The first time of the day that has halachic significance is known as " amud hashachar" or "alot hashachar" (dawn). In a case of extenuating circumstances, one may begin reciting Shema and praying the Amidah from the time of amud hashachar, but under normal conditions it is prohibited. The Acharonim disagree whether amud hashachar is the time when the first glimmer of light appears in the east (Magen Avraham, Pri Megadim), or slightly afterwards, when that first light spreads out somewhat upon the eastern sky (Eliyah Rabbah, Gra).
After amud hashachar, the time called " misheyakir" arrives. This is when enough light has already spread over the earth so that a person can recognize a friend, whom he is not accustomed to meeting, from a distance of four amot. At that time it is also possible to distinguish between techelet (a shade of skylike blue) and white. According to most poskim, l’chatchilah one may recite Keriat Shema then, but the time to recite the Amidah l’chatchilah has not yet arrived.
" Netz hachamah" is sunrise, when the first part of the sun is visible. At that moment, the time to recite the Amidah l'chatchilah begins. One who recites Keriat Shema right before sunrise and prays the Amidah immediately with netz hachamah is known to be praying " vatikin," greatly praised by the Chachamim.
All of the mitzvot performed during the day, such as brit milah, begin at sunrise, since the time of day is defined by the sun. However, b’dieved, if they are performed from amud hashachar their obligations are fulfilled because, from a certain standpoint, the day begins even from the first glimmer of light (Megillah 20a).
2.Calculation of the Morning Times
According to many, the time difference between amud hashachar and netz hachamah in Israel is the time it takes to walk a distance of four mil, which is approximately 72 minutes. This means that in the months of Nisan or Tishrei, 72 minutes pass from the time the east lights up until the time the sun rises.
It is important to understand that the calculation of this time changes according to the seasons of the year. During the days of Nisan and Tishrei (beginning March 5 th and October 5 th), the duration of the sun’s ascent is shortest, and the sun rises 72 minutes after amud hashachar. However, during the winter, for reasons which cannot be outlined here, the duration of the sun’s ascent continues to lengthen until, at the height of winter (December 22 nd), 78 minutes pass from amud hashachar until netz hachamah. In the summer, the time continues to extend even longer until, at its height (June 22 nd), 88 minutes pass from amud hashachar until netz hachamah. In order to determine the precise time of amud hashachar according to this method, one must calculate the time that the sun will reach 16.1 degrees below the horizon every day – and that is the time of amud hashachar.
These calculations are based on the opinion that amud hashachar begins when the eastern sky is slightly illuminated. However, according to the opinion that amud hashachar starts when the first light in the east emerges, indeed its time is earlier, when the sun reaches approximately 17.5 degrees below the horizon. However, so as not to encounter controversy, it is proper to act in accordance with the later opinion (16.1 degrees below the horizon). Only when the sky in the east is slightly illuminated does the time of amud hashachar arrive, and from then one may recite Keriat Shema and pray the Amidah in a case of extenuating circumstances. 1
An uncertainty also arises regarding the time of misheyakir. Despite the fact that the Chachamim defined this time as one when it is possible to distinguish between techelet and white, and when one can recognize a friend whom he is not used to seeing, from a distance of four amot, there is still doubt as to the accuracy of this time. In practice, it is accepted to teach that it is around 50 minutes before netz hachamah. See the note for its exact time. 2
3.The Time of Keriat Shema
The time to recite Shema in the morning is learned from the expression that appears in the Torah passage regarded the Shema, "u’vekumecha," "when you get up," meaning the time when people normally wake up. There are people who rise early, from the time of amud hashachar (approximately 72 minutes before netz),1 therefore, biblically, it is considered the time of waking and from then on one may recite Keriat Shema. The reason for this is that the words "when you get up" are written in the singular person, implying that even when only a few people arise from their sleep it is time to recite Keriat Shema. One who recites Keriat Shema before then does not fulfill his obligation, since his recital precedes the time of waking.
The Chachamim "created a fence" (asu siyag) to the mitzvah and established not to recite Keriat Shema l'chatchilah until the time when more people usually arise from their sleep, at which point there is already more light on the earth and one can recognize his friend from a distance of four amot (Shulchan Aruch 58:1). This is the time of misheyakir (approximately 50 minutes before netz in the days of Nisan).2
When a person cannot recite Keriat Shema after the time of misheyakir due to circumstances beyond his control, he may recite it from amud hashachar. Similarly, b’dieved, if one mistakenly recites Shema from the time of amud hashachar, he fulfills his obligation. However, there is a difference between these two cases. If one’s reason for reciting Shema early emanates from circumstances beyond his control, even if he must do so every day, he fulfills his obligation. But if he recites it early due to error, he fulfills his obligation only if his mistake seldom occurs, meaning not more than once a month. If he errs more often than that, the Chachamim penalize him; he has not fulfilled his obligation and he must go back and recite it again after misheyakir (Shulchan Aruch 58:3-4; Mishnah Berurah 58:19).
The time to recite Keriat Shema lasts until the conclusion of the first three hours of the day, for there are people, such as princes, who continue to sleep until the end of the first three hours. Therefore, until the end of the first three hours is still considered to be the time of "when you get up" (this is clarified further in halachot 10 and 11).
The most praiseworthy time to recite Keriat Shema is at vatikin, meaning slightly before netz hachamah. 3
4.The Time of the Amidah
Anshei Knesset HaGedolah instituted praying three prayers every day, and established their times to correspond to the Tamid offerings. The morning Tamid was brought starting from amud hashachar, and based on that, the time of praying Shacharit l'chatchilah should begin at amud hashachar. Nonetheless, the Chachamim say that it is proper to recite the Amidah after netz hachamah, as it is written (Psalms 72:5), "Yera’ucha im shamesh" ("Let them fear You from when the sun [shines]") (Berachot 9b). B’dieved, if one recites the Amidah from amud hashachar, he fulfills his obligation because he prayed at the time when the morning Tamid offering was brought (Shulchan Aruch 89:1).
The most praiseworthy time to pray follows the manner of the early chasidim (devoted ones) who prayed at vatikin, for they would recite the Amidah at netz hachamah. 4
The time to pray the Amidah lasts four hours according to Rabbi Yehudah, for that is the last time that the morning Tamid offering may be brought. Even though, in the opinion of the Chachamim, the time to offer the Tamid lasts until chatzot, the halachah follows Rabbi Yehudah, since in Masechet Eduyot, in which all the mishnayot were chosen as halachah, the opinion of Rabbi Yehudah is brought. Therefore, the time to recite Shacharit lasts until the end of the first four hours of the day (Berachot 27a). Even so, the Chachamim’s words were not rejected completely, and if four hours passed and one did not yet recite Shacharit, he may b’dieved pray until chatzot. Although his prayer does not have the value of prayer recited on time, nevertheless, it still has certain value (as clarified further in halachah 11).
^ 1.The Talmud in Pesachim 93b-94a brings the dispute concerning how much time passes from amud hashachar (dawn) until netz hachamah (sunrise). According to Ula it is approximately the amount of time it takes to walk the distance of five mil, and according to Rav Yehudah, four mil. The Rishonim disagree concerning how long it takes to walk the distance of a mil. There are those who say 18 minutes (Rambam in his commentary on Mishnah Berachot 1:1), some who say 22.5 minutes, and others who say 24 minutes (see Shulchan Aruch, Orach Chaim 459:2 and Bei’ur Halachah there). In practice, there are two main opinions: 1) 72 minutes, approximately the amount of time it takes to walk the distance of four mil (where every mil is 18 minutes). 2) Ninety minutes (where every mil is 22.5 minutes), which is what is printed in many calendars. Also see Rav Chaim Benish’s book HaZemanim BaHalachah 21:6-9.
According to the Magen Avraham and Pri Megadim, amud hashachar is the appearance of the first light in the east, and according to Eliyah Rabbah and the Gra it arrives a little later, when the eastern skies are illuminated. The Bei’ur Halachah 58:4 and section 89:1 favors the latter opinion. One should know that both opinions are talking about a very slight light visible in the east, and someone who is in a place that has electric lighting, or one who comes from an illuminated area and has constricted pupils, cannot distinguish between these changes in the east. Similarly, a person who is not accustomed to seeing amud hashachar usually cannot detect the first light in the east, nor even discern when the eastern skies are slightly illuminated.
The approach that maintains that the time from amud hashachar until netz hachamah is 72 minutes is understandable since in Jerusalem in the days of Nisan and Tishrei, the eastern skies are illuminated 72 minutes before netz. At that time, the sun is 16.1 degrees below the horizon. The rest of the year is calculated according to that same position of the sun during the days of Nisan and Tishrei, as I have written above. Still, there are those who maintain that the calculation of 72 minutes is consistent throughout the whole year and their proof is from the Gemara in Pesachim which provides a fixed measure – four mil. However, this opinion is problematic, for the determining factor is when the east becomes illuminated and not how much time has passed. The Bei’ur Halachah 261:2 s.v. "Shehu" writes similar ideas. Therefore, it must be that the time that lapses between amud hashachar and netz hachamah fluctuates according to the seasons of the year. See HaZemanim BaHalachah chapter 17, as well as chapter 16, where he explains the reasons for the differences according to the seasons.
It is worthy of mention that all these calculations pertain to Jerusalem and to all locations along the same parallel line of latitude. The closer a person gets to the north and south poles, the longer the time difference becomes between amud hashachar and netz hachamah. Even in Israel there are distinctions. In Tzfat, which is north of Jerusalem, the time difference is longer than Jerusalem by approximately a minute and a half.
Many calendars calculate amud hashachar as 90 minutes before netz in the days of Nisan and Tishrei, when the sun is 19.75 degrees beneath the horizon. Based on this calculation, in the height of the summer, amud hashachar comes out to be 112 minutes before netz. This is very problematic, because in all these times, there is no visible light in the east. According to the astronomical calculation, before the sun arrives at 18 degrees below the horizon, even people with excellent eyesight cannot notice any light, all the more so when it is 19.75 degrees beneath the horizon. Therefore, in practice it is very difficult to rely on these calendars.
However, the opinion which maintains that four mil is 90 minutes can be explained as referring to the height of summer, since then at approximately 90 minutes before netz, the east is illuminated. It is also possible to say that according to this approach, amud hashachar is the first light in the east, and is seen when the sun is approximately 17.5 degrees below the horizon. In the days of Nisan and Tishrei, it is approximately 78 minutes before netz; in the height of the winter 85 minutes before netz; and in the height of the summer, 96 minutes before netz. Perhaps 90 minutes before netz is the average time at which one can see the first light in the east. (In addition, this opinion may possibly follow the approaches which put netz a few minutes later, since it takes the mountains into consideration, see halachah 6, and then indeed 90 minutes before netz comes out to be the average time throughout the whole year. Even the approach which maintains that a mil is 24 minutes and 4 mil is 96 minutes can be explained as referring to the height of summer.)
Therefore, in summary, the law is established based on the position of the sun. There are two main approaches. The first is when the east is illuminated, when the sun is 16.1 degrees below the horizon, which comes out to be 72 minutes before netz in the days of Nisan and Tishrei. The second is from the first light, when the sun is 17.5 degrees below the horizon, which is 78 minutes before netz in the days of Nisan and Tishrei. I have chosen to write primarily according to the opinion which maintains that amud hashachar is when the eastern skies are illuminated, when the sun is 16.1 degrees below the horizon, because that is the opinion favored by the Bei’ur Halachah, and what is written by the Yechaveh Da’at 2:8, based on the Rambam and Shulchan Aruch. In addition to that, those who follow this opinion regarding the matter of Keriat Shema and the Amidah fulfill their obligation according to all, for by that time the day has certainly begun; however, the time prior to that is controversial. It is possible to accurately calculate these times anywhere with the help of Rav Eitan Tzikuni’s computer program, "Chazon Shamayim."
^ 2.In the halachic writings of the Acharonim, a number of opinions are mentioned regarding designating the time of misheyakir. The Yechaveh Da’at 2:8 writes that it is 66 minutes before netz, and Kaf HaChaim 18:18 writes 60. In Jerusalem they follow 50-55 minutes before netz, and in some places in Bnei Brak, 45 minutes before netz. In practice, many books, such as Tefillah Kehilchatah 3:4 and Ishei Yisrael 18:1, write that it is approximately 50 minutes before netz. However, as we have learned, there are differences between the seasons of the year, and it is difficult to comprehend how these opinions ignore those discrepancies. Perhaps some of the poskim who write different times do not disagree at all, but rather each calculated the time at a different season of the year. See HaZemanim BaHalachah 23:6.
According to different visual observations, some poskim acknowledged the time of misheyakir to be when the sun reaches 12 degrees below the horizon, some say 11 degrees, and others only 10 degrees. In practice , it seems that it should be calculated according to the position of the sun when it reaches 11 degrees below the horizon. This comes out to 48 minutes before netz during Nisan and Tishrei, 52.5 minutes before netz at the height of winter (December 22 nd), and 58 minutes before netz at the height of summer (June 22 nd). Indeed, most of the year it comes out to around 50 minutes. Nevertheless, it is good to postpone the time of misheyakir another five minutes, although in extenuating circumstances, one may make it five minutes earlier.
I should add that in the past, when there were no clocks and people did not wear watches, these times were surely calculated according to human eyesight, and if the day was cloudy, the time of misheyakir was delayed a bit so as to avoid uncertainty. However, now that there are clocks and watches, Shut Sho’el U’Meishiv, Third Edition, part 2, 162, writes that the times are calculated according to them.
^ 3.According to the majority of poskim, the time of Keriat Shema begins at misheyakir and lasts for three hours, but the ideal time to pray is vatikin. This is the opinion of Talmidei Rabbeinu Yonah, Tosafot, Rosh, Rashba, Tur and Shulchan Aruch 58:1. I have written above according to this opinion. However, there are additional opinions. According to Rabbeinu Chananel and Rabbeinu Tam, the time of Keriat Shema starts after netz and lasts until the end of the first three hours of the day, and in their opinion, those who pray vatikin do not practice in accordance with halachah, because they recite Keriat Shema slightly before netz. It seems though, that even according to them, in cases of extenuating circumstances, one may recite Keriat Shema before netz. (Only according to the Razah, one does not fulfill his obligation of reciting Keriat Shema before netz.) In practice, we do not take into consideration their opinions as halachah. The Rif and the Rambam maintain that the main time for Keriat Shema is vatikin, meaning slightly before netz, and if one did not recite it at vatikin, he may do so until the conclusion of the first three hours of the day. The time prior to that is valid only in extenuating circumstances. Halachot 7 and 8 of this chapter clarify how much earlier Shacharit may be recited in practice.
^ 4.See Beit Yosef 89:1 and Shulchan Aruch HaRav 89:2. In summary , there are three main opinions: 1) According to the Rambam and Rabbeinu Chananel, the essence of the institution of Shacharit is from netz until the end of four hours, and only b’dieved one may pray from amud hashachar, as ruled in Shulchan Aruch 89:1 and Mishnah Berurah 4. 2) According to the Rosh, the Gemara teaches that vatikin is the ideal time, as it says, "Yera’ucha im shamesh" ("Let them fear you from when the sun [shines]"), but the time before Netz and the four hours after it are equal, for any time that is valid for offering the Tamid is valid for praying Shacharit. 3) According to Rabbeinu Yerucham, the time to pray b’dieved is from amud hashachar until misheyakir, and from misheyakir until netz is the time to pray l’chatchilah, as well as the time after netz.