★ Florent Losse’s site. Florent’s contribution in the field of double star observation and measurement by amateurs is invaluable, in particular by having developed the REDUC software. His site also proposes a very good introduction to the principles and techniques of measurements by means of CCD imaging for those who would like to delve into this domain.

★ The  Washington Double Star Catalog, at USNO

★ The Sixth Catalog of Visual Binary Stars, also at USNO

★ Journal of Double Star Observer.

★ The Pickering scale, for estimating the seeing