Tonight is the longest night of the year – the night of the winter solstice in the Northern Hemisphere. It is the end of the year from an astronomic point of view.
The good news is that starting tomorrow the days are going to be longer and longer until summer arrives. Technically, the solstice occurs on December 22 at 4:48 – the same hour on the whole globe, since our 24-hours division is tied to the movement of the Earth around the sun.
The solstice and also the changing seasons on the globe are caused by Earth’s tilt of 23.5 degrees. Orbiting the Sun at that angle is the reason why the two hemispheres don’t receive the same amount of sunlight at a given time.
Each hemisphere is cooler than the other for half of every year, when the Earth’s angle positions it on the opposite part than the direction of the sun. The winter solstice occurs during the night between December 21 and 22 in the Northern Hemisphere and during the night of June 21-22 in the Southern Hemisphere. This is the night when the part of the globe that is in the opposite direction from the sun reaches the most extreme angle.
The solstice has been observed by people in antiquity even before they knew that the Earth is rotating around the sun and not the other way. It is well known that more ancient civilizations had very good astronomers who were observing phenomena by only gazing at the sky for a time long enough. So even if the solstice cannot be observed by only looking at the sky tonight, as an eclipse would, if you would be studying the sky every day of the year you could probably observe that the sun’s arc has been lowering ever since the summer solstice, reach its lower point today and then start rising again, until June when it reaches its peak during the summer solstice.
This phenomenon is the most visible at the poles. These days at the North Pole the sun’s arc is so low that it seems to rise and set in the same place, somewhere at the horizon. It seems that the “sun stands still”, which is the Latin phrasing that gave the name of “solstice” to the phenomenon.
The solstice has been celebrated by many antique civilizations which built temples and monuments to commemorate it. Some of the most famous are still standing in Egypt, at Luxor and at Machu Pichu, since over 4,000 years ago.
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