According to the reporter of Mehr, Yalda night, as the longest night of the year, is one of the oldest calendar occasions in Iranian culture, which has deep roots in the history, rituals and lifestyle of the people of this land. this that night It has long been associated with family gatherings, storytelling, poetry reading and symbols of light and hope, and has always had a special place in Iran’s cultural calendar. However, Yalda is only one the occasion It is not traditional, but a completely scientific and astronomical phenomenon that is formed based on the movement of the earth and its position in relation to the sun.
Yalda night is the longest night of the year in the Northern Hemisphere and the reason for that is an astronomical phenomenon called “Winter Revolution”. At this moment, the axis of rotation of the earth with an angle of 23.5 degrees compared to its orbit around the sun, makes the sun to have the lowest height in the sky and the length of the night to the maximum.
Ali Ebrahimi Saraji, an expert in the field of calendar and astronomy, in an interview with Mehr reporter, explained the scientific details of this phenomenon and the difference in the length of the night in different places. different It explains Iran and the world.
Ali Ebrahimi Saraji, a member of the board of directors of the amateur branch of the Iranian Astronomical Society and an expert in the field of calendar, in a conversation with Mehr reporter about why the Yalda night is named as the longest night of the year, stated: From a scientific point of view, the longest night of the year occurs when the Earth enters the winter season in the Northern Hemisphere during its rotation around the sun, due to its axial inclination of 23.5 degrees. This moment, called the winter solstice, marks the official start of winter in the northern hemisphere.
He added: At the moment of the winter solstice, the sun is perpendicular to the orbit Ras Al Jadi shines and as a result, the length of the night reaches its maximum value in the northern hemisphere. In 1404, this moment occurs at 18:33 on Sunday, December 30, and at this time, we experience the longest night of the year.
This calendar expert refers to the difference in the length of the night at points different Zemin said: The length of Yalda night varies depending on the geographical location. As we get closer to the polar regions, the length of the night increases; So that in some areas near the North Pole, the sun may not rise for several days or even months.
Ebrahimi Saraji also said about the historical background of Yalda night: Yalda was originally a family celebration and the word “Yalda” means the birth of the sun. From this night onward, the length of the days gradually increases, and this has caused this night to be celebrated as a symbol of the victory of light over darkness since the distant past.
A member of the board of directors of the amateur branch of the Iranian Astronomical Society explained about the notion of the existence of “two long Yalda nights” in some years: sometimes, due to the time of the winter solstice and a slight difference in the calculation of the length of the night, two consecutive nights may have almost the same length in some areas. This issue depends on the time interval of each region from the exact moment of the winter solstice, and it is a completely natural and scientific phenomenon.
Referring to Iran’s situation in the longest night of the year, this astronomy expert said: This year, the longest night of the year is in the northwest of the country and in the border village. Boralan Located in West Azarbaijan province, it is recorded that the length of the night reaches 14 hours and 39 minutes. On the other hand, the shortest night of Yalda is related to the border village back port A village in Sindh province Mirthoban Central part of the city assistance It is in Sistan and Baluchistan province, where the night will be 13 hours, 25 minutes and 37 seconds.
He continued: In Tehran, the length of the night on the 29th and 30th of December is almost the same and reaches 14 hours, 16 minutes and 2 seconds.
Ebrahimi Saraji, in response to the question of whether the Yalda night phenomenon occurs only in the northern hemisphere, explained: In the southern hemisphere there is also the longest night of the year, but this time coincides with the summer solstice of the northern hemisphere. seasons They are completely reversed in the two hemispheres of the earth; That is, when it is winter in the northern hemisphere, the southern hemisphere is in summer.
In the end, he pointed to a common misconception and added: Earth’s proximity or distance from the sun does not play a role coldness Or it does not have the warmth of the seasons. Even the earth reaches its closest distance from the sun in the middle of January, but due to the axial inclination of the earth, winter is established in the northern hemisphere.
Based on Scientific calculations, the length of the night in points different The world is different depending on the latitude of each region. In the table below, the longest night of the year in eight capitals of the world, including Moscow, Oslo, Reykjavik, AtawaTokyo, Beijing, New Delhi, AddisfatherCaracas is presented:
This table shows that As we approach higher latitudes, the length of the night increases And in regions and countries that are near the North Pole, the length of the night even reaches more than 20 hours. In contrast, in areas near the equator, the length of night and day is almost equal and does not change much.
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