To cite earthtide in publications use:

  Kennel J, Parker B (2024). _earthtide: Parallel Implementation of
  'ETERNA 3.40' for Prediction and Analysis of Earth Tides_.
  doi:10.5281/zenodo.2673048 <https://doi.org/10.5281/zenodo.2673048>,
  R package version 0.1.5, <https://github.com/jkennel/earthtide>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {{earthtide}: Parallel Implementation of 'ETERNA 3.40' for
                  Prediction and Analysis of Earth Tides},
    author = {Jonathan Kennel and Beth Parker},
    year = {2024},
    note = {R package version 0.1.5},
    doi = {10.5281/zenodo.2673048},
    url = {https://github.com/jkennel/earthtide},
  }