zenith-distancehttp://www.oed.com/dictionary/zenith-distance_n%3Ftab%3Dmeaning_and_usezenith distance, n.
Revised 2018

zenith distancenoun

  1. 1588–
    The angular distance of a celestial object from the zenith (the complement of its altitude or angular distance from the horizon).
    1. 1588
      For if the declination be Southward, it must be subducted from the Zenithes distance: but if Northward, added.
      A. Ashley, translation of L. J. Wagenaer, Mariners Mirrour sig. B2
    2. 1658
      Get the sum and difference of half the Suns Zenith distance at the hour of six.
      J. Collins, Sector on Quadrant 243
    3. 1704
      Zenith Distance, is the Complement of the Sun, or Stars Meridian Altitude, or what the Meridian Altitude wants of 90 Degrees.
      J. Harris, Lexicon Technicum vol. I
    4. 1854
      Zenith-distances and azimuths form..a system of angles, by means of which it is easy to fix the positions of the stars with extreme precision.
      L. Tomlinson, translation of D. F. J. Arago, Popular Lectures on Astronomy 41
    5. 1934
      Corrections for refraction must be applied to all astronomical observations in order to reduce apparent zenith distance to true zenith distance.
      H. S. Jones, General Astronomy (ed. 2) ii. 26
    6. 2009
      At large zenith distances, each point-like stellar image is widened to a noticeable spectrum.
      H. W. Duerbeck in G. D. Roth, Handbook Pract. Astronomy viii. 210

Originally published as part of the entry for zenith, n. & adj.

zenith, n. & adj. was revised in June 2018.