For astronomy lovers, and for the general public, this January 21 will be one of those planetary alignments that is attracting the most attention
This is the alignment that is rarely recorded and is that of six planets: Mercury, Mars, Jupiter, Saturn, Uranus and Neptune, which has generated a great stir among astronomy lovers and the general public. But how rare is this type of event and how does a planetary alignment form? Here we explain it to you.
What are planetary alignments?
When we talk about a planetary alignment, we are referring to when two or more planets align in the sky, that is, they appear to be in the same direction from our perspective here on Earth
It is important to note that they will never be perfectly aligned; there is always a small separation between them, which on average does not exceed 26 degrees in the sky. To give you an idea, this distance is what 52 moons would occupy together in the sky.
An alignment is not the same as a planetary conjunction, which is when the planets appear to be very close together, but are actually further apart. Alignments, on the other hand, are when the planets appear to be at a minimum distance from each other in the sky, explained astrophysicist and science communicator Monica W. Blanco Cardenas, according to National Geographic en Espanol.
To understand how these alignments occur, it must be remembered that all the planets in the solar system orbit the Sun, but each at a different speed. Planets closer to the Sun, such as Mercury or Venus, move faster than planets further away, such as Neptune or Uranus.
When the planets reach a point in their orbits where they align in a kind of line with the Sun, this is when the alignment occurs
“Imagine an athletics track, but all the competitors are standing next to each other. Planetary alignments last a short time because, as they continue to orbit the Sun, they overtake or fall behind each other,” the specialist said.
The rarity of planetary alignments
The rarity of planetary alignments depends on how many planets are involved and how close they are to each other. Alignments of four or fewer planets are relatively frequent and can occur several times a year. But when five planets align, it is called a great alignment, and they are much less common.
One of the rarest alignments is one involving all eight planets of the solar system, and that only happens once every 396 billion years. The last time a complete alignment occurred was in December 2022, when the planets covered a 180-degree arc in the sky.
The next planetary alignments can be predicted quite accurately thanks to Kepler’s laws, which have given us a formula to understand the movement of the planets. So, although some alignments are rarer than others, we can always know when they will occur.