Image: The parade of planets of the solar system on the ecliptic (midline of the zodiac) on December 10, 2021 at 7 p.m. Image credit: astronoo.com
The fantastic ballet of the planets
Nous savons depuis longtemps que les planètes tournent autour du Soleil et que celui-ci tourne autour de la Voie lactée.
The planets of the solar system travel in orbits that are all roughly in the same plane, which is called the ecliptic. And we, we are observers erected on one of these planets traveling with its star.
The familiar image of our solar system is usually a bird's-eye view with the Sun at the center and the planets in roughly circular orbits. But on the scale of our Galaxy, the Milky Way, our solar system with all its components is rather a flat disc on which revolve planets, asteroids, dwarf planets, comets, gas and dust.
How can we feel this journey that we make chained to the entire solar system?
To be able to feel this journey through infinite space, you have to watch a planetary parade, that is, an alignment of planets. A perfect planetary parade is an alignment of all planets in the solar system on the same side of the Sun at the same time. But this planetary parade is extremely rare (1982, 2161, 2492). Most often, two or three planets can be observed aligned in the sky. When this happens the solar system is seen edge-on. In other words, on the starry background of the Galaxy, the planets draw a line passing through the Sun lying below the horizon.
On April 26, 2022 around 6:00 a.m. SE, astronomers will have the chance to attend a planetary parade. Jupiter, Venus, Mars, Saturn and the Moon will appear simultaneously in a small sector of the sky. Another alignment will take place on June 25, 2022 around 5 a.m. towards the East.
The most disturbing thing is that we are not outside observers but we are also on this plane that we can see and feel in the night sky from our garden. The plane of the ecliptic can be identified thanks to the alignments of planets that are observed quite often. This alignment is not perfect because the planets' relatively inclined orbital planes are not perfectly on the ecliptic.
The ecliptic on which we are with the other planets can be drawn in our imagination.
For this, we must look at the quarter Moon in the night sky which tells us where the Sun is. We can also look at Venus after sunset which also tells us where the Sun is.
We are therefore somewhere on this plane with the other planets but we do not feel it because we are vertically placed on the surface of the Earth whose axis is tilted. But if we tilt the image of the sky until the line is horizontal, we realize that we are on the same plane with the whole solar system.
At that moment, a deep sensation grips us because we feel that on this flat disc our solar system plunges into the darkness of an infinite space. Without feeling anything, the Earth transports us around the Sun while rotating on itself around its axis. This movement combined with that of the other planets and that of the Sun which orbits around the Milky Way composes a dizzying global movement. Like leaves swirling in the wind, the planets all draw spirals together and take part in a fantastic cosmic ballet!
Indeed the Earth propels us at 30 km/s around the Sun which splits space at 230 km/s around the Milky Way which rushes at 630 km/s towards an immense void called the Great Attractor.
NB: The ecliptic is the plane of the Earth's orbit around the Sun. From the point of view of an observer on Earth, the movement of the Sun around the celestial sphere traces this reference plane against a background of stars. Thus, the apparent position of the Sun takes a year to make a complete turn of the ecliptic (about 1° towards the East each day). Because Earth's axis of rotation is not perpendicular to its orbital plane, Earth's equatorial plane is not coplanar with the ecliptic plane, but is inclined relative to it by an angle of approximately 23.4° (obliquity of the ecliptic). The planets of the Solar System have an orbit that is very slightly inclined relative to the plane of the ecliptic. The zodiac is on either side of the ecliptic plane.