adjective
interstellar
in-ter-STEL-er/ˌɪntərˈstelər/
Existing, occurring, or traveling between stars.
Clouds of interstellar gas and dust lie between the stars.

Etymology
The pieces locate something between or among stars. That spatial meaning applies both to material existing in the space between stars and to travel through that space.
In context
to observe the center of the Milky Way galaxy for stars that emitted their light 30,000 years ago traveling through the gaps of interstellar space
More examples
- Interstellar travel requires crossing enormous distances.
- Astronomers study interstellar dust to learn how stars form.
- The probe sends data back from interstellar space.
Forms
interstellar
stellar adjective — Relating to stars or their light.