Suppose 2 planets shared the same orbit. Each of these planets is just the right distance from its star to support life. The 2 planets are at opposite ends of their orbit, equidistant from the star, the exact same size, and are tilted 23.5 degrees on their axes, (just like Earth) so that the planets have opposite seasons. (The opposite of spring is autumn or fall; the opposite of summer is winter.) 2 planets are in the same orbit, equidistant from a star, the same size, and on opposite ends of the orbit.

On the northern hemisphere of one planet, it’s summer; on the southern hemisphere of the same planet, it’s winter. But on the other planet in the same orbit, it’s summer in the southern hemisphere, and winter in the northern hemisphere. After half a year passes in their orbit, it will be vice versa! The planets practically change sides every half year! The seasons on each northern hemisphere are opposite to each other, and the same is true for the southern hemispheres; however, the northern hemisphere of one planet is in the same season as the southern hemisphere of the other planet. Also, the southern hemisphere of the same planet is in the same season as the northern hemisphere of the other! Considering the solstices & equinoxes, this fact will remain true through out the year for both planets.

What if there were 4 planets? 2 of them could be in the equinoxes, and the other 2 could be in the solstices! If there were 3 planets, well it would be more complicated with an odd number of planets in the same orbit. The 3 planets would be a third of a year apart. If there were more than 4, the planets would be 1/x of a year apart from each other; x is the number of planets in the same orbit.

There can’t be too many planets of the same size in the same orbit, otherwise they would crash into each other! And then, whoa Nellie! The maximum number of planets an orbit can have depends on the average or constant size of the planets, and their distance from the star, as well as their gravities.