The Solar and Heliospheric Observatory (SOHO) launched on Dec. 2, 1995. The spacecraft was designed to last two years. By the skin of its robotic teeth, it turns eight today. Astronomers hope it lasts half again as long, because there is no replacement.

These are two of many images taken by SOHO and used by scientists to dissect the Sun and learn about its patterns and innerworkings. The images are also used by space weather forecasters to predict solar storms that can punish Earth's protective magnetic field.

The forecasters say SOHO is, for now, one-of-a-kind. A successor won't launch until at least 2008. Meanwhile, mission managers have over the years saved the craft from three separate grave situations.

This comparison shows how much solar activity can fluctuate. The left image was taken about two years prior to the peak in an 11-year cycle of solar activity. The right image was taken amid the peak. It displays a host of active regions, where magnetic loops, solar flares and stormy coronal mass ejections originate. The image is blue because it was taken in a specific wavelength to highlight certain emissions.

To mark the spacecraft's achievements, SOHO managers recently conducted an online poll, in which the public chose 10 favorite images from the project. SOHO is a project of cooperation between NASA and the European Space Agency.

-- Robert Roy Britt

Credit: SOHO/NASA/ESA