Why does a married Jewish woman have to cover her hair ?

B"H

After doing some research on the subject why a married Jewish woman has to cover her hair, some new questions came up. Especially concerning the headcovers of widows and divorcees. At that moment I realized that there is so much more to the subject and that I haven't finished all my research. Meaning, I will continue and dig out some more opinions.
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The headcover of married Jewish women is mentioned in the Torah (Bereshit - Genesis, Parashat Chayei Sarah, 24:65). Rivka (Rebekka) is meeting Yitzchak for the first time and is covering her head. Furthermore, the headcover is mentioned in Deuteronomy (Devarim, 5:18) where we find the description of the Sotah process in the Temple. A Sotah is a married woman who is suspected by her husband of having a relationship with another man. It says that the Cohen (Priest) took off her hair cover before starting the procedure with the bitter waters.

The Talmud Tractate Ketubot 72a is giving a list of different sins of a wife where the husband can give her the Get right away (can divorce his wife). In this case, he doesn't need to pay the sum stipulated in the marriage contract (Ketubah).

- When a woman is going out to the marketplace with her hair uncovered.

Further reasons are:
- When she is cursing and yelling at her children and the neighbours hear her loud voice.
- In case, the wife is lying at her husband and letting him believe that she doesn't have her period and is "clean". The truth, however, is that she is still in her unclean days.
- When a married woman doesn't take Challah from a dough.
- When she doesn't keep her oaths and vows.

The Torah in Devarim 5:18 forbids a married woman to go to the marketplace with her hair uncovered.

But what does "going out to the marketplace" mean ? Is this only valid for going to the market ?

The Talmud explains that "market" stands for "going out into public"; leaving one's home and going out into the street. Rashi, the Ritva as well as the Tosafot allow a woman walking around without her hair covered only inside her home. Nevertheless, most religious women I know (from all directions) do cover their hair at home. Only when they are alone with their husband (no kids around) they uncover their hair.

The Mishna in Ketubot 72 teaches that a woman not covering her hair acts against the Law of Moshe. Such a woman is immodest. The Chazon Ish commented that such an act would lead to prostitution. In fact there is a suspicion that a married woman without a headcover may attract another man. Giving him the impression that she is single.

The Rambam (Maimonides, 1135 - 1214) referes to the subject in his "Mischna Thora - Hilchot Ischut 24:11". A married woman cannot go out into public without her hair covered.

The "Shulchan Aruch - Code of Jewish Law" (Even Ezer - Hilchot Ischut 21:2) lists the same rulings.

Some people may ask if a convert to Judaism is obligated to keep the same Halachot once she is married to a Jew. After her Giur (conversion).
Yes, she is obligated to cover her hair once she is getting married.

How about a convert to Judaism who was married in her "former" life and then got divorced before she became Jewish ?
She doesn't need to wear a headcover when she was married in her former life. With the conversion to Judaism, the woman is entering a new life and marriages from her past don't count.

There is an opinion, it may be a Halacha, that a married woman should only pray with her hair covered !