* Orbital Planes: The planets in our solar system don't orbit the Sun in the same plane. Their orbits are slightly tilted, making a perfect alignment impossible.
* Orbital Periods: Each planet takes a different amount of time to orbit the Sun. It's extremely rare for them to even come close to lining up.
What about "planetary alignments" we hear about?
The term "planetary alignment" is often used loosely. What people usually mean is that some planets appear close together in the sky from our perspective on Earth. This happens because of the way our perspective changes as the planets move in their orbits.
What are the closest alignments we get?
While a perfect alignment is impossible, there are times when several planets appear relatively close together in the sky. These events are still quite rare, but not as impossible as a true alignment.
So, the answer to your question is: It depends on what you mean by "align." While all the planets can't align perfectly in a straight line, some planets can appear close together in the sky from our perspective.
