zenith-sweephttp://www.oed.com/dictionary/zenith-sweep_n%3Ftab%3Dmeaning_and_usezenith sweep, n.
Revised 2018

zenith sweepnoun

rare and chiefly historical.
  1. 1790–
    A linear series of observations of a region of the sky passing through the zenith (cf. sweep n. I.7).
    1. 1790
      My twenty-feet speculum was so much tarnished by zenith sweeps, in which it had been..exposed to falling dews.
      Philosophical Transactions (Royal Society) vol. 80 10
    2. 1976
      Even zenith sweeps could be made, but Herschel had to arrange a weight to work against the great motion rope.
      Journal Hist. Astronomy vol. 7 88

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

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