What does cislunar mean?
Cislunar is an adjective describing anything relating to the region of space between the Earth and the Moon — the volume bounded roughly by the Moon's orbit around our planet. The word combines the Latin prefix 'cis-', meaning 'on this side of', with 'lunar', from the Latin luna (moon); it is thus the counterpart of 'translunar', which describes trajectories or regions beyond the Moon. The term rose to prominence during the Space Race of the 1960s, when Apollo missions first carried humans across this stretch of space, and it remains central to modern aerospace vocabulary: engineers speak of cislunar orbits, cislunar navigation, and a prospective cislunar economy involving refuelling depots and communications relays. Because both the Earth and the Moon exert significant gravitational influence within it, cislunar space presents distinctive navigational challenges. The register is formal and technical, appearing mainly in scientific writing, policy documents, and space-industry journalism rather than casual conversation.
adjectiveOf or relating to the region of space between the Earth and the Moon, or to spacecraft and activities operating within that region.
- Relating to the region of space between the Earth and the Moon.
- Relating to spacecraft, orbits, or activities occurring within that Earth–Moon region.
"The agency plans to establish a permanent crewed station in cislunar space as a stepping stone for missions to Mars."
"Navigation in cislunar space requires accounting for the gravitational pull of both the Earth and the Moon."
"A growing number of commercial ventures are eyeing the cislunar economy as the next frontier for satellite servicing and refuelling."
Every Apollo mission had to cross it, but 'cislunar' only entered common usage during the Space Race — a word coined by rocket scientists, not poets.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cislunar
Cislunar derives from Latin roots: the prefix 'cis-' meaning 'on this side of' and 'luna' meaning 'moon'. It was formed on the pattern of earlier words such as 'translunar' and 'circumlunar', and entered English usage in the twentieth century alongside the development of spaceflight, becoming widespread during the Apollo era of the 1960s.
How cislunar is actually used
Predominantly used in technical, scientific, and aerospace contexts; rare in everyday speech. The term has gained currency with renewed lunar exploration programmes.
Easily confused with cislunar
Cislunar refers to the space between the Earth and the Moon, while translunar refers to travel or trajectories beyond the Moon.