Calcium Ions (Ca II K) in the Sun's Atmosphere
Calcium exists in small amounts in the solar atmosphere. Since atoms in the Sun's atmosphere are extremely hot, they move around very, very quickly. The atoms often collide, and such collisions can knock electrons loose from an atom. Atoms with missing (or extra!) electrons are called ions. A calcium (chemical element symbol Ca) atom that is missing one electron is called Ca II. Normal, neutral calcium is called Ca I.
Under conditions (temperatures around 10,000 kelvins) that exist in the Sun's upper photosphere and chromosphere, calcium loses 1 electron and becomes singly-ionized (Ca II). It then gives off light in the visible or near ultraviolet range at 393 nm (3,933Å). Light at this wavelength is extremely faint but when the brilliant photospheric emissions are filtered out, the Ca II K line provides important information on the large-scale magnetic field structure in the chromosphere.
On Earth, calcium is a common gray metal that is found in chalk, limestone and the shells of mollusks. It is also crucial to the functioning of living organisms. It is essential for the growth of teeth and bones, helps control blood clotting and is used in transmitting messages along the body's nervous system.