What to see when we image the Sun in Ca K line?
- Plages or Chromospheric Faculae : Most of us are familiar with photospheric faculae which can normally only be observed towards the edge of the solar disc in white light when it is possible to view a higher region in the photosphere. These bright mottles can be up to 50,000km long and are caused by underlying magnetic fields. They are often a good predictor of future active region development and can also remain long after an active region has dissipated. The average lifetime of faculae is about 90 days and they are around several hundred degrees Kelvin hotter than the surroundings (therefore appear bright).Chromospheric faculae can be observed anywhere on the solar disc and they are an extension of the photospheric faculae into the chromosphere, details of this link are still not fully understood. Areas of very dense magnetically bright faculae or plage occur in active regions and are a good predictor of the occurrence of future sunspot formation (Evre, S. 1999). Polar faculae are short lived and only observed just before and around the solar minimum.
- Supergranulation Cells- Chromospheric Network Structure: in the quiet sun most of the chromosphere seen in Ca II K appears like a bright network pattern of irregularly shaped circles. The size of these cells is around 30,000-35,000 km in size and their average lifespan is around 20 hours. (Bhatnager, A. 2005). This is a pattern of weaker magnetic fields (the quiet network) where the magnetic elements are mixed in polarity. These are also called the intranetwork fields and the brighter edges can also be called faculae. The supergranulation cells are large scale convective horizontal flow, where material flows outwards from the centre and downward flow has been observed at the boundaries. The flow carries both polarities to the boundaries (Zirin H. 1988 p126).
- Bright rings around sunspots
- Sunspots
- K-Grains or bright points: K grains are 'intranetwork bright points' found in the quiet sun. Intranetwork bright points, cell flashes or cell grains, originate exclusively within cell interiors in quiet areas of the solar surface. These are observed almost exclusively in the Calcium H (396.85nm) and K lines (Rutten et al. 1991). They are intermittent localised brightenings which last less than a minute and often re-appear a few times at 2-4 min intervals at about the same place, and frequently occur in pairs. In Figure 2, the labelled brightenings are an example only. These bright points are tiny and good resolution is needed to observe these features. To identify them definitively, a time lapse study would need to be embarked upon and the brightenings studied to assess whether they follow the pattern of re-emergence and disappearance, again another good area for amateur study. It has been observed that these K grains do seem to correspond with G-band brightpoints observed in the intergranular lanes in the photosphere (Lite et al. 1998).
- Filaments
- Prominences
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