Movement of the sun along the ecliptic

(ORDO NEWS) — Let us assume that we can stop the rotation of the Earth and observe only the displacement of the Sun relative to the stars.

By systematically observing the position of bright stars and constellations in the western part of the sky at the same evening time, one should make sure that every day the constellations set earlier and earlier, i.e. moving towards the sun.

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

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

Stars with constant declination always culminate at the same height, while the Sun rises high above the horizon at noon in summer, and passes low in winter, which affects both the length of the day and the amount of heat received.

Consequently, the Sun in summer deviates from the plane of the celestial equator in one direction, towards the north pole, and in summer – in the other direction, towards the south pole.

Exactly in the plane of the equator, the Sun is located on the days of the autumn and spring equinoxes, when the length of the day is equal to the length of the night.

By measuring the simplest goniometric devices or by the shadow of a gnomon (vertical pole), one can determine the height of the Sun at noon in summer – hs, and also in winter – hw. From the connection of astronomical coordinate systems with the latitude of the area, it is known that the height of the luminary at the upper culmination h is:

h = 90 – fi + delta,

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

Since the latitude of the area does not change, it follows from changes in the height of the Sun that its declination changes.

The latitude of the area approximately for a given settlement can be determined from a geographical map, 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 at the celestial equator on March 21 and September 23, on these days the declination of the Sun is 0 °.

Thus, on a star map, one 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 along 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 during the month the Sun is in each such constellation, approximately 20 x numbers moving from one constellation to another.

It follows that the zodiacal constellation in which the Sun is currently located cannot be observed, since it leaves and sets together with the bright disk of the Sun, but at midnight the opposite constellations are well observed, in which the Sun was 6 months ago.

There are well-observed winter zodiac constellations such as Taurus, Gemini, Cancer, Leo and summer ones – Libra, Scorpio, Sagittarius, Capricorn. It should be remembered that the yearly movement of the Sun relative to the stars is actually the result of the movement of the Earth around the Sun.


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