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A mysterious figure eight is called "analemma", she tracks the movement of the sun across the sky during the year. In general, the measurement of time - it is not always the measurement of moving forward, as we all think. Our modern calendar and the clock is none other than the types of compromise: we are in a constant battle for the synchronization of these devices with the heavens.
Throughout the history of mankind daily for a time determined by the movement of the sun. Noon is when the Sun reaches its highest point above the local horizon, crossing the north or south meridian. The problem is that the passage of the sun across the sky does not always correspond to the time of one revolution of the Earth around the star. That is, it is not the same as 24 hours. In October, the sun reaches its highest point above the horizon for 16 minutes early in February at 12 minutes later.
And why is that annoying universe does not want to remain constant?



And there is such a discrepancy due to two important factors: because of the elliptical orbit of the Earth and thanks to a certain angle at which the axis of the planet is inclined to the ecliptic plane. Of these two factors, the primary role is played by the axial tilt of the planet, and the ellipticity of the orbit is in the background. If the Earth's orbit is a perfect circle, and its axis would always be strictly perpendicular to the plane of the orbit, would be observed no seasonal differences in time. That's just not one of the planets known to science is not in such ideal conditions.
As the Earth moves around the sun in an ellipse, the orbital velocity changes. The speed of movement around the sun is maximum in January, and the slowest Earth moves in its orbit in July. Here on this motion animation is compared to an ellipse and circular motion.
And one day the earth (which moves in a circle) took a little distance and observer it looks at the sun. Earth B (moving in an ellipse) passed away a little more around the sun. But due to the fact that its orbital speed is more, she did not have time to fully turn around. This leads to the fact that we seem to you that the sun in the sky is a little further east than yesterday at the same time.
Every day difference will accumulate, and the Sun will move across the sky more and more to the east. Next, moving in an ellipse, the Earth will reach its "summer" of orbital position and its movement will be slow. Then the sun in the sky starts to move a little to the west.
In the end, it turns out that if the Earth's axis was not tilted, instead Eight sun would draw the line.
Now let's mentally inclined axis of the Earth. We are sitting at the equator, it will look as if the whole sky with the sun moved around the earth down (winter in the northern hemisphere) or up (in the summer in the northern hemisphere). Southern Hemisphere everything will be vice versa.



This photo was taken in Greece (ie, in the northern hemisphere). The lowest part of the analemma photographed in late December, and the highest - in June.



Tilt of Earth's axis we owe season. In the summer the sun rises high in the sky and more time to warm up the air and the ground. In winter, the sun is setting faster, the rays are reflected from the surface of the atmosphere, the temperature drops.
If earth's orbit was circular, but the axis of rotation of the planet was still inclined to the orbital plane is in these conditions of observation, the Sun on the celestial sphere will move along the line to the north or south of the celestial equator with respect to the range of 230 to 45. w. 230, 45 S In this case, it will be strictly repeating its trajectory by moving as one, and in the other direction.

Variable-speed motion of the Earth in its orbit appears uneven movement of the sun along the ecliptic in the sky (see equation of time). Therefore the sun to choose the moment of observation or does not reach, or pass some particular point, and the line turns into a figure similar to the eight.
Singular point in which the Sun appears twice a year, is located at the junction of the upper and lower part of the Group of Eight - the analemma. This time is in the middle of April and the very end of August each year. Time delay in the arrival of the Sun "singularity" is different on different days, but can be up to 14 minutes 19 seconds, and the lead time - 16 minutes 30 seconds. This means that at least the angular width of the sky analemmas 7, 7 degrees.
The shape of the analemma affect existing between some important calendar dates shift. Earth passes the perihelion on January 2. At this time, the velocity of the Sun on the ecliptic on the celestial sphere is maximized. Point aphelion - July 3, when the rate of motion of the sun on the ecliptic is minimal.
On the other hand, the winter solstice falls on December 22, the day of the summer solstice - June 22 (see points solstice). In the northern hemisphere these days comes a moment when the sun takes its lowest and highest position above the horizon. Odinnadtsatisutochny shift between these two summer and two winter dates precisely determines the asymmetry of the Group of Eight - the analemma.

Source: masterok.livejournal.com