Average motion of emerging solar active region polarities - I. Two phases of emergence H. Schunker, A. C. Birch, R. H. Cameron, D. C. Braun, L. Gizon and R. B. Burston A&A, 625 (2019) A53 Published online: 10 May 2019 DOI: 10.1051/0004-6361/201834627