That's a fun question! While there are constellations that are only visible during specific seasons, you can't say that any two constellations are *never* in the sky at the same time.

Here's why:

* Earth's Rotation: As the Earth rotates, the entire sky appears to move across the horizon. So even if constellations are on opposite sides of the Earth, they will be visible at different times of the night.

* Seasonal Shifts: Constellations are associated with specific seasons due to the Earth's orbit around the Sun. But even during the "opposite" season, those constellations will still be visible for a short time, especially near the horizon.

Example: Let's say we're talking about Ursa Major (the Big Dipper) in the Northern Hemisphere and Orion, which is visible in winter. While Orion is prominent in the winter sky, Ursa Major is still visible in the northern sky throughout the year, just not as high in the sky.

So, to answer your question, no two constellations are *never* in the sky at the same time. They might be on opposite sides of the sky, but with the Earth's rotation and the passage of time, they will both be visible at some point.