Can the 8 Planets in the Solar System Align?

As the planets in the solar system orbit the Sun, sometimes several planets appear to align in the sky. However, have all eight planets in the solar system ever truly aligned?

Alignment of the Planets

The answer to this question depends on the definition of "alignment" for the planets in the solar system. The first thing to note is that the orbits of the planets have different inclinations relative to the solar equator. According to Arthur Kosowsky, an astrophysics expert at the University of Pittsburgh, when planets appear to line up in the sky, in reality, they are unlikely to be in a straight line in 3D space.

Similarly, Nikhita Madhanpall, an astrophysics expert at the University of Wits, South Africa, states that the concept of planetary alignment is more about the visual appearance from the perspective of humans on Earth rather than physical alignment in outer space.

For example, planetary conjunction is when two or more planets appear close together from the perspective of Earth. It's important to note that the planets never actually get close to each other. Even when two planets appear aligned with Earth, their distance from each other is still vast in outer space.

However, Wayne Barkhouse, an astrophysics expert at the University of North Dakota, explains that the definition of how closely aligned the planets appear is still not clearly defined. It would involve an "angular separation," which is how astronomers measure the actual distance between two objects in the sky.

In the book Mathematical Astronomy Morsels (Willmann-Bell: 1997), Jean Meeus, a meteorology and amateur astronomy expert, calculated that the three innermost planets, Mercury, Venus, and Earth, line up on average at a distance of 3.6 degrees every 39.6 years.

Aligning more planets would take a long time. According to Meeus, all eight planets will line up at a distance of 3.6 degrees, for example, every 396 billion years. This means it has never happened and will not happen because the Sun will turn into a white dwarf in about 6 billion years from now.

Another possibility is that the eight planets will align at a distance of 1 degree from the sky. According to Meeus, this will happen on average every 13.4 trillion years. For comparison, the universe is currently about 13.8 billion years old.

Then, if the eight planets are considered aligned when they are in the same plane of the sky with a width of 180 degrees, this phenomenon will occur on May 6, 2492, according to Christopher Baird, a physics professor at West Texas A&M University.

Madhanpall notes that planetary alignment almost has no significant physical impact on Earth. The only impact on life on Earth during alignment is the beautiful sight seen in the sky.