Is the smallest constellation in the whole day the Southern Cross?

One of the southern constellations. The smallest constellation in the whole day. The Milky Way, located between Centauri and Flies, can only be seen in several southern provinces of China. The main bright stars in the constellation form a cross, which is drawn downward from a vertical position of the cross until a point about four times the length of this vertical position is the south celestial pole. Observed at low latitudes in the northern hemisphere, the intersection of this extension line and the horizon is basically due south. Zheng He, a navigator in the 0/4th century AD/KLOC, used this constellation in his seven voyages to the Western Ocean. In Ptolemy's time in ancient Greece, it could be seen in the Mediterranean and was regarded as the foot of a centaur. Due to precession, in modern times, this part of the starry sky has moved south and can no longer be seen in most parts of the northern hemisphere. So it was not until the17th century that European astronomers took it out of Centauri as an independent constellation. The part of the Milky Way where the Southern Cross is located is the brightest part of the Milky Way. At the lower left of the cross of the Southern Cross, there is a dark dust nebula, which is like a dark cave in the Milky Way against the bright background, called "coal bag". Its area is almost as big as the cross, extending to the adjacent Centauri and Fly.

Learning point

precession of the equinoxes

Precession is the slow conical motion of the earth's axis around an axis passing through the center of the earth and perpendicular to the ecliptic plane (referring to the earth's orbital plane around the sun). The period is about 26,000 years, which is caused by the attraction of planets such as the sun and the moon to the equatorial uplift of the earth. Therefore, the vernal equinox (the point on the earth's orbit when the sun shines directly on the equator) gradually moves westward.