Understanding telescope pointing (i.e., line of sight) is important for observing the cosmic microwave background (CMB) and astronomical objects. The Moon is a candidate astronomical source for pointing calibration. Although the visible size of the Moon (\ang;30) is larger than that of the planets, we can frequently observe the Moon once a month with a high signal-to-noise ratio. We developed a method for performing pointing calibration using observational data from the Moon. We considered the tilts of the telescope axes as well as the encoder and collimation offsets for pointing calibration. In addition, we evaluated the effects of the nonuniformity of the brightness temperature of the Moon, which is a dominant systematic error. As a result, we successfully achieved a pointing accuracy of \ang;3.3. This is one order of magnitude smaller than an angular resolution of \ang;36. This level of accuracy competes with past achievements in other ground-based CMB experiments using observational data from the planets.
@article{arxiv.2308.15749,
title = {Pointing calibration of GroundBIRD telescope using Moon observation data},
author = {Y. Sueno and J. J. A. Baselmans and A. H. M. Coppens and R. T Génova-Santos and M. Hattori and S. Honda and K. Karatsu and H. Kutsuma and K. Lee and T. Nagasaki and S. Oguri and C. Otani and M. Peel and J. Suzuki and O. Tajima and T. Tanaka and M. Tsujii and D. J. Thoen and E. Won},
journal= {arXiv preprint arXiv:2308.15749},
year = {2024}
}