This week there were several long filaments stretching across the surface of the Sun. These remained stable and generally held the same shapes for the entire week. Filaments are clouds of cooler gases suspended above the Sun's surface. When observed in ultraviolet light, they appear dark against the Sun. As you may already know, the SOHO EIT instrument observes the Sun in four different wavelengths of extreme UV light. Each one is actually observing ionized gases at different temperatures and different distances from the surface of the Sun. But which UV wavelength shows them off the best?

In the stylized still above (taken on January 29, 2006), you see partial images from each instrument taken at almost the same time to suggest the kind of comparison that can be made. In the video, we show the full disk image from each instrument as one fades into another. The answer to the question of which is best is perhaps a matter of opinion. But it's nice to know that we have a range of wavelengths to observe with and that different features of the Sun are better seen in some than in others.