Tonight we will have a chance to see one of the astronomical events of the year, The great planetary alignment: Seven planets (all the major planets of our solar system) will be visible in the night sky. To understand why this phenomenon and discover what it is and what is not, it is convenient to keep in mind some details about the dynamics of our solar system and its history. That is, the very story of the planets that accompany ours in the orbit around the sun.
Ecliptic. The name of the phenomenon itself, Planetary alignmentindicates that it is an event in which the planets are arranged in a row. However, we must bear in mind that when we talk about this we do not talk about the planets forming a precise row in their orbital displacements as in textbooks, nothing is further from reality.
The alignment of the planets refers to the fact that, at some point, these appear aligned in the night sky, that is, it is an apparent alignment from our terrestrial point of view that occurs around an imaginary line that crosses the night sky.
This imaginary line is the ecliptic, but in reality it is much more than a line marked by the planets. And it is that most of the objects of our solar system move through it. Even the stars seem to move following the path that this brand.
From the album to the planets. Strictly, the ecliptic It is defined as the imaginary plane that contains the orbit of the earth around the Sun. That is why this imaginary line is marked by the movement of our star in a daily transit by the celestial vault.
However, due to the fact that the orbits of planets, satellites and asteroids of our solar system orbit in different planes, the ecliptic and its surroundings become the projection in the vault of the sky of an album, the disk formed by all this infinity of orbits of objects that rotate at different distances already varied speeds but practically always in similar planes.
It is no accident that almost all the subject of our solar system is presented on this album. To understand the reason, we have to go behind in time, to the formation of our solar system, to the era in which around our star there were no planets, but a Protoplanetary disc.
Return to the origins. The origin of the solar system is in a cloud of gas and matter that ended up concentrating. In doing so, Due to the conservation of angular momentumthe cloud was taking one more disk appearance, turning at the same time on itself. The center of that cloud continued to concentrate, until it reached critical mass and density for the formation of a star, the sun.
The rest of the album was orbiting around the sun, now like a ringthe so -called protoplanetary disk. The dust also began to concentrate on different points of this album also due to gravity.
Progressive clashes were giving rise to increasingly large concentrations, dust that became increasingly large rocks until planets and asteroids were formed, all still turning in the same direction in which millions of years ago revolved the protoplanetary disc and, before, the original cloud.
The movement of the Earth. There is another factor that contributes to all objects from heaven to seem to scroll in unison and it is the fact that the Earth’s rotation axis is aligned with the axis of rotation of its orbital movement. This is more or less common, although there are exceptions such as Uranus.
If we were on this planet, we would see night after night that the stars distant to us move from this to west normally, but the solar ecliptic would move very differently, a more exaggerated version of the solar movement given in the polar circles, with a seasonal cycle of days and nights. This implies that in summer, the ecliptic plane would be a circle in the celestial vault, something very different from what we perceive from Earth.
Image | NASA/JPL