Sunset and sunrise. Duration of daylight hours.

Such astronomical phenomena as sunset and sunrise occur every day at different times and only due to rotation around the Sun. In another case, the heavenly body would be in a permanent zenith, which would deprive the Earth of not only sunrises and sunsets, but life itself on the planet would be impossible.

Sunset and sunrise

Sunset and sunrise are called intervals of time, when the upper edge of the Sun is at the same level as the horizon line. The trajectory of the passage of the heavenly body differs depending on which point of the planet and at what time of the year to observe it. At the equator, the Sun rises perpendicularly from the horizon and also goes perpendicular, regardless of the season.

Where does the Sun rise?

Most people know that the sun rises in the east and sets in the west. However, this is nothing more than a generalization. In fact, this happens only 2 days a year - during the spring and autumn equinox. On other days the sun rises from north to south. Every day, the points at which the sun sets and the sun rises slightly. On the day of the summer solstice, it rises to the maximum to the northeast. Every day after that the luminary rises slightly to the south. On the day of the autumnal equinox, the sun rises strictly in the east and sets in the west.

Since ancient times people have been monitoring the growth and parameters of the points of sunrise and sunset with great detail. Thus, in antiquity it was possible to orientate in time with the help of the jagged peaks of mountains along the horizon line or with the help of standing stones arranged in a special way.

End and beginning of daylight hours

Sunset of the Sun and sunrise are the points of the beginning and end of the light day. It is important to note that both of these phenomena are only short instants. Twilight is the time range during which the day becomes night or vice versa. In the morning twilight is the time between sunrise and sunrise, and the evening time is the time between sunset and sunset. The duration of twilight actually depends on the location on the planet, as well as on a certain date.

For example, in the Arctic and Antarctic latitudes, a winter night is never completely dark. The sunrise is the moment when the upper edge of the Sun becomes visible above the eastern horizon in the morning. Sunset is the moment when the trailing edge of the Sun ceases to be visible and disappears below the western horizon in the evening.

Duration of daylight hours

The duration of a light day, and with it the time of sunset and sunrise, is not a constant value. In the northern hemisphere, the days are longer in summer, and in winter the days are shorter. The duration of daytime also decreases or increases depending on geographical latitude, the higher it is, the shorter the days. As a rule, this is winter time. An interesting fact is that due to the decrease in the Earth's rotation speed , the days become a little longer with the passage of time. About 100 years ago, the average day was 1.7 milliseconds shorter than now.

Sunrise is the sunset. What is the external difference?

Sunrises and sunsets look different. Is it possible to visually establish these differences if one looks at how the sun rises above the horizon, without knowing whether the day ends or just begins? So, is there an objective way to distinguish these two similar phenomena? All twilight intervals are symmetrical. This means that between them there is no big optical difference.

Nevertheless, two human factors deny their identity. Closer to sunset, the eyes, adapted to daylight, begin to get tired. Gradually, the light disappears, the sky darkens, and a person can not adapt as quickly as all this happens. Some shades can not be fully appreciated. At dawn, the situation is quite different.

Night darkness adapts vision to a very sharp and clear vision, and every unobtrusive color change in the sky immediately catches your eye. Thus, more colors are perceived at dawn than in the evening twilight. It is this time because of the limited visibility is the most dangerous for drivers, so there is a need for artificial lighting. With the onset of twilight, you must always include lights.