The intensity of light coming from the stars, of course, does not depend on the season, but visual perception is influenced by the celestial background. In summer time the Sun drops below the horizon in St. Petersburg only by 6 degrees, in Moscow – by 11 degrees. This means that pitch blackness does not come and twilight lasts the whole night.
Against such a background the luminaries look dimmer, and on winter nights the skies take on a darker colour. In addition, the number of bright stars actually increases during the winter period. For example, in summer, only 6 of the 25 brightest stars can be seen at 00:00, while in winter you can see 10, including the legendary Sirius.
In addition to illumination, the visibility of luminaries is influenced by the transparency of the air. Cold air contains less moisture than warm air. Because of this, the air is more transparent in winter.
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