The AIP (American Institute for Physics) has its own style manual. Click here to learn about it and download it.
The IOP (Institute of Physics) gives good guidelines for Astronomy writing. Click to access the References section in their Guidelines for Authors.
If in doubt, ask your professor.
In addition, there is the Council of Science Editor's Scientific Style and Format Guide:
Elon's Writing Center will help you understand an assignment, as well as brainstorm, draft, revise, edit & document sources.
The zotero Citation Manager is a free, easy to use tool to help you collect, organize, cite, and share your research sources.
Follow these steps to start building your own Zotero Library: