@article{ArltValliappanSchmieletal.2016,
  author    = {Arlt, Rainer and Valliappan, Senthamizh Pavai and Schmiel, C. and Spada, F.},
  title     = {Sunspot positions, areas, and group tilt angles for 1611-1631 from observations by Christoph Scheiner},
  series = {Mountain research and development},
  volume    = {595},
  journal   = {Mountain research and development},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201629000},
  pages     = {10},
  year      = {2016},
  abstract  = {Methods. In most cases, the given orientation of the ecliptic is used to set up the heliographic coordinate system for the drawings. Positions and sizes are measured manually on screen. Very early drawings have no indication of their orientation. A rotational matching using common spots of adjacent days is used in some cases, while in other cases, the assumption that images were aligned with a zenith-horizon coordinate system appeared to be the most probable.},
  language  = {en}
}