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These are large, looping cur- tains of gas that can last for several days. Their arched shape follows, and is sup- ported by, magnetic field lines that loop out of the surface and then back in. Prominences can also cause material to be thrown out into the corona, to become fluctuations in the solar wind. Figure 14.10 shows one of the largest prominences ever

recorded on film.

* coronal holes. The corona does not wrap completely

around the Sun, but usually contains holes, particularly over the solar poles. Looking back to the X-ray photograph of the corona shown in figure 14.5, enormous coronal holes can clearly be seen over the poles. The survey of the solar wind performed by Ulysses has found that coronal holes are the primary source of the fast solar wind. As the Sun rotates, large coronal holes reappear every 27days or so,

creating a regular gusting in the solar wind.

* coronal mass ejections. The existence of coronal mass ejections (CME) has only been known since the early 1970s. CMEs are large, magnetically confined bubbles of plasma, containing between one and ten million million kilograms of coronal material. They expand and accelerate away from the Sun, reaching speeds up to 1000 kilometres per second. CMEs are released by solar flares and prominences, as well as some other solar events. At their slowest rate of release, one CME per week is recorded, while at peak production two

or three per day can be found.

The onrush of large volumes of fast moving plasma can have a sever