In July 2012, an event took place that gives us a chance to talk about several important aspects of Chandra observations involving coordination with other observatories, how they are done, and how they fit into the bigger picture of astronomical research.
Coordinated observations are those that must be done by Chandra and one or more other observatories at approximately the same time. Astronomers often want to study objects with multiple observatories because their different capabilities --- especially in detecting different regions of the electromagnetic spectrum --- can provide insight that no single observatory can do alone. The need for coordination in time comes because so many objects in space vary over time. That means that observations taken too far apart could be less valuable because the object has changed substantially in the meantime. It's often important for all observatories involved to catch the object during a particular celestial event. In the current annual cycle, Chandra's 13th , for example, about 10% of the approved observations request coordination with another observatory.