and Plages

Prominences and plages are structures that occur above the photosphere of the Sun. Plages are bright cloud-like features found around sunspots that represent regions of higher temperature and density within the chromosphere. Prominences are features that may reach high into the corona, often as graceful loops that may hang suspended for many days.

Solar Prominences

The right image shows an eruptive prominence recorded by SOHO on June 14, 1999 (Ref). South is up in this image, which is recorded in the extreme UV part of the spectrum in the light of ionized helium atoms.

The left image below shows a prominence on the edge of the Sun photographed in H-alpha light by the Big Bear Solar Observatory at 16:17 UT on October 3rd, 1996 (Ref). The right image below shows a total solar eclipse, with several prominences in red on the limb of the Sun. The bright red color of prominences is associated with strong emission of Balmer H-alpha radiation.

Prominence on the solar limb. Prominences visible during a total solar eclipse.

Quiescent prominences are extremely stable features and remain suspended in the corona where they slowly evolve and become more elongated over the course of several solar rotations (a timescale of a few months). The loops in the prominence shown in the following image are larger than the Earth, which would easily fit under them.

A large solar prominence (Ref)

Prominences can also appear as eruptive phenomena, with the highest velocities observed as fast as 1300 km/second, and have been observed to reach heights of 1 million kilometers above the photosphere.

Prominences and Magnetic Fields

Prominences are usually associated with regions of sunspot activity, and are clearly associated with the Sun's magnetic field. They tend to lie on the boundary of regions having opposite magnetic polarity. The streaming arches and their stability for days at a time are associated with magnetic forces acting on the charged particles in the loops. It is thought that the violently eruptive prominences that are sometimes observed are associated with corresponding sudden changes in the magnetic field of the Sun.

Plage clouds

Solar Plages

Plages are particularly visible when photographed through filters passing the spectral light of hydrogen or calcium. The adjacent image shows plages near a sunspot (the white cloud-like feature) as imaged by the Big Bear Solar Observatory (Ref).