Solar Disk

The principal benefit of the mission is stereoscopic images of the sun. In other words, because the satellites are at different points along the Earth's orbit from the Earth itself, they can photograph parts of the sun that are not visible from the Earth. This permits NASA scientists to directly monitor the far side of the sun, instead of inferring the activity on the far side from data that can be gleaned from Earth's view of the sun. The STEREO satellites principally monitor the far side for coronal mass ejections—massive bursts of solar wind, solar plasma, and magnetic fields that are sometimes ejected into space.^[3]

Since the radiation from coronal mass ejections, or CMEs, can disrupt Earth's communications, airlines, power grids, and satellites, more accurate forecasting of CMEs has the potential to provide greater warning to operators of these services.^[3] Before STEREO, the development of the sunspots that are associated with CMEs on the far side of the sun was only possible using helioseismology, which only provides low-resolution maps of the activity on the far side of the Sun. Since the sun rotates every 25 days, detail on the far side was invisible to Earth for days at a time before STEREO. The period that the sun's far side was previously invisible was a principal reason for the STEREO mission.^[4]

STEREO program scientist Lika Guhathakurta expects "great advances" in theoretical solar physics and space weather forecasting with the advent of constant 360-degree views of the sun.^[5] STEREO's observations are already being incorporated into forecasts of solar activity for airlines, power companies, satellite operators, and others.^[6]

STEREO has also been used to discover 122 eclipsing binaries and study hundreds more variable stars.^[7] STEREO can look at the same star for up to 20 days.^[7]