On the summer solstice, the sun is direct.

At 17:13 and 40 seconds on June 21, the sun will be reappeared from the north. We will usher in the annual "Summer Solstice Day", and all areas in the northern hemisphere will also usher in the longest day of the year. On the same day, the sunrise time of Guangzhou was 41 minutes and 54, the sunset time was 19:15 and 28 seconds, and the day length was 13 hours, 33 minutes and 34 seconds. In Guangzhou, you can see the landscape of "no shadow".

Some people may be puzzled: Guangzhou seems to be in the south of the Tropic of Cancer in most areas, and it cannot usher in the "direct sunlight" on the summer solstice. Therefore, Guangzhou cannot appear "no shadow" on the summer solstice. In fact, the North Tropic is through the northern part of Guangzhou, and citizens can watch the astronomical landscape of the summer solstice on the day of the summer solstice.

According to reports, the North Torter Tetan Signing Tower, located on the land of Sanjiapo Village, Taiping Town, Conghua District, Guangzhou, is 42 kilometers from Guangzhou City. It is currently the highest and largest logo tower in the world's north -south background. At 12:27 44.84 seconds on June 21, the sun will be directly shot from Huaei to the backbone logo tower. The formation of this landscape is due to at noon on June 21st this year (summer solstice).

The North Tropic is actually "non -fixed". Due to the influence of astronomical factors such as the age difference, chapter movement, and extreme shift, it has become a "drift" weft of the geography. It is understood that there are about 25,800 years of astronomical cycle in the age. Zhangyong has a astronomical cycle of about 18.6 years, and has a variety of astronomical cycles of about 14 months. Therefore, there is a complex astronomical cycle of Huangchijiao (North Cancelona). A complete North Tropic of Northern and South mobile cycles is about 37170 years, and the half cycle is about 18585. According to the calculation, the maximum value of the last North Torter line occurred around 7283 BC, and its latitude value was 24 degrees, 14 minutes, 38.67 seconds. The minimal value (south) of the next North Tropic will occur around 11301, and its latitude value is 22 degrees, 37 minutes, 56.04 seconds. At present, the Northern Cancer is about 0.46845 seconds per year, that is, the average of about 14.41 meters south per year.

Summer solstice is the longest day in the northern hemisphere throughout the year, but it is not the earliest day of sunrise and the latest day of sunset throughout the year. This is because the orbit surrounded by the sun is not a round, but an ellipse. The sun is located on an focus of the ellipse. The distance between the earth and the sun is not equal every day, producing "true sun", but for the convenience of daily production and life, people formulate the "Pingtai Sun" used by our daily clocks. "The averageization of the sun is reduced to 24 hours a day. Therefore, there is a certain" jet lag "every day in" Pingtai Sun "and" True Sun "every day. Secondly, there is an inclination between the earth's orbital surface and the equatorial surface. This inclination has caused changes in spring, summer, autumn and winter. The average value of this inclination is 23 ° 26 ′, which is the same as the latitude value of the North Tropic.

Text/Guangzhou Daily · Xinhua City Reporter: Yecas Correspondent: He Yongjie Title Picture/Guangzhou Daily · Xinhua City Reporter: Chen Youzi Guangzhou Daily · Xinhua City Editor: Wu Yizhen

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