Question on fasting
Question
Please what time of the day does a Jew START a fast? Does a Jew start fasting when the sunsets in the evening?
Answer
Shalom!
Thank you for your question.
The “minor fast” days begin at the crack of dawn, also known, as “alot hashachar.” There is a difference of opinion among the authorities as to when exactly this is. According to some this is when the sun is 17.5 degrees below the horizon while others say it is when the sun is 16.1 degrees below the horizon. The two primary opinions in this matter is that this is either 72 minutes before sunrise or 90 minutes before sunrise. Le'halach we start from 72 minutes before sunrise.
The fast ends at dark, also known as “tzeit hakochavim” which is when three “medium size” stars can be seen. According to some authorities it is when the sun is 4.8 degrees below the horizon while others say it is when the sun is 6.2 degrees below the horizon. The two primary opinions in this matter is that the fast ends 24 minutes after sunset, or, in an emergency,18 minutes after sunset.
An interesting application of the fast days start and end times is relevant to one who flies from the United States to Israel. Such a person will have a much shorter fast to observe because one is flying in the opposite direction of the sun. According to modern flight speeds, this works out to mean that every hour of flight (when flying from West to East) shortens the fast by more than half an hour. On the other hand, one who flies from Israel to the United States will have a longer fast to observe because one if flying in the same direction of the sun. Here too, every hour of flying lengthens the fast by more than half an hour. The fast ends according to the place he is flying over if in that place it has ended he may eat.
One who intends to wake up early in order to eat before the fast begins should make such a declaration before going to sleep for the night. If such a declaration was not made, one should not eat unless extremely necessary for example, the fast will be difficult or it will be hard for him to study Torah during the day. Drinking is permitted according to the Ashkenazi custom whether or not one made a declaration to wake up early in order to drink. According to the Sephardi custom drinking is like eating.
The “major” fast days, namely the rabbinic fast of Tisha B’av and the biblical fast of Yom Kippur, are 24+ hour fasts which begin just before sunset and end the next day at dark.