ACRONYCHAL/əˈkrɒnɪkəl/

Happening in the evening or at nightfall.

This is now principally a technical term in astronomy, being usually applied to the rising or setting of a star at the same time as the sun sets. It derives from the Greek acronikos, “nightfall”, though it is often misspelled achronychal, as though it had some connection with khronos, “time”. The equivalent word from Latin is vespertine. Acronychal is one of three terms used in reference to star risings and settings; the others are cosmical, of a star which rises or sets at sunrise, and heliacal, of a star which is first seen to rise or set at sunrise or sunset after a period when the event was invisible because it took place in daylight.

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