Blasts from the Past: How Astronomers Measure Echoes in Space | astrobites

Figure 1: Ellipsoid of possible scatterings locations for a light echo from Eta Carinae to Earth (A. Rest et al. 2011) Last week Zachary wrote a great article about a recent spectra taken of Eta Carinae’s Great Eruption (an eruption which took place from 1838 – 1858!).  This extraordinary feat was made possible by a technique which examines light echoes from historic explosions (typically supernovae or outbursts of variable stars). The idea behind light echoes is (somewhat) simple, relying mainly on geometry, the relatively short duration of cosmic explosions, and the constant speed of light.   When an explosion occurs in space, some of the light travels directly towards us, while most travels in other directions.  If something (in our case astronomical dust) were to scatter this other light in the proper direction, it could eventually make its way to Earth as well. Now, since the speed of light is a constant, any light arriving at Earth today which originated at a given time and locat

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• Henry Zimmerman