Will there ever be a time when all our solar system’s planets align?

It will take so long for an alignment of all the planets to occur that, by then, the sun might have expanded to swallow some of them, say our readers

14 June 2023

MNN37P Illustration comparing the planets of the Solar System and the Sun on the same scale. The planets are shown to scale relative to each other but their distances are not. From left to right the bodies are: the Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. — MARK GARLICK/SCIENCE PHOTO LIBRARY/Alamy

Will there ever be a time when all the planets of our solar system line up in a row, one behind the other, as seen from Earth?

Ian Christie
Melbourne, Australia

The short answer is no. The long answer is: Assuming that we don’t need this alignment to include the sun, the limiting factor is that all of the planets must align with Mercury. We will also ignore the possibility of the sun obscuring the view of some of the planets.

This gives us two chances for each orbital period of each of the other seven planets. To a first…