This question asks the student to determine how long it would take light emitted from a given object (a galaxy or a supernova) to reach an observer on Earth, also known as the look-back time for that object. The students are also asked to give the date an event might have occurred, as well as a projected date of knowledge of the event for an observer on Earth.
keywords: look-back time, light, time, date, Earth observer
swf file: ca_intro_lookbacktime.swf