F Corona - Ef Corona

Japanese: Ｆコロナ - えふころな

…The intensity of the scattered light suggested that the corona was a dilute gas containing about ¹⁰⁸ free electrons per cm3. The light of the outer corona also includes a portion that is produced when fine dust between the Sun and the Earth scatters sunlight, and this is sometimes called the F corona. The inner corona also emits emission lines (called the E corona), but these lines could not be identified with the spectra of any substances on Earth, and at first it was thought that they were emission lines from elements unique to the Sun that do not exist on Earth. However, in the 1930s, it was discovered that these were from ions such as iron and calcium that had been highly ionized 9 to 13 times, and the surprising fact that the corona has a high temperature of 1 to 2 million K was discovered. …

From [The Sun]

...Its spectrum is exactly the spectrum of the photosphere, and many Fraunhofer lines can be seen. This is called the F corona. It is a kind of false corona. ...

*Some of the terminology explanations that mention "F Corona" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…散乱光の強さからコロナは1cm3当り10⁸個程度の自由電子を含む希薄な気体であることが示唆された。また，外部コロナの光は太陽･地球間の細かい塵が太陽光を散乱して生ずる部分を含んでおり，これをFコロナと呼ぶことがある。内部コロナは輝線スペクトルも放射している(これをEコロナという)が，これらのスペクトルはいかなる地球上の物質のスペクトルにも同定できず，初めは地上に存在しない太陽固有の元素からの輝線ではないかと考えられたが，1930年代に至って，これらは9～13回電離という高階電離をした鉄やカルシウムなどのイオンからのものと判明し，コロナは100万～200万Kという高い温度をもっているという驚くべき事実がわかった。…