Spectral sequences of SN 2017ckj. The positions of the principal transitions from H, He and other spectral elements are highlighted by the dashed vertical lines. The ⊕ symbols mark the position of the strongest telluric absorption bands. The phase of spectra based on the estimated explosion epoch (MJD = 57837.1  ±  0.1) is given on the right-hand side. All spectra have been corrected for redshift and extinction. The last two spectra, with lower signal-to-noise ratio (S/N), have been smoothed using a Savitzky-Golay filter.