Is it true that in the afternoon of a deep well you can see the stars?

It is generally accepted that the heavenly luminaries, which the human eye is not able to distinguish in the daytime sky, are visible from the depths of the dark well. We checked if it was true.

This is an interesting natural phenomenon since antiquity. Also Aristotle in his work "On the emergence of animals" He wrote: “This does not happen together: the one who, shading his eyes with his hand or looking through the tube, still does not perceive the differences in the color, will see better into the distance: such stars sometimes see such from pits and wells.” Pliny Senior Claimedthat it is about the observation of stars in the afternoon when they look incomparably smaller. We have not forgotten about the effect and in much later times. So, German astronomer of the XVII century Christoph Sheiner He wrote: “I was told by one very educated and worthy confidence in the Spaniard, that everyone knows in Spain, that in open deep wells heaven and stars, brilliantly through reflection, as in the mirror, are very clearly visible at noon and that he himself often saw this with his own eyes ...” His French colleague Francois Arago took a whole chapter in his head in his head in his head in his head in his head in his head book "Generally permanent astronomy" (1861). There, in particular, he refers to the famous scientist John Gershel, who reported: “Bright stars passing through Zenit can even be visible by a simple eye with persons who are at the bottom of a deep and narrow hollow, such as a well or ore mine.”

Naturally, many physicists and astronomers of the past tried to test this statement experimentally - this method, if successful, could immediately put an end to disputes. German natural scientist and traveler of the 19th century Alexander Humboldt with his students I tried it To consider the stars through a chimney 230 feet high (70 m) and a hole with a diameter of 16 feet (5 m) - to no avail, even binoculars did not help. A similar result was waiting for him after going into the deep mines of Siberia and America. People did not leave their attempts in the 20th century. So, in 1978, the correspondent of Komsomolskaya Pravda Leonid Repin He wrote: “They say that in broad daylight you can see the stars in the sky if you go into a deep well. Once I decided to check if this was true, went down to a sixty -meter well, and I could not see the stars. Only a small square of a dazzling blue sky. " In 1992, in the journal Skeptical Inquirer about its similar failure told American tester Richard Sanderson.

However, practical experiments have their own drawback: in the case of local failure, it is impossible to give an unambiguous answer “no”, because there may be a lot of little things that need to be taken into account to achieve success. As for the theory, then, for example, the aforementioned Francois Arago believed his famous predecessors Hershel and Scheiner, and the justification proposed the following: “It seems to me that this phenomenon is explained very simply. The angle of view of our naked eye exceeds 100 °, therefore, a motionless eye facing the heavenly vault receives rays from all points of the atmosphere occupying a circular space of more than 100 ° in the diameter. ” Further, Arago claims that these rays passing through the eyeball, pour the retina with distracted light, against which the weak image of the star does not stand out. However, if, using a long tube, not allowing to enter the cornea of ​​most of the world, “stars concentrated at one point of the retina will take the advantage over the illumination of the same point directly and by scattering”.

It seems to sound logical. Indeed, in the afternoon the sky seems to us too bright because of the multiple sunlight. If multiple light weakens (for example, due to a complete sunny eclipse), bright stars and planets will become perfectly visible in the afternoon, as they are visible from the surface of the moon. What is the reason for this effect?

For this, it is necessary to consider the mechanism of our vision. Light falls into the eye through the pupil - an analogue of the opening of the lens diaphragm. Eye lenses - cornea and crystal - focus the light and create an image on the posterior surface of the eye, covered with a photosensitive layer - a retina, which includes a large number of receptors: column and sticks. Each receptor cell transfers information to the brain about the stream of light falling on it, and the brain synthesizes the whole picture of what is seen from these individual signals.

When we observe the star at night, the stream of light from it by one receptor, although small, is significantly superior to the flow from the dark sky that falls on neighboring cells. Therefore, the brain fixes this as a significant signal. However, in the afternoon, so much light from the sky falls on the receptors that a small additive in the form of a star of a star, reaching one of the receptors, is not felt by the brain as a real difference in light flows. So the star can become visible against the background of the daytime sky only when the flow of light from it is compared with the stream from the site of the sky, which the pupil projects onto one photosensitive cage. The angular size of this site is called the resolution of the eye and is in humans only 1-2 minutes, that is, 30-60 times less than 1 degree. Of all the brightest heavenly objects, with the exception of the Sun, only the Venus planet can provide such conditions, due to which is sometimes really visible in the daytime sky. All other planets and stars have shine much weaker, so it is impossible to see them without a telescope during the day - it doesn’t matter from the well or from the surface of the earth. There were separate cases when people managed to discern the planet Jupiter, however, in relation to Sirius, the brightest star of our sky, at least at the sea level, it is impossible to achieve such success.

Thus, the bright background of the sky reduces the contrast between the image of the star and the sky on the retina of the eye, making the star invisible. The hole of the pipe or well does not solve this problem, since the angular size of the observed objects is unchanged, and to comply with the necessary conditions, as showed The astronomer Vladimir Surdin, the depth of such a well should be at least 3400 m with a diameter of 1 m. However, as the scientist writes, "even at the same time, only a light point will be visible to the observer, the brightness of which will increase by several seconds if any star passes exactly through the zenith." And the probability of passing a bright star through Zenith is so small that this would have to wait for more than one millennium.

Another thing is the telescope, which can increase not only the flow of light from the star, but also the angular size of the observed objects. At the same time, the same site of the sky is projected onto a larger number of retinal receptors, and, therefore, each of them accounts for in proportion to less than light. Thanks to this, at least bright stars can be seen through this useful device in the afternoon. However, the presence of a telescope is a rather specific condition that was clearly not taken into account by either scientists of antiquity or astronomers of the recent past, who believed in this myth.

Not true

What do our verdicts mean?

Read on the topic:

1. V. G. Surdin. Stars.