Upper panel: SOHO LASCO observations of a CME erupting from the Sun’s western hemisphere, with exposure times at 00:50, 01:27, and 01:50 UT. The CME reached a speed of 2700 km s⁻¹ at 18 R_⊙, and the associated interplanetary shock passed Earth around 04:15 UT on 23 April 2002, about 51 h after CME lift-off. Lower panel: ACE observations of high-energy oxygen nuclei showing an increase in intensity of nearly five orders of magnitude beginning shortly after the CME lift-off. We note that, while the CME images are all taken near intensity onset, the ACE intensities remained elevated for days, long after the shock had passed the Earth (from Müller & Marsden 2013, adapted from Emslie et al. 2004).