Composite Carrington map of the solar hemisphere centered on 90° Carrington longitude, with the IRIS mosaic of 2014-05-27 (Mg II k radiance, yellow) and, behind the IRIS limb, He II 304 Å data from STEREO A taken at 15:00 UT on May 28 (in red). The regions inside the red, green, and blue circles indicate where the incident radiation comes from as seen from an altitude of 10 000, 20 000, and 50 000 km over the limb respectively, at the position of the prominence (+ symbol).