The spacecraft launched in 2006 that uses twin observatories for stereoscopic views of the Sun is STEREO.
STEREO stands for Solar TErrestrial RElations Observatory. NASA launched the nearly identical STEREO-A and STEREO-B spacecraft together on October 26, 2006, aboard a Delta II rocket. Their separate orbits gradually placed them ahead of and behind Earth relative to the Sun, allowing scientists to view solar activity from different angles.
This geometry made it possible to create three-dimensional images of solar structures, including coronal mass ejections. The mission was especially valuable because a CME can look very different when viewed from the side than when viewed from Earth head-on. STEREO therefore improved estimates of a CME’s direction, speed, and likely effect on Earth.
A common mix-up is confusing STEREO with SOHO or Solar Orbiter. SOHO is a joint ESA-NASA solar observatory launched in 1995, while Solar Orbiter launched in 2020. STEREO-B later stopped communicating reliably, but STEREO-A continued returning important solar observations.