They just mean that some of the planets are in the same general sky region. If you look at a two-dimensional representation of the planets and their orbits on a piece of paper, you might think that all planets will eventually orbit along the same line. The fast moving inner planets can be aligned as regularly as every few months or so, while groupings of the slower outer planets – Jupiter, Saturn, Uranus, and Neptune – are far less common when they do so but last longer. Sometimes only the brightest planets line up in a row that looks like a necklace.
How often do the 7 planets align?
All eight planets in the solar system and dwarf planet Pluto lined up on one side of the sun at the same time. As a result, similar conjunctions of Venus and Jupiter occur at regular intervals of about 3 years and 3 months. About every 100 years or so, six or more planets line up and appear together in a small area of the sky. Large conjunctions between Jupiter and Saturn occur every 20 years, making the planets appear to be close to each other.
In other words, the moon’s gravitational effect, which approaches and moves away from Earth each month, is far stronger than that of planetary alignment, no matter how invented.
When was the last time that every planet aligned?
The red planet Mars, distant Uranus and Neptune, which were approaching their opposites, were well positioned for observation, as were the gas giants Jupiter and Saturn. The downside is that you’ll probably only see three of these planets, as Mercury is positioned too close to the Sun and Jupiter stays very low above the horizon in most places. The four outermost planets of Jupiter, Saturn, Uranus and Neptune will be accessible to spaceships from Earth. To see how planetary alignment might play out, I calculated the gravitational force of each planet when it was closest to Earth.
All eight planets in the solar system and dwarf planet Pluto lined up on one side of the sun at the same time.