Mincha - Calculation

QUESTION: The earliest time one may daven mincha is half an hour after midday (mincha gedola). Is this calculated as 30 standard minutes after midday, or is it based on sha’os zmaniyos. (Sha’os zmaniyos means that each hour is 1/12 of the hours of daylight.)

ANSWER: In certain areas of halacha related to tefilla, we reckon an hour based on sha’os zemaniyos. For example, krias shema in the morning must be recited by the end of the fourth hour of sha’os zemaniyos. With respect to the half hour after midday, the Mishnah Berurah (Shaar Hatziyun 233:8) is unsure whether we calculate based on sha’os zmaniyos or not. There is a strong argument to be made that the half hour is 30 standard minutes. In theory, one should be able to daven mincha immediately after midday because it is the afternoon. However, Chazal added an extra half hour to avoid mistakes. It would stand to reason that this half hour should be uniform for all times of the year (30 standard minutes). However, the Mishnah Berurah notes that the wording of the Gemara implies that we calculate the half hour based on sha’os zmaniyos. This seems to be his main opinion, since in Mishnah Berurah (233:4) he writes only to calculate based on sha’os zmaniyos. 

How does one calculate sha’os zmaniyos? The day is divided into 12 equal parts, and each part is one halachic hour. For example, if there are 9 hours of daylight, one hour of sha’os zmaniyos will be 45 minutes long. There is a disagreement among poskim how this should be calculated. According to some poskim, the hours of the day begin with sunrise and end with sunset, and this amount of time is divided into 12 parts. According to others, we calculate from dawn (alos hashachar) until stars appear (tzeis hakochavim).  

In the summer months when sha’os zmaniyos are more than 60 minutes, one should wait to daven mincha until a halachic half hour after midday. In the winter, when sha’os zmaniyos are less than 60 minutes, strictly speaking one can daven after a halachic half hour (which is less than 30 minutes), but it is proper to be strict and wait 30 minutes (see Piskei Teshuvos 233:1).

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