The Tenth of Av
On the seventh of Av, the enemy entered the Holy Temple. They ate, drank, and defiled it on the rest of the seventh and continued on the eighth of Av. On the ninth of Av, they set fire to the Holy Temple.
We therefore fast on the Ninth of Av because the beginning of a catastrophe is considered to be more tragic.
The Holy Temple burned until late on the tenth of Av. Around midday, the fires began to subside. Therefore, the restrictions of the “Nine Days” do not end until midday of the Tenth of Av, the day after Tisha B’Av.
So, the fast of Tisha B’Av ends at night when the Tenth of Av begins, which is when the stars come out. But the “Nine Days” does not end then. Some aspects of mourning are still required until midday the next day (at the Halachic «noon.» Check MyZmanim for your local listings). Then the “Nine Days” end.
Until then, it is forbidden to eat meat, or drink wine, unless it is a Seudah Mitzvah (a special meal for a Bris or the Redeeming of a Firstborn son). We may not get haircuts, bathe or shower, wash our clothes, eat meat or drink wine. It is also forbidden to listen to music, dance, or go swimming. All this is forbidden until Halachic noon on the Tenth of Av.
Once true midday passes in your area, the Nine Days are over, and you may listen to music, eat meat, take a hot shower, get a haircut, go swimming, don fresh clothes, wash your clothes, and so on.
When the Tenth of Av is on an Erev Shabbos (Friday) some of the other restrictions are lifted earlier than usual, because of the need to prepare for Shabbos. Therefore, on Friday morning we may take haircuts and wash clothing, and we may take hot baths and showers. If, however, there will not be enough hot water for everyone to bathe or shower on Friday, then it is permissible to take a hot bath or shower Thursday night after the fast ends. Music and swimming are still forbidden until midday on Friday.
If Tisha B’Av is on Shabbos, the fast is held on Sunday, the Tenth of Av. In that case, the Nine Days end Monday morning. However, bathing, washing clothing and taking haircuts are permitted Sunday night after the fast ends. All the other restrictions are forbidden until Monday morning.
Of course, if a doctor insists that a sick person must do any of these things, we obey the doctor, if the doctor is not simply trying to flout Jewish Law (I have met a number of doctors like that, but I thank Hashem that most doctors I have met have not been like that.)
May we merit the coming of Moshiach and the Final Rescue from exile soon, when Tisha B’Av will become a Jewish Holiday.