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Interesting and Helpful Terms
The Sun is active on a daily basis. During solar maximum the Sun will put on awe-inspiring displays that include solar flares,
prominences, surface granulation and surface filaments. Here is a brief overview of those terms to help you understand
what you are seeing.
Prominences
: These look like eruptions from the disk (edge) of the Sun. Prominences can be small spiky looking
details, or large cloud like detail with fine feather-like features. They are, in fact, Ionized hydrogen emissions being
projected from the limb. Prominences are anchored to the Sun's surface in the mesosphere and extend outwards
into the Sun's troposphere.
Filaments
: These are string like features on the surface of the Sun. At high resolution they take on a 3D effect due
to the cooler aspect of the filament contrasted against the bright, hotter, Sun. They are actually prominences being
viewed against the surface.
Spicules
: A spicule is a dynamic jet of about 500km diameter on the Sun. It moves upwards at about 20 km/s from
the photosphere. Father Angelo Secchi of the Vatican Observatory in Rome discovered them in 1877. The
chromosphere is entirely composed of spicules. These features can be seen as "fur" around the edge of the disk.
Plage
: This is a bright region in the chromosphere of the Sun, typically found in regions of the chromosphere near
sunspots. The plage regions map closely to the faculae in the photosphere below, but the latter have much smaller
spatial scales. Accordingly, plage occurs most visibly near a sunspot region. Faculae have a strong influence on the
solar constant, and the more readily detectable because chromospheric plage areas traditionally are used to
monitor this influence. In this context "active network" consists of plage-like brightening extending away from active
regions, as their magnetism appears to diffuse into the quiet Sun but constrained to follow the network boundaries.
Solar Flares
: A solar flare is a violent explosion in the Sun's atmosphere. Solar flares take place in the solar corona
and chromospheres, heating plasma to tens of millions of Kelvin and accelerating electron, protons, and heavier ions
to near the speed of light. They produce electromagnetic radiation across the electromagnetic spectrum at all
wavelengths from long-wave radio to the shortest wavelength gamma rays. Most flares occur in active regions
around sunspots, where intense magnetic fields emerge from the Sun's surface into the corona. Flares are powered
by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona.
Chromosphere
: The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly
10,000 kilometers deep (approximating to, if a little less than, the diameter of the Earth). The chromosphere is more
visually transparent than the photosphere. The name comes from the fact that it has a reddish color, as the visual
spectrum of the chromosphere is dominated by the deep red H-alpha spectral line of hydrogen.
