What is the earliest time in the morning when one can put on his Talit with a Beracha?
The Shulchan Aruch (18) writes that one may recite a Beracha on his Talit as early as the point referred to as "Mi'she'yakir." "Mi'she'yakir" is the first moment in the morning when there is sufficient light to recognize one's friend from 6-8 feet away.
Practically speaking, how do we determine the point of "Mi'she'yakir"?
Chacham Ovadia Yosef writes that "Mi'she'yakir" occurs one Halachic hour ("Sha'a Zemanit") before sunrise. A Halachic hour is one-twelfth of the period of sunlight on a given day. It is calculated by first determining the time from sunrise to sunset on a given day, and dividing that time-frame by twelve. In the summertime, when the sun rises very early in the morning and sets late in the evening, a Halachic hour will exceed sixty minutes, whereas in the winter months a Halachic hour will be significantly shorter than sixty minutes.
Thus, in order to determine the earliest time for wearing a Talit with a Beracha, one needs to know what time the sun rises that day, and the length of a Halachic hour on that particular day. For example, in the American Northeast, the sun rises during the month of January at approximately 7:20 AM, and a Halachic hour is roughly 50 minutes. Hence, during this time of year, the earliest time for wearing a Talit with a Beracha is in the area of 6:30 AM. Therefore, during the winter months, when the sun rises later in the morning, those who attend early prayer services must be careful not to put on their Talit with a Beracha before this point.
Chacham Ovadia does write, however, that those who put on a Talit with the Beracha earlier, from six minutes after daybreak ("Alot Ha'shachar"), have authorities on whom to rely. Nevertheless, one should preferably wait until one Halachic hour before sunrise.
In summary, one should preferably not wear a Talit with a Beracha before one Halachic hour before sunrise, but those who do so from the point of six minutes after daybreak have authorities on whom to rely.
