The Hebrew wordonah, which does not occur in the Bible, literally means "time period" or "season." In the context of the Jewish laws of niddah, it usually refers to a day or a night. Each 24-hourday thus consists of two onot. The daytime onah begins at "netz hachamah" and ends at "shekiat hachamah". The night-time onah lasts from sunset until sunrise. Marital relations are forbidden on an onah when a woman anticipates her menstrual cycle. This is called an "onat perishah". The term onah can also refer tothe length of the menstrual cycle. Halachically, one assumes that the "onah beinonit", is thirty days long. The term "mitzvat onah" refers to a husband's conjugal obligations toward his wife and is also used as a halachic euphemism for marital relations. Some say: The mitzvah of onah – marital intimate relations – is defined in the Mishnah as fixed, regular times that a married couple may not be intimate together. The times for conjugal duty prescribed in the Torah are: for men of independence, every day; for laborers, twice a week; for ass-drivers, once a week; for camel-drivers, once in thirty days; for sailors, once in six months. These are the rulings of R. Eliezer. R. Joseph learnt: Her flesh implies close bodily contact, viz, that he must not treat her in the manner of the Persians who perform their conjugal duties in their clothes. This provides support for R. Huna who laid down that a husband who said, ‘I will not unless she wears her clothes and I mine’, must divorce her and give her also her ketubah. R. Yaakov Emden: One should ease his wife's mind and make her happy, prepare her and nurture her with words that make her happy so that she feels passionate towards him. According to the Rabad enumerated four permitted "kavvanot" for sexual relations with rewards in the world to come: for procreation, for welfare of the fetus, for a wife’s desire, and that a man has desire to act promiscuously and relieves that through intercourse with his wife. Yet the last one is a lesser reward, since the man should have had the strength to resist. If He does not show any strength, and has sex anytime he wants, this would not be rewarded. Maimonides and other rationalists saw sexuality and desire as an animal drive, not something for the rational man. He says: “The sense of touch which is a disgrace to us leads to indulge in eating and sensuality”, etc. There was a deep reaction to this about a generation after the Rambam. The growing movement of Kabbalah and other schools of the region had a negative reaction to this passage of Maimonides quoting Aristotle. the Nahmanides in "Iggeret Ha-kodesh" says: "But we who have the Torah and believe that God created all in his wisdom created anything inherently ugly or unseemly. If we were to say that intercourse is repulsive, then we blaspheme God who made the genitals".
