Hiểu về chu kỳ động dục. Hiểu về tác động của mùa. Biết về khung thời gian.

Given the above summary, write a detailed text in English for it.
Female cats are polyestrous, which means they go into heat many times a year.   This is in contrast to dogs, which experience a diestrus cycle, coming into heat only twice a year.   While in heat, your cat's womb will become swollen as its blood-supply increases in anticipation of a pregnancy. You will not be able to observe this, however, as there are no external signs of this process. The breeding season of feral cats is between spring and late summer. This means kittens are born away from the harshest of the winter weather, when their chances of survival would be reduced.  Artificial light can fool a pet cat into thinking it is not winter. As such, if your cat spends much time indoors, the changing of seasons will have little or no effect on her reproductive cycle.  Expect a cat that lives indoors to come into heat all year around. The reproductive cycle of a female cat is, on average, 21 days. Of these three weeks, expect her to spend as many as seven days in heat.