Sun movement on the ecliptic

US, WASHINGTON (ORDO NEWS) — Suppose that we can stop the Earth’s rotation and observe only the displacement of the Sun relative to the stars. Systematically observing at the same evening time the position of bright stars and constellations in the western part of the sky, one should make sure that with each passing day the constellations come earlier and earlier, i.e. moving towards the sun.

Thus, for constellations, those constellations into which the Sun enters disappear, and vice versa, in the morning those from which the Sun descends become visible. These constellations are rising earlier in the eastern sky.

But the Sun moves not only in the plane of the celestial equator (right ascension – alfa changes), but also in the perpendicular direction (declination – delta changes). This can be seen by observing the height of the Sun at noon at different times of the year.

Stars with constant declination always culminate at the same altitude, while the sun rises high above the horizon in the summer at noon and low in the winter, which affects the length of the day and the amount of heat received. Therefore, in the summer the sun deviates from the plane of the celestial equator in one direction, to the north pole, and in the summer, to the other, to the south pole.

Exactly on the equatorial plane, the Sun is on the days of the autumn and spring equinoxes, when the day is equal to the length of the night. Measurements by the simplest goniometric devices or by the shadow of the gnomon (vertical pole) can determine the height of the Sun at noon in the summer – hs, and also in winter – hw. From the relationship of the astronomical coordinate system with the latitude of the terrain, it is known that the height of the star in the upper climax h is:

h = 90 – fi + delta,

where: fi is the latitude of the place, delta is the declination, the angular distance of the star from the celestial equator.

Since the latitude of the terrain does not change, it follows from changes in the height of the Sun that its declination is changing. The latitude of the terrain for approximately this locality can be determined by the geographical map (for Rostov 47 ° 13 “), then by measuring the height h it can be found that in summer the maximum distance from the celestial equator is + 23.5 °, and in winter it is -23.5 °. It can also be established that the Sun is on the celestial equator on March 21 and September 23, these days the declination of the Sun is 0 °.

Thus, on the star map you can draw the annual path of the Sun relative to the stars, which is a large circle inclined to the equator at an angle of 23.5 °, called the ecliptic. The constellations through which the ecliptic passes are called the zodiac. Currently, 12 such constellations have been identified (Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius) and it is believed that for a month the Sun is in each such constellation, approximately 20- x numbers moving from one constellation to another. It follows that the zodiac constellation, in which the Sun is currently located, cannot be observed, since it leaves and sets with the bright disk of the Sun, but on the other hand, the opposite constellations in which the Sun was 6 months ago are well observed.

Distinguish well-observed winter zodiac constellations such as Taurus, Gemini, Cancer, Leo and summer – Libra, Scorpio, Sagittarius, Capricorn. It should be remembered that the annual movement of the Sun relative to the stars is in fact the result of the motion of the Earth around the Sun.


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