Editing Chromosphere (section)

=== Loops ===

{{see also|Coronal loop}}

Plasma loops can be seen at the border of the solar disk in the chromosphere. They are different from [[Solar prominence|solar prominences]] because they are concentric arches with maximum temperature of the order {{Val|0.1|u=MK}} (too low to be considered coronal features). These cool-temperature loops show an intense variability: they appear and disappear in some UV lines in a time less than an hour, or they rapidly expand in 10–20 minutes. Foukal<ref>{{cite journal |author= Foukal, P.V. |title= The pressure and energy balance of the cool corona over sunspots |journal= The Astrophysical Journal |year= 1976 |volume= 210 |page= 575 |bibcode=1976ApJ...210..575F |doi=10.1086/154862 }}</ref> studied these cool loops in detail from the observations taken with the EUV spectrometer on [[Skylab]] in 1976. When the plasma temperature of these loops becomes coronal (above {{Val|1|u=MK}}), these features appear more stable and evolve over longer times.