Planets, stars, and other solid stellar phenomena are lumped together into this category. Planets are dense balls of matter that have gravity, a core, and can sometimes support life. They do not produce their own power. Planets range in size from the small Pluto to the giant Jupiter, which could have been a star.

A star is a huge ball of gases that uses the process of fusion (covered in the Engineering course) to create energy. A star's immense gravity sometimes pulls planets, asteroids, and comets into its orbit, creating a solar system. There are two classifications of stars - by size and by luminance. In ascending order, the sizes of stars are dwarf, main sequence, giant, and supergiant. Their luminance scale is, in ascending order, red, yellow, blue, and white. Stars adopt the Bell curve - a small amount are red dwarfs, a small amount are white supergiants, but most are yellow and blue medium-sized stars. These medium-class stars are referred to as main sequence stars.

At the end of a large star's life, it uses up the remainder of its fuel in a split-second and explodes with the power of and luminance of thousands of Earth suns. This explosion, which can and does destroy solar systems, is called a supernova. Smaller stars do not go nova; they swell up to a larger size and cool down or turn into planet-sized stars called white or black dwarfs.

Galaxies are large collections of solar systems that are millions of light-years in diameter. Galaxies are classified into three types: spiral (the Milky Way) elliptical (the Andromeda galaxy), and irregular (the Magellanic cloud). Galaxies that are neither spiral nor elliptical fit into the irregular category. It is estimated that there are 100 billion galaxies in our universe.

At the edge of the Milky Way galaxy is a large energy barrier called the Galactic Barrier. In 2265, Captain Kirk and the USS Enterprise crossed this barrier, causing a mutation with one of the crew members. It is advised that ships do not cross this barrier.

Equally dangerous is the Great Barrier, an energy barrier surrounding the center of the galaxy. Captain Kirk crossed this barrier in 2285 with the Enterprise-A. What he find inside was a malevolent, but powerful, creature that attempted to commandeer the ship by posing as God. The being was destroyed, but it is unknown if others like him exist. Crossing the Great Barrier is also inadvisable.

Pulsars are the remains of stars that have not gone nova. They shine with the luminance of millions of suns and are the most distant objects known to man.

Black holes are also the remains of stars that have not gone nova, but rather done the opposite. The star has condensed into a super-dense ball of matter a few miles wide. So dense is it, though, that its gravity is immense and not even light can escape. Its existence is known, though, due to massive amounts of gamma radiation that are emitted from the black hole. Upon entering a black hole, matter is pulled apart atom by atom. No one knows what lies beyond a black hole. Scientists speculate that it is probably a gateway to another universe or dimension.

A wormhole is a passage through space, first conceived of by Earth scientist Dr. Steven Hawking. Most wormholes are unstable, their endpoints shifting constantly through space. The only stable worm hole is in the Alpha Quadrant, several hundred kilometers from Bajor. It was created by that planet's Prophets and leads to the Gamma Quadrant.