Different phases of the CME eruption on 2011 August 04 as observed by STEREO-A. (a) Base-difference image of the Sun in STEREO-A EUVI 171 Å . Location of STEREO spacecraft and Earth on 2011 August 4 shown in inset. (b) COR1 base-difference image superimposed with STEREO-A EUVI 171 Å. (c) Superimposed base-difference images of STEREO-A EUVI 171 Å , COR1, and COR2. The red arrows in panels (a) and (b) indicate the CME leading edge. The images are plotted using JHelioviewer (https://www.jhelioviewer.org/).