How online community members learn to become valuable contributors constitutes a long-standing concern of Community & Technology researchers. The literature tends to highlight participants' acceb to practice, feedback from experienced members, and relationship building. However, not all crowdsourcing environments offer participants opportunities for acceb, feedback, and relationship building (e.g., Citizen Science). We study how volunteers learn to participate in a citizen science project, Planet Hunters, through participant observation, interviews, and trace ethnography. Drawing on Sørensen's sociomaterial theories of presence, we extend the notion of situated learning to include several modes of learning. The empirical findings suggest that volunteers in citizen science engage more than one form of acceb to practice, feedback, and relationship building. Communal relations characterize only one form of learning. Equally important to their learning are authority-subject and agent-centered forms of acceb, feedback, and relationship building.