terminator

astronomy

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Last updated

July 14, 2026

Quick Summary

In astronomy, a terminator is the dividing line between the illuminated and unilluminated portions of a celestial body, such as the Moon or a planet. This line marks the transition from day to night on these bodies.1

The term "terminator" originates from the Latin word "terminus," which referred to a boundary stone. This concept of a boundary or an end point is reflected in the verb "terminate," meaning to limit or set an end to something. Historically, astronomers adopted this term to describe the distinct edge where light meets darkness on planetary surfaces.2

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Moon
Large-scale features
…passes through its phases, the terminator moves slowly across the Moon’s disk, its long shadows revealing the relief of mountains and craters. At full moon the relief disappears, replaced by the contrast between lighter and darker surfaces. Though the full moon is brilliant at night, the Moon is actually a…
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…passes through its phases, the terminator moves slowly across the Moon’s disk, its long shadows revealing the relief of mountains and craters. At full moon the relief disappears, replaced by the contrast between lighter and darker surfaces. Though the full moon is brilliant at night, the Moon is actually a…
Read More