Achromosphere ("sphere of color") is the second layer of astar's atmosphere. It is located above thephotosphere and below thesolar transition region andcorona. The term usually refers to theSun's chromosphere, but not only.
In theSun's atmosphere, the chromosphere is about 3,000 to 5,000 kilometers (1,900 to 3,100 miles) in height, or a little more than 1% of the Sun's radius at maximum thickness. It possesses a homogeneous layer at the border with the photosphere. Hair-like jets ofplasma, calledspicules, rise from this homogeneous area and through the chromosphere, extending up to 10,000 km (6,200 mi) into the corona above.
The chromosphere has a usual and expected red color due toelectromagnetic emissions in theHαspectral line. Information about the chromosphere is mostly received by analysis of its given-off electromagnetic radiation.[1]
Chromospheres have also been followed onstars other than the Sun.[2] On large stars, chromospheres sometimes make up a significant proportion of the whole star. For example, the chromosphere ofsupergiant starAntares has been found to be about 2.5 times larger in thickness than the star's radius.[3]
