Will the Planets Ever Line up?

Because of the orientation and tilt of their orbits, the eight major planets of the Solar System can never come into perfect alignment. The last time they appeared even in the same part of the sky was over 1,000 years ago, in the year AD 949, and they won't manage it again until 6 May 2492.

How often do all the planets line up?

So, on average, the three inner planets line up every 39.6 years. The chance that Mars, Jupiter, Saturn, Uranus, and Neptune will all be within this arc as well on any given pass is 1 in 100 raised to the 5th power, so on average the eight planets line up every 396 billion years.

What planets will line up?

The next one isn't until Mars, Saturn and Mercury appear close in 2026. So you need to get ready for February 25-28, 2021, when the outer gas giant planets Jupiter and Saturn are visited—from our point of view, at least—by the tiny planet Mercury.