In return for everything Nova had done for her over the years, Cassiopiea decided to show him the wonders of space that he had been missing his entire life. However, while Nova originally came from space, he has spent his entire life on this planet, so Cass helped him train his body to regain the ability to survive in space.
Eventually, Cass was able to take him out of the planet's atmosphere, where they witnessed a beautiful celestial alignment unobstructed; a V formation, causing one of the planets in the system to eclipse the sun on one side, while forming a line of planets on the other from their perspective.
This happening the day that Nova was able to venture fully out of the planet for the first time, with Cassiopiea by his side, felt like a poetic cosmic sign that they eagerly embraced.