I went away, it dropped to 11.24 ° C, which was probably caused by air movement, and then raised oscillating to 11.38 ° C at the end of this part of the measurement. Then I unhid the thermometer (about 20 minutes 40 seconds at the movie) and the temperature began to drop down from 11.36 ° C to 10,81 ° C at the end of this measurement section (30 minutes 20 seconds you can hear the steps at the film and the sound of moving the plate). I moved the plate again to cover the thermometer and walked away. The plate was in the same place where it was during the first hiding cycle, but I noticed that the Moon has moved in the sky and the plate did not cover the tip of the thermometer anymore. Moonlight was falling on the thermometer. If there was any movement of air cooling the thermometer, then, as in the first cycle, the plate should stop it. Before there was an increase in temperature but that time a fall. The temperature dropped oscillating from 10.80 ° C to 9.88 ° C. The last recorded measurement is 10.05 ° C when I was turning the camera off. The increase in temperature probably was caused by my presence near the research set. I decided to repeat the measurement. I made a second movie, but the battery in the camera was exhausted and I was able to register only one full cycle. The film can be seen at this link. As you can see in the movie when the thermometer was covered, the temperature has increased from 10,08 ° C to 10,31 ° C. During the exposure for moonlight it dropped from 10.36 ° C to 9.83 ° C.
And what conclusions can be drawn from the experiment?
This experiment suggests that there is some factor not related to convection, by which some people try to explain the phenomenon of the moonlight cooling, which causes the objects to cool down when the moonlight hits them. It seems that the cooling factor comes from the side of the Moon. The aluminum plate holds it back.
So what can it be?
Visible light does not heat or cool objects. But what about infrared radiation?
The website livescience.com informs us:
"Everything with a temperature above about 5 degrees Kelvin (minus 450 degrees Fahrenheit or minus 268 degrees Celsius) emits IR radiation."
And what about Moon's temperature?
The space.com explains:
"When sunlight hits the moon's surface, the temperature can reach 260 degrees Fahrenheit (127 degrees Celsius). When the sun goes down, temperatures can dip to minus 280 F (minus 173 C)."
My guess is that the Moon warms up and colds only at the outermost layer to a depth of several dozens, maybe several hundreds meters. We do not know so much about Moon's interior. Only hypothesis. It could be that the entire interior of the Moon has a constant average temperature of around -23 ° C. We know from the pictures of the surface of the Moon that it has a gray color. So we can treat the whole Moon as a gray body. The maximum intensity of the gray body radiation (Wien's displacement law) determines the identical pattern as for the black body, that is, the shorter wave the higher temperature - inverse proportion. Stefan - Boltzmann's law is almost identical to that for a black body, that is, the power emitted by the surface unit is proportional to the fourth power of temperature. For the temperature of -23 ° C (150.15 K) the most of energy the Moon radiates in the infrared wave form with wavelength 0.00193 cm, that is 1.93 x 10-5 m.
From everyday experience, we know that if we have, for example, a piece of ice, we do not have to touch it to feel its cold. It is enough to bring a hand closer. If we hold our hand near to the ice piece and feel its coolness, it is not a convection or some other flow of cold air, but we sense the infrared radiation of the object. So we can hypothesize that the cooling factor for the thermometer in the experiment described above is infrared radiation with a wavelength of 1.93 x 10-5 m corresponding to the temperature of -23 ° C. If the hypothesis is true, the Moon should cool the objects also in other phases in addition to the Full Moon. And even the result should be better, because measurement will be less distorted by the warm Moon's surface. The best results should be around the new moon.