I notice that there might be lack of Islamic knowledge in depth books being written by the natives in the English speaking countries like the US, the UK, Australia, so here is some glance to them. Hope they help you to understand and hope you don't mind with a way long post
The limit of Aurat in Islam
Hadith :
narrated by Abu said al-Khudri r.a, it is reported that Rasulullah s.a.w bersabda:"A man can't see the hidden parts of another man, and so do a woman can't see the hidden parts of another woman. A man can be in a blanket with another man without shirts but a woman can not be in a blanket with another woman in a blanket without shirts."
Explanation:
Clothes is among the necessity for human. Physically, clothes protecting human's skin, but spiritually it is the symbol of dignity and nobility. The Islamic way of Life defines that Aurat (certain body parts) is an obligatory to be hidden and should be respected from being seen.
According to the majority of Muslim scholars, it is obligatory for men and women to keep their Aurat whether in prayers or outside the prayers. In the whole, the four madzhabs of Islamic jurispundence which are the Hanafi, Maliki, Syafi'ie, and Hanbali have specifically fixing that the parts that should be hidden by men is from their belly-button and their knees while the women should hide their whole body except their face and two palms according to the strong proof from Quranic verse and Sunnah.
Why men and women should hide their mentioned body parts?
In discussing this question about the manner of attire and its relation with sexual crimes, sexual crimes is seen as the act that obviously violates the equality rule in Islam, so the attire code should be closely obeyed by men and women in Islam.
The solution for the interaction between men and women must return back to the practices with understanding based from the valid basis of Islam.
The basis are:
1. The relation among human between men and women must be based from the basis of brotherhood, full of respect, and helping each other toward faith and fear (love) of G-d.
2. Moral responsibility is both on the shoulder of men and women in a community. The proof is in the verse 30 - 31 Surah an-Nur with a tight emphasize on verse 30 for a faithful man as it balances the emphasize that had been given to women. Men have full responsibility to prevent their desires and controlling their mind through the way taught by the prophet (pbuh).
3. The clarity about these basic matters like what is beauty and aurat, especially among women in Islam today. Aurat covers the parts of human which is related to the reproduction system.
Beauty is divided two, which is the bestial beauty and the human's beauty. The bestial beauty is focused over the parts of reproduction system. We can see that animals like goat and cow who do not have to cover their Aurat with their genitals exposed to attract the couple that will later bring copulation or intimate relation which will produce descendants. This is a survival process in animal kingdom. Who is the most beautiful will get the chance to be breed. As so, we can understand why animals like baboons are with red back, and why male peacocks are with dazzling colorful feathers.
As for human, we evaluate beauty through the view of humanity and the view of G-d. Humanly beauty is only granted to human with high and noble moral stage. The concept of Aurat had already introduced since the creation of first human, Adam which human closing reproduction parts due to the lineage system of human must be protected and managed well.
Human naturally feels embarrased when the Aurat is exposed. It is normal and natural and exist in human soul. The bestial beauty of human is changed to the humanly beauty with the elements of modesty. When will our bestial beauty shows up? During intimate relationship with valid couple in the bedroom as a survival process of human legacy.
It would not be surprising if illegal relationship or couplation will eventually happen (with consent or without consent) if there are men and women in the public exposing their bestial beauty. In that time, the behavior of a human is no difference at all with an animal.
4. Muslim women must correct their intention. They are keeping their Aurat in order to keep the importance of men's faith. The responsibility of keeping and increasing the faith is everyone's responsibility. The same thing too happen to men, when they keep their Aurah in order to help women's keeping their faith. When a man and a woman keeping their Aurat according to what had been prescribed, they should also make a niyya (intention), that they are keeping everyone's faith. Muslim women are not only wearing veil not because of guarding themselves from evil eyes of men, but also obeying the order of G-d, which of course consist lots of Wisdom and Benefits.
Aurat represent faith and fear (love) toward G-d. We Muslims are not keeping the women but shielding their dignity due to faith and fear (love) to G-d. We are not taking alcohol and do not take pork due to our faith to G-d and His prophet (pbuh).
Sometimes, we have to find scientific explanation through researches to support our faith, but there are several Liberal Thinking Muslims or others who do not agree with our "theory". An an example: the relation between Aurat and Rape cases. When we say that keeping the Aurat may decrease rape crimes, but there are also many documents and researches piled in front of us due to they do not believe in the Wisdom of G-d. By keeping their Aurat, the chance for Satans to deceive men from violate the dignity of women will not be so intense. That is among the Wisdom of G-d Who is the One responsible to protect His slaves. In the same time, the effort of increasing the faith and the fear toward the punishment from G-d and His wrath must be implanted in ones heart. Through that way, our community will be guaranteed from the violation of rights and any form of crime could be avoided.
All right, let us see
what is Aurat?
Aurat is a word from Arabic means shame or disgrace. According to Islamic Jurispundence terminological meaning, it means parts of body that must be covered or hidden from the view of certain people according to categories.
In Islam, there are few circumstances where Muslims are allowed to show their Aurat.
The Order to Cover the Aurat
As what Allah says in the meaning of Surah al-Ahzab 33:33
And stay quietly in your houses, and make not a dazzling display, like that of the former Times of Ignorance; and establish regular Prayer, and give regular Charity; and obey Allah and His Messenger. And Allah only wishes to remove all abomination from you, ye members of the Family, and to make you pure and spotless.
From the verse, we obviously can see that the order of covering the Aurat is obligatory as other orders in religion such as performing prayers, tithe, and others. Muslim woman are easily known from their veil and it prevents them from being disturbed by those who are searching for the opportunity for their lust. Other Muslim men who see them being disturbed will quickly react to protect the Muslim woman dignity. A woman who keep their Aurat too are easily known. If they simply displaying their Aurat, they are too trying to determine men disturbing them. Thus, improper things happen, slanders about their selves will arise in community.
Allah further says in the meaning of Surah al-Ahzab 33:59
O Prophet! Tell thy wives and daughters, and the believing women, that they should cast their outer garments over their persons (when abroad): that is most convenient, that they should be known (as such) and not molested. And Allah is Oft-Forgiving, Most Merciful.
Islam outlines the limit of Aurat of men and women. The basis of men's Aurat is from their belly-button down to their two knees. While for women, they are required to cover their whole body with loose clothes except for their faces and two palms. Men can always wear towel like cloth, like you see in Pharaoh's painting as long as the towel like cloth is covering from the belly-button down to two knees and as long as they don't mind. But for women, there are few differences such as:
1. Aurat while Praying
The Aurat of women while praying is their whole body except their face and two palms.
2. Aurat while Alone
The Aurat of women while they are alone, is between their belly-button down to their two knees. This means that they just have to cover the parts from their belly-button down to their knees when they are alone.
3. Aurat while with their Mahram
Basically the Aurat of women when they are with their Mahram is between their belly-button down to their knees. However, women are ordered to close the parts that could stimulate men's desire even the men are their own Mahram. This matter is to keep the manner and protecting their own dignity from improper things. That is why the long loose cloth covering the body is adviced even when a woman is with her male Mahram.
Who are the Mahram of a woman in Islam?
1. Their husband
2. Their father
3. Paternal and Maternal Grandfather
4. Father-in-Law
5. Sons
6. Grandsons and Granddaughters
7. The sons and daughters of husband, their stepson and stepdaughter. In Islam, a stepmother must treat the children of her husband as her own because they are considered as her own children.
8. Their blood brothers
9. Their nephews
10. Their nephews who are the sons of their sisters
11. All of Muslim women or those who are related to the Muslim women
12. Their servants
13. Castrated male servants
14. Little children who has no lust nor desire toward sexual attraction and still not reaching puberty. However, a woman must cover her parts to children who are still under puberty but having the lust.
Al-Quran explained this in the meaning of Surah an-Nur verse 24:31
And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (must ordinarily) appear thereof; that they should draw their veils over their bosoms and not display their beauty except to their husbands, their fathers, their husband's fathers, their sons, their husbands' sons, their brothers or their brothers' sons, or their sisters' sons, or their women, or the slaves whom their right hands possess, or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. And O ye Believers! turn ye all together towards Allah, that ye may attain Bliss (Success).
Honorable Imam Syafi'ie who is the Imam of Syafi'ie Madzhab suggested that, the ornaments in the above verse may be divided into two meanings:
1. natural ornaments such as face, cheeks, lips, mouth, nose, legs, thighs, and other parts.
2. ornaments such as make-up, clothes, ring, necklace, bangle, and etc.
Muslims are reminded to control themselves and not exceeding the limit highlighted in Quran and Sunnah including in the matter of ornaments and attire.
What are the Aurats of a woman in front of a non-Mahram (foreign men)?
They are obliged to cover their parts in front of non-Mahram as to protect their dignity from improper slanders and protecting them from evil eyes of foreign men. A woman with improper attire may attract the lust of men due to what they had seen from the exposed parts of a woman. I had experienced my friends who are also Muslim like me might say, even if the woman is totally covered with blanket too, those men with great lust will still imagining the women or making them naked in their imagination. Now, we have to question them. How does that happened? There are many places selling Porn DVD, even they are freely circulated in my country and in my varsity. Who are the actors in the Porn DVD? Aren't they both naked women and men?
A married woman too will help their husband when they fulfill the obligation where actually a husband whose wife displaying her Aurat will have to bear the burden of sin. The sins of his wife is on the husband's shoulder because it is his responsibility to guard his wife dignity. That is why women should understand the limit of Aurats when they are in front of particular persons in different circumstances.
Aurat of a Muslim woman in front of non-Muslim woman
A Muslim woman must cover her whole body except her face and two palms when she is mingling with non-Muslim women.
Prophet (pbuh) is reported by Abdullah Ben Abbas as saying: "It is not legal for a Muslim woman being seen by a Jew and a Christian." It also covers all the un-believers not only Jewish and Christians.
The Aurat of a woman with her husband
When a woman is with her husband in the place hidden from others view, Islam has made the law easy for them. There is no Aurat limit between them. The wife may wear what she please in front of her husband, so do the husband.
Mu'awiyah bin Haidah said: "I had asked the messenger of G-d (pbuh), 'O messenger of G-d, how about our Aurat, can they be seen by others?'." The prophet answered: "Keep your Aurat except in front of your wife and your servants." I asked him further: "O messenger of G-d, how about if people bathing together in the public? He answered me: "Try as hard as you can to keep your Aurat from being seen by others and also try as hard as you can not to see others'." I asked him more: "O messenger of G-d, how about if a person is showering alone?" He answered: "You should be more embarrased to G-d than others." (Narrated Hadith by Imam Ahmad and Abu Daud)
The last answer indicates that we still have to cover when we are alone because He is always seeing us no matter if there are people around or not although there is no specific rule of attire when we are showering alone. It also applies to other acts or when we are thinking of committing evil acts.