Down in Space Is Relative: Planes, Orbits, and the Cosmic Bearings
There isn’t a universal ‘down’ in space. The solar system lies in a flattened disk (the ecliptic) because the collapsing rotating solar nebula shaped planets to orbit in roughly the same plane. The Milky Way has its own galactic plane (tilted about 60° to the ecliptic), and the Local Group sits in a nearly perpendicular supergalactic plane (about 84.5° to the galactic plane). Orientation of these planes comes from the initial rotation of matter when clouds collapsed, so every star, planet, and galaxy can have its own plane and direction depending on where you’re looking.
