When does the second phase of the menstrual cycle begin?

The second phase of the menstrual cycle, known as the luteal phase, begins with the release of an ovum from the ovaries, a process called ovulation. This marks the transition from the follicular phase, which occurs before ovulation. During the luteal phase, the ruptured follicle transforms into the corpus luteum, which then secretes progesterone. This hormone plays a crucial role in preparing the endometrium for a potential implantation of a fertilized egg. Understanding the timing of these phases is essential, as it highlights the hormonal changes and physiological processes involved in menstruation and fertility. Thus, the identification of the onset of the luteal phase requiring ovulation to occur makes this answer accurate.