"Cosmos" airs on Sunday on Fox and is hosted by Neil deGrasse Tyson. Fox

“Cosmos” returns to Fox and in the fourth episode, “A Sky Full of Ghosts,” Neil deGrasse Tyson explores how our view of the universe is shaped by light, time and gravity. For its heroes of science segment, Sir Patrick Stewart (“Star Trek”) will be the voice of astronomer William Herschel.

Viewing the universe is not as simple as looking outward from Earth and astronomers, for example, have used gravity to observe distant galaxies. Gravitational lensing, the distortion of light caused by the gravity of an object, allows astronomers to observe galaxies of the early universe. Light from a more distant galaxy is bent by another galaxy as it travels to the observer and researchers can observe this phenomenon as arcs in a photo. A gravitational lens can also magnify a distant galaxy.

In the first “Cosmos” clip, “The Event Horizon,” Tyson explores the area around the supermassive black hole at the center of the Milky Way Galaxy, known as Sagittarius A*, and the event horizon associated with black holes, known as the “point of no return.” Black holes, and their incredible gravitational pull, also affect space-time and Tyson’s “Ship of Imagination” teases viewers about what it would be like inside one of these objects.

The “Where Are We in the Universe?” trailer examines the cosmic horizon and one’s place in the universe. According to the “Cosmos” clip, everyone is “special” since, regardless of your location in the universe, you are at its center due to perception.

The “Heroes of Science” animated segment of “Cosmos” will examine the work of the pioneering astronomer William Herschel, voiced by Patrick Stewart. Herschel discovered Uranus and was the first to understand that the night sky is full of “ghosts” because by the time the light from a distant star reaches Earth, that star is “already dead.”

“Cosmos” airs on Fox on Sundays at 9 p.m. EDT and on National Geographic on Mondays at 10 p.m. EDT.