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From Ancient Greek νυχθήμερον (nukhthḗmeron), noun use of the neuter singular form of νυχθήμερος (nukhthḗmeros, lasting a day and night), from νύξ (núx, night) + ἡμέρα (hēméra, day).


  • (UK) IPA(key): /nɪkˈθɛm.ə.ɹɒn/, /nɪkˈθɛ.mɪ.ɹɒn/
  • (US) IPA(key): /nɪkˈθi.mə.ɹɑn/, /nɪkˈθɛməɹɑn/
  • (file)


nychthemeron (plural nychthemera or nychthemerons)

  1. A period of one day and one night, a date: in the West, this is a period of 24 consecutive hours.
    • 1715, David Gregory, The Elements of Astronomy, Physical and Geometrical, volume 2:
      It has not yet been found by Observation, whether Mercury turns upon its own Axis, ... that is, whether it has the vicissitude of Day and Night, much less what is the space of its Nychthemeron or Natural Day; but one may safely enough conjecture that it does revolve about its Axis, since the other Planets do.
    • 1839, The Foreign Quarterly Review, volume XXII, Black and Armstrong (London), page 181:
      Ideler passes over the Indians, and with good reason ; for they had not the week, and could not have had it, since they divided the nychthemeron into thirty hours, which the following out the same method would give rise to an entirely different series of planetary regents.
    • 1879, C. Edward Sachau, The Chronology of Ancient Nations: An English Version of the Arabic Text of the Athâr-ul-Bâkiya, translation of original by Muḥammad ibn Aḥmad Bīrūnī:
      Now, the Arabs assumed as the beginning of their Nychthemeron the point where the setting sun intersects the circle of the horizon. Therefore their Nychthemeron extends from the moment when the sun disappears from the horizon till his disappearance on the following day.
    • 1936, Osiris, History of Science Society, page 112:
      For the division of the nychthemeron into equal parts, we are indebted to the Sumerians. Following the fiction of the ideal year of 12 months of 30 days to each, they divided the nychthemeron into 12 danna (46), each of 30 giš (47).
    • 1998, James Evans, The History and Practice of Ancient Astronomy:
      Geminus says in his Introduction to the Phenomena (VI, 1-4) that the nychthemeron (a day and night together) is not of constant length.
    • 2000, William Wilson Hunter Sir, Sekharipuram Vaidyanatha Viswanatha, Clarisse Bader, The Indian Empire: its people, history, and products:
      The Hindus consider the day as the first, the night as the second, part of the nychthemeron. There-fore they call the former Sâvana, i.e. a day depending on the rising of the sun. Besides, they call it Manu-shyâhorâtra, i.e. a human day, because, in fact, the great mass of their people do not know of any other kind of day but this.
    • 1998, Emmanuel A. Paschos, Panagiotis Sotiroudis, The Schemata of the Stars: Byzantine Astronomy from A.D. 1300:
      The first sphere moves in each nychthemeron 0° 3′ in opposite sense to the zodiac. The second sphere moves 13° 11′ in each nychthemeron in the sequence of the signs of the zodiac.
    • 2003, William H. Moorcroft, Understanding Sleep and Dreaming, page 30:
      Another difference at this age is the distribution of sleep and wake across the nychthemeron.

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