Everyone is familiar with the experience of being outside, looking up at the sky, and suddenly you notice a faint white shape, which cannot be a cloud, but neither can it be an airplane – then it turns out that it is the moon and you can be happy or amazed, well, what are you doing here right now. It is the moon it often turns white even in the sky during the day, you just need to know when and where to look.
Let’s start with why the moon is visible. Ancient myths still treated our companion in space as a luminous celestial body: the Sun illuminates by day, the Moon by night, so it is also in folk tales. Of course, we have known for a long time that the Moon does not actually have a light of its own, but is illuminated by the Sun: what we see as moonlight is actually sunlight reflected off the surface of the Moon.
While it doesn’t look like it belongs here, it really does, so let’s take the school curriculum into consideration Because the sky is blue. The explanation for the phenomenon is the Rayleigh scattering, whose name was also known later in his life as Lord Rayleigh John William Strutttaken from. Strutt was one of the discoverers of argon and received the Nobel Prize in Physics for his work, but he also left a lasting impression on science at a young age when he described the aforementioned dispersion. The essence of this is that light is scattered by particles smaller than its wavelength: particles (in the case of the sky, mainly oxygen and nitrogen molecules) partially absorb light and partially transmit it in a different direction.
Sunlight is white light, which is made up of several colors and can be broken down into colors well with a prism. Different colors of light have different wavelengths, one of the shortest wavelengths being blue light. Which means that blue light is scattered far more than others, reflecting particles multiple times and eventually suppressing other colors. This is a very poor explanation, because other factors also play a role, for example, that purple light with an even shorter wavelength is better absorbed by the upper atmosphere, or that the human eye is more sensitive. to blue to purple. But the point is, blue light is more diffuse, that’s why we see blue sky. (And while we’re at it: sunset is orange because the sun’s rays reach our eyes at a different angle, through a thicker layer of the atmosphere, so most of the short-wavelength blue light is absorbed. and start red and yellow dominate.)
So nature during the day puts on a crazy laser show in the atmosphere, which obviously involves light pollution. The light of the stars is not even visible during the day, because their light rays are too faint to be noticed, they are suppressed by the atmospheric lights. The Moon, on the other hand, is very close to the Earth on a cosmic scale, its average distance from us is 384,400 kilometers. It also reflects strong sunlight well, so it is much brighter than a star, so much so that its outlines are often clearly visible through the atmosphere. But exactly when and where?
The answer to this question has long been known, recently by Edward Guinan, professor of astrophysics at Villanova University in Pennsylvania. He explained to Live Science. As Guinan said, around the new moon – that is, when the moon is not bright anyway – the moon is not visible during the day for two or three days, because at that time it is too close to the sun. The matter is further complicated by the cycle of the Moon and the seasons, which also depends on when and how high the Moon is. During the full moon, for example, the celestial body can only be seen at night, because then it is exactly 180 degrees from the Sun, that is, it falls below the horizon just as the Sun rises.
But overall, you can often get caught during the day, because the moon is above the horizon for about 12 hours a day. And when there is no full moon, it can be anywhere between 0 and 180 degrees to the Sun, which means it will theoretically appear in the daytime sky as well. The possible time windows for observing the Moon in sunlight are on average about 6 hours per day. This is also complicated by the seasons: in winter, when the days are shorter, the Moon receives less limelight (!) During the day, and of course it also matters where the observer lives, because in Spitsbergen, for example, the concept of daylight is difficult to understand in December.
If we exclude such exotic cases, it is theoretically possible to see the Moon during the day for about 25 days in a month (the remaining five days are around the full moon and the day of the new moon). But visibility is also affected by the weather, terrain and height of the moon (it’s not covered by a mountain, for example). And, of course, if we’re looking at the moon in the vast sky, because it’s actually often above us, but we don’t spend our days looking up at the sky.
According to Guinan, the moon is best seen in daylight in the first quarter, one week after the new moon, and in the third quarter, one week after the full moon. It is especially worth looking at the sky on days when the Moon is 90 degrees from the Sun. In the first quarter, the Moon should rise in the eastern sky in the afternoon. And in the third quarter in the morning hours, as it sets in the western sky.
