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Reference of Measurements in Halacha: Difference between revisions

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==Food or Drink==
==Food or Drink==
===Kezayit===
===Kezayit===
{| class="wikitable sortable"
!Opinions
!Kezayit (cm<sup>3</sup>)
|-
|Rav Mordechai Willig<ref>Rav Mordechai Willig ([http://www.yutorah.org/lectures/lecture.cfm/760487/Rabbi_Mordechai_I_Willig/How_Much_Matza_Do_You_Need_to_Eat Pesach To-Go, Nisan 5771], p. 60) is of the opinion that the size in volume of a kezayis is 22.5 cubic centimeters. His calculations are primarily based on Rav Hadar Margolin.</ref>
|22.5
|-
|Rav Chaim Noeh<ref>Rav Chaim Noeh in Shiurei Torah (3:11, pg 191, 5707) writes that for Deoritta Mitzvot one should eat 28.8cc, however, in Shiurei Tzion (p. 70, 5709) he writes that it is 27cc. Vezot HaBracha (Birur Halacha 1) explains that Rav Chaim Noeh retracted from his original ruling.</ref>
|27
|-
|Rav Moshe Feinstein<ref>Vezot HaBracha (Birur Halacha 1) quotes Haggadat Kol Dodi which quotes Rav Moshe Feinstein as saying that a [[Kezayit]] is 31.2cc.</ref>
|31.2
|-
|Chazon Ish<ref>Rav Chaim Kanievsky in Shiurin Shel Torah (p. 66) quotes the Chazon Ish that a [[Kezayit]] is 2/3 of a modern egg and an egg can possibly be up to 55cc. Therefore, Vezot HaBracha (Birur Halacha 1) writes that the Chazon Ish holds that 33.3cc is a [[Kezayit]]. The Chazon Ish's opinion of [[Kezayit]] is partially based on the opinion of the Tzlach. </ref>
|33.3
|}


#According to Ashkenazim, all sizes are measured in volume and not weight.<ref>Mishna Brurah 456:3, Vezot HaBracha (pg 6) </ref> However, according to Sephardim the actual halacha is that measures are in volume but the minhag is to follow the measures in weight. <ref>See Yalkut Yosef (Klalei [[Brachot]] pg 195-202) who discusses this at length. However, see Or Letzion (Vol. 3, Introduction) who argues that the custom to use weight is only for foods which have similar density to water, but for other foods (like Matza) one would use volume. Halacha Brurah 210:2 rules that the kezayit is measured by volume and not weight. See Otzrot Yosef 8:9. </ref>
#According to Ashkenazim, all sizes are measured in volume and not weight.<ref>Mishna Brurah 456:3, Vezot HaBracha (pg 6) </ref> However, according to Sephardim the actual halacha is that measures are in volume but the minhag is to follow the measures in weight. <ref>See Yalkut Yosef (Klalei [[Brachot]] pg 195-202) who discusses this at length. However, see Or Letzion (Vol. 3, Introduction) who argues that the custom to use weight is only for foods which have similar density to water, but for other foods (like Matza) one would use volume. Halacha Brurah 210:2 rules that the kezayit is measured by volume and not weight. See Otzrot Yosef 8:9. </ref>
#There’s a dispute in the Rishonim whether the [[Kezayit]] (olive size) is a half or third of a [[KeBaytzah]] (egg size), and regarding [[Bracha Achrona]] and Deoritta Mitzvot, the halacha follows the opinion that a [[Kezayit]] is half a KeBeytzah. <ref>*Mishna Brurah 486:1 writes that the Tosfot holds a [[Kezayit]] is half of a KeBeitzah with the shell and the Rambam holds it is a third of a KeBeitzah (see Tosfot (Yoma 80b s.v. Agav), Rambam (Eiruvin 1:9)). S”A 486 rules like Tosfot. Rav Avraham Chaim Noeh (Shiurei Torah 3:12) argues that Tosfot holds half a KeBeitzah without the shell.
#There’s a dispute in the Rishonim whether the [[Kezayit]] (olive size) is a half or third of a [[KeBaytzah]] (egg size), and regarding [[Bracha Achrona]] and Deoritta Mitzvot, the halacha follows the opinion that a [[Kezayit]] is half a KeBeytzah. <ref>*Mishna Brurah 486:1 writes that the Tosfot holds a [[Kezayit]] is half of a KeBeitzah with the shell and the Rambam holds it is a third of a KeBeitzah (see Tosfot (Yoma 80b s.v. Agav), Rambam (Eiruvin 1:9)). S”A 486 rules like Tosfot. Rav Avraham Chaim Noeh (Shiurei Torah 3:12) argues that Tosfot holds half a KeBeitzah without the shell.
*What's the halacha? Mishna Brurah 486:1 rules that for Deoritta Mitzvot and [[Bracha Achrona]], one should eat the size of half a KeBeitzah, but for Derabbanan Mitzvot, one third suffices. He adds that since one has to make a Bracha on [[maror]], one should eat half a KeBeitzah.
*What's the halacha? Mishna Brurah 486:1 rules that for Deoritta Mitzvot and [[Bracha Achrona]], one should eat the size of half a KeBeitzah, but for Derabbanan Mitzvot, one third suffices. He adds that since one has to make a Bracha on [[maror]], one should eat half a KeBeitzah.
*Chazon Ish 39:17 decided that we could be lenient like the Rambam. see below for an exact amount according to Chazon Ish</ref>
*Chazon Ish OC 39:17 decided that we could be lenient like the Rambam. See below for an exact amount according to Chazon Ish.</ref>
#According to Rav Chaim Noeh, the [[Kezayit]] for Deoritta measures (eating [[Matzah]]) and [[Bracha Achrona]] is 27cc. The Chazon Ish’s opinion is that the [[Kezayit]] is 33.3 grams (1.3 oz). <ref>*The Tzlach (Pesachim 116b) holds that the modern day eggs are half the size of those in the days of Chazal. However, Rav Noeh (Shiurei Torah Shaar 3) argues that the modern day eggs have not changed from the days of Chazal. Mishna Brurah 486:1 writes that for the mitzvah deoraitta of [[matza]], one should follow the stringent view of the Tzlach. see Rav Shlomo Wahrman (Orot Haesach 28) who explains why there is no need to say that the eggs have shrunk since the times of the Gemara. see also Maaseh Rav 74, where it says that the Gra accepted the position of the Tzlach.
#According to Rav Chaim Noeh, the [[Kezayit]] for Deoritta measures (eating [[Matzah]]) and [[Bracha Achrona]] is 27cc. The Chazon Ish’s opinion is that the [[Kezayit]] is 33.3 grams (1.3 oz). <ref>*The Tzlach (Pesachim 116b) holds that the modern day eggs are half the size of those in the days of Chazal. However, Rav Noeh (Shiurei Torah Shaar 3) argues that the modern day eggs have not changed from the days of Chazal. Mishna Brurah 486:1 writes that for the mitzvah deoraitta of [[matza]], one should follow the stringent view of the Tzlach. see Rav Shlomo Wahrman (Orot Haesach 28) who explains why there is no need to say that the eggs have shrunk since the times of the Gemara. see also Maaseh Rav 74, where it says that the Gra accepted the position of the Tzlach.
*Practically, how much is a [[Kezayit]]?  
*Practically, how much is a [[Kezayit]]?  
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#On Mitzvot Deoritta such as eating [[Matzah]] one must be strict to hold a [[Kezayit]] is a half a [[KeBaytzah]]. However, regarding מצות Derabbanan it’s preferable to hold that a [[Kezayit]] is a half a kebaytzah, however, one may rely on the opinion that a [[Kezayit]] is a third a kebaytzah. <ref>Mishna Brurah 486:1 </ref>
#On Mitzvot Deoritta such as eating [[Matzah]] one must be strict to hold a [[Kezayit]] is a half a [[KeBaytzah]]. However, regarding מצות Derabbanan it’s preferable to hold that a [[Kezayit]] is a half a kebaytzah, however, one may rely on the opinion that a [[Kezayit]] is a third a kebaytzah. <ref>Mishna Brurah 486:1 </ref>
#One needs to make sure that he does not count air in the food as part of the shiur of kezayis. If one has a food that is hollow, a kezayis of that food is considered when the food would be pressed.<ref>Rama 486:1 </ref>
#One needs to make sure that he does not count air in the food as part of the shiur of kezayis. If one has a food that is hollow, a kezayis of that food is considered when the food would be pressed.<ref>Rama 486:1 </ref>
#For more opinions of kezayit see: [https://www.ou.org/torah/files/the-kezayit.pdf OU's article on Kezayit].


===Kedi Achilat Pras===
===Kedi Achilat Pras===
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===KeBaytzah===
===KeBaytzah===


#According to Rav Chaim Noeh, the [[KeBaytzah]] is 55cc, and according to the Chazon Ish, it is 100cc. <ref>Vezot HaBracha pg 6 </ref>
#According to Rav Chaim Noeh, the KeBaytzah is 55cc, and according to the Chazon Ish, it is 100cc. <ref>Vezot HaBracha pg 6 </ref>


===Revi'it===
===Revi'it===


#A [[Reviyit]] is a [[KeBaytzah]] and a half.<ref>Mishna Brurah 486:1 </ref> Therefore, Rav Chaim Noeh holds that the [[Reviyit]] is 86 grams (3 oz),<ref>Shiurei Tzion (p. 69)</ref> the Chazon Ish holds that the [[Reviyit]] is 150 grams (5.3 oz).<ref>Rav Chaim Kanievsky in Shiurin Shel Torah (p. 66) according to the rulings of the Chazon Ish </ref>, and some quote Rav Moshe as saying the [[Reviyit]] is 3.3 oz.<ref>Vezot HaBracha (Birur Halacha 1) quotes Haggadat Kol Dodi which quotes Rav Moshe Feinstein as saying that a [[Reviyit]] is 3.3 oz.</ref>
#A Reviyit is a [[KeBaytzah]] and a half.<ref>Mishna Brurah 486:1 </ref> Therefore, Rav Chaim Noeh holds that the [[Reviyit]] is 86 grams (3 oz),<ref>Shiurei Tzion (p. 69)</ref> the Chazon Ish holds that the [[Reviyit]] is 150 grams (5.3 oz).<ref>Rav Chaim Kanievsky in Shiurin Shel Torah (p. 66) according to the rulings of the Chazon Ish </ref>, and some quote Rav Moshe as saying the Revi'it is 3.3 oz. <ref>Vezot HaBracha (Birur Halacha 1) quotes Haggadat Kol Dodi which quotes Rav Moshe Feinstein as saying that a [[Reviyit]] is 3.3 oz.</ref>
#With regards to drinking [[the four cups of wine]], see the [[Required Amount of Matzah and Wine for the Seder]] page.
#With regards to drinking [[the four cups of wine]], see the [[Required Amount of Matzah and Wine for the Seder]] page.


===Kedei Shtiyat Reviyit===
===Kedei Shtiyat Reviyit===


#See [[Kedei Shtiyat Reviyit]] (the time in which a [[Reviyit]] is considered drunk together)
#See [[Bracha_Achrona#Drink |Kedei Shtiyat Revi'it]] (the time in which a Revi'it is considered drunk together).
===Ayfah, Seah, Kav, Log===
{| class="wikitable sortable"
!Shiur<ref>Rashbam Pesachim 108b s.v. dhaynu explains that an ayfeh is three seah, which is six kav, which is four log, which is six kebeytzot. Shulchan Aruch OC 486:1 rules like Tosfot that a Kebeytzah is two kezaytim. For shiur of kezayit see [[#Kezayit]] above.</ref>
!Ayfah
!Seah
!Kav
!Log
!Kebeytzah
!Kezayit
!cm<sup>3</sup>
!inch<sup>3</sup>
|-
|Ayfah
|1
|3
|18
|72
|432
|864
|23328
|1424
|-
|Seah
|1/3
|1
|6
|24
|144
|288
|7776
|475
|-
|Kav
|1/18
|1/6
|1
|4
|24
|48
|1296
|79
|-
|Log
|1/72
|1/24
|1/4
|1
|6
|12
|324
|20
|-
|Kebeytzah
|1/432
|1/144
|1/24
|1/6
|1
|2
|54
|3.3
|-
|Kezayit
|1/864
|1/288
|1/48
|1/12
|1/2
|1
|27
|1.6
|}
#For example the average apple's volume is 104.5 cm<sup>3</sup> which is 3.9 kezaytim.<ref>https://cigrjournal.org/index.php/ejounral/article/view/1124</ref>


==Length==
==Length==
===Amah, Tefach, Etzbah===
===Amah, Tefach, Etzbah===
 
{| class="wikitable sortable"
#According to Rav Moshe Feinstein, the [[Amah]] is 21.25 inches (53.98 centimeters), the [[Tefach]] is 3.54 inches (9.00 centimeters), and the Etzbah is 0.89 inches (2.25 centimeters). <ref>Sh”t Igrot Moshe O”C 1:136. writes that the [[Amah]] is 21.25 inches and one can be strict to hold that it is 23 inches. Similarly, the Aruch Hashulchan YD 286:21 writes that 4 amot is one Russian ''sazhen'' which is the equivalent of 7 feet (see [https://en.wikipedia.org/wiki/Obsolete_Russian_units_of_measurement Wikipedia's page on Russian measurements]) meaning that the amah is 21 inches. [https://asif.co.il/download/kitvey-et/kol/kol-30/1-29.pdf Dr. Gideon Freedman in Kol Bramah v. 4 p. 229] proves that the Aruch Hashulchan YD 201:3 and Mishna Brurah 358:7 both hold that the amah is 21 inches. The Aruch Hashulchan says that an amah is three quarters of a arshin and an arshin is 71.12 cm. The Mishna Brurah ties 53 russian arshins to 70.83 amot. See there for the calculations.</ref>
!
#According to Rav Chaim Noeh, the [[Amah]] is 18.90 inches (48 centimeters), the [[Tefach]] is 3.15 inches (8 centimeters), and the Etzbah is 0.79 inches (2 centimeters) <ref>Shiurei Torah (by Rav Chaim Noeh, Siman 3 Seif 25 pg 249) </ref>
!Amah
#According to the Chazon Ish, the [[Amah]] is 24 inches (60.96 centimeters), the [[Tefach]] is 4 inches (10.16 centimeters), and the Etzbah is 1 inch (2.54 centimeters). <ref>Shiurin shel Torah (pg 3) by the Steipler quoting the Chazon Ish but admitting that these are approximate measures because of the need to publicize the measures but not an accurate calculation. </ref>
!Tefach
!Etzbah
|-
|Rav Moshe Feinstein<ref>Sh”t Igrot Moshe O”C 1:136. writes that the [[Amah]] is 21.25 inches and one can be strict to hold that it is 23 inches. Similarly, the Aruch Hashulchan YD 286:21 writes that 4 amot is one Russian ''sazhen'' which is the equivalent of 7 feet (see [https://en.wikipedia.org/wiki/Obsolete_Russian_units_of_measurement Wikipedia's page on Russian measurements]) meaning that the amah is 21 inches. [https://asif.co.il/download/kitvey-et/kol/kol-30/1-29.pdf Dr. Gideon Freedman in Kol Bramah v. 4 p. 229] proves that the Aruch Hashulchan YD 201:3 and Mishna Brurah 358:7 both hold that the amah is 21 inches. The Aruch Hashulchan says that an amah is three quarters of a arshin and an arshin is 71.12 cm. The Mishna Brurah ties 53 russian arshins to 70.83 amot. See there for the calculations.</ref>
|21.25 in. (53.98 cm)
|3.54 in. (9.00 cm)
|0.89 in. (2.25 cm)
|-
|Rav Chaim Noeh<ref>Shiurei Torah (by Rav Chaim Noeh, Siman 3 Seif 25 pg 249) </ref>
|18.90 in. (48 cm)
|3.15 in. (8 cm)
|0.79 in. (2 cm)
|-
|Chazon Ish<ref>Shiurin shel Torah (pg 3) by the Steipler quoting the Chazon Ish but admitting that these are approximate measures because of the need to publicize the measures but not an accurate calculation. </ref>
|24 in. (60.96 cm)
|4 in. (10.16 cm)
|1 in. (2.54 cm)
|}


===Mil===
===Mil===
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==Time==
==Time==
Generally one can search for zmanim on [http://www.myzmanim.com| myzmanim.com] and for a time according to degrees below horizon anywhere in the world on [https://www.suncalc.org/| suncalc.org].
===Shaot Zmaniot===
===Shaot Zmaniot===


#[[Shaot Zmaniot]] are halachic hours which are calculated by dividing the daytime hours into 12. There’s a dispute of how to measure the day; some count the day from Olot HaShachar until [[Tzet HaKochavim]] (Magen Avraham) <ref>Many authorities holds that the halachic hours in the day are considered from Olot including: Sh”t Trumat HaDeshen 1, Levush 267, Minchat Cohen (Mevoh Shemesh 2:6) in name of Tosfot Ramban and Rashba, Bach (431), Taz 433, Pri [[Chadash]] 443, Magen Avraham 58:1, 433:3, Eliyah Raba 58:2, Mizbe’ach Adama 4a, Mikraeh Kodesh 158b, Mateh Yehuda 433, Sh”t Chaim Shal 2:38(70), Tov Ayin 18:38, Sh”t Teshuva MaAhava 1:25, Shalmei Tzibbur 93c, Chesed Alafim 58:5, Chaye Adam 21:3,27:1, Kitzur Shulchan Aruch 17:1, Magen Giborim (Shiltei Hagiborim 58:3), and Rav Poalim O”C 2:2. </ref>, and some count it from [[HaNetz]] until [[Shekiah]] (Gra).<ref>Many authorities hold that the halachic hours of the day are considered to begin from [[HaNetz]] incluing: Rambam’s Sh”t Pear Hadar 44 (as understood by Halacha Brurah (Shaar Tzion 58:17), Rav Chaim Drok (Noam 9 pg 235), and Orot Chaim 320 against the Yetsiat Mitzmayim (Sefaka Deyoa pg 115)), Siddur Rav Sadyah Goan pg 12, Minchat Cohen Mevoh Hashemesh 2:6 in name of Goanim, Rambam, Rabbenu Yonah, Hagahot Maimon, and Mordechai (Pri [[Chadash]] rejects his proofs), Shiltei Hagiborim on the Mordechai ([[Brachot]] 4:3) (as understood by Magen Avraham 233:3, Shaar Tzion 233:10, and Kaf HaChaim 233:7), Levush (233:1,267), Shaarei Knesset Hagedolah 58:8, Tosfot [[Yom Tov]] (Pesachim 2:3), and Biur HaGra 459:2.</ref>
#[[Shaot Zmaniot]] are halachic hours which are calculated by dividing the daytime hours into 12. There’s a dispute of how to measure the day; some count the day from Olot HaShachar until [[Tzet HaKochavim]] (Magen Avraham) <ref>Many authorities holds that the halachic hours in the day are considered from Olot including: Sh”t Trumat HaDeshen 1, Levush 267, Minchat Cohen (Mevoh Shemesh 2:6) in name of Tosfot Ramban and Rashba, Bach (431), Taz 433, Pri [[Chadash]] 443, Magen Avraham 58:1, 433:3, Eliyah Raba 58:2, Mizbe’ach Adama 4a, Mikraeh Kodesh 158b, Mateh Yehuda 433, Sh”t Chaim Shal 2:38(70), Tov Ayin 18:38, Sh”t Teshuva MaAhava 1:25, Shalmei Tzibbur 93c, Chesed Alafim 58:5, Chaye Adam 21:3,27:1, Kitzur Shulchan Aruch 17:1, Magen Giborim (Shiltei Hagiborim 58:3), and Rav Poalim O”C 2:2. </ref>, and some count it from [[HaNetz]] until [[Shekiah]] (Gra).<ref>Many authorities hold that the halachic hours of the day are considered to begin from [[HaNetz]] incluing: Rambam’s Sh”t Pear Hadar 44 (as understood by Halacha Brurah (Shaar Tzion 58:17), Rav Chaim Drok (Noam 9 pg 235), and Orot Chaim 320 against the Yetsiat Mitzmayim (Sefaka Deyoa pg 115)), Siddur Rav Sadyah Goan pg 12, Minchat Cohen Mevoh Hashemesh 2:6 in name of Goanim, Rambam, Rabbenu Yonah, Hagahot Maimon, and Mordechai (Pri [[Chadash]] rejects his proofs), Shiltei Hagiborim on the Mordechai ([[Brachot]] 4:3) (as understood by Magen Avraham 233:3, Shaar Tzion 233:10, and Kaf HaChaim 233:7), Levush (233:1,267), Shaarei Knesset Hagedolah 58:8, Tosfot [[Yom Tov]] (Pesachim 2:3), and Biur HaGra 459:2.</ref>
##According to Sephardim, regarding Deoritta laws (including [[Kriyat Shema]]) one should be strict for the opinion of the Magen Avraham. <ref>In conclusion, Minchat Cohen (Mevoh Hashemesh 2:9), Erech HaShulchan 433, Halichot Olam (vol 1, Vaera 3), and Yalkut Yosef (vol 1, pg 98) write that one should be strict for the opinion of the Magen Avraham for Deoritta issues, for example [[Kriyat Shema]]. </ref>
##According to Sephardim, regarding Deoritta laws (including [[Kriyat Shema]]) one should be strict for the opinion of the Magen Avraham. <ref>In conclusion, Minchat Cohen (Mevoh Hashemesh 2:9), Erech HaShulchan 433, Halichot Olam (vol 1, Vaera 3), and Yalkut Yosef (vol 1, pg 98) write that one should be strict for the opinion of the Magen Avraham for Deoritta issues, for example [[Kriyat Shema]]. </ref>
##Among Ashkenazim, some are strict to hold like the Magen Avraham, unless there is an serious need, in which case one may hold like the Gra. <ref>Rabbi Yechiel Michel Tukachinsky in Sefer Eretz Yisrael (pg 18#3) writes that the minhag of [[Israel]] is to follow the magen avraham and only under pressure may one rely on the Gra.</ref>However, some are lenient to rely on the Gra. <ref>[http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 77-79) says that many follow the opinion of the Gra in calculating the time for Sof [[Kriyat Shema]]. </ref>
##Among Ashkenazim, some are strict to hold like the Magen Avraham, unless there is an serious need, in which case one may hold like the Gra. <ref>Rabbi Yechiel Michel Tukachinsky in Sefer Eretz Yisrael (pg 18#3) writes that the minhag of [[Israel]] is to follow the magen avraham and only under pressure may one rely on the Gra.</ref> However, some are lenient to rely on the Gra. <ref>[http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 77-79) says that many follow the opinion of the Gra in calculating the time for Sof [[Kriyat Shema]]. </ref>
 
===Olot HaShachar===


#Many rishonim hold that [[Olot HaShachar]] is 72 minutes before sunrise on a "perfect day" (when sunrise and sunset are exactly 12 hours apart) in Jerusalem which is equivalent to when the sun is 16 degrees below the horizon for everywhere in the world, however, others hold that [[Olot HaShachar]] is 90 minutes on a perfect day which is 19.78 degrees below the horizon. <ref>*The Rosh (Brachot 4:1) writes that Olot for the korban tamid and Shacharit is after the rays of the sun begin to show and also the Eastern part of the sky began to become light. This is also the opinion of the Rabbenu Yerucham cited by Bet Yosef 89:1. Shulchan Aruch 89:1 codifies their opinion. Magen Avraham 89:3 argues that many rishonim hold that Olot is once the rays of the sun begin to show even though the Eastern part of the sky isn't light. Torat Yoma 28a siman 11 writes that the Rambam Pirush Mishnayot Yoma 3:1 and Ritva Yoma 28a hold like the Rosh and Rabbenu Yerucham, while Rashi sides with the Magen Avraham. Practically, the Mishna Brurah (Biur Halacha 89:1 s.v. v'im) writes that one shouldn't be lenient for the Magen Avraham as the Eliya Rabba, Mateh Yehuda, and Gra argue with the Magen Avraham. Therefore, Olot is once the rays of the sun began to show and also the Eastern part of the sky became light.
===Alot HaShachar===
*Sefer Zmanim KeHilchatam (Rabbi Berstein, pg 347) writes that 72 minutes on a perfect day in Jerusalem is equal to when the sun is 16 degrees below the horizon and 90 minutes is equal to 19.78 degrees below the horizon. He personally rules that one should be strict for both of these opinions for Deoritta halachas and those derabbanan halachas where safek is lechumra. He tries to prove that this is the opinion of the Mishna Brurah (92:3, Beiur Halacha 163:1 s.v. Berachok). However, he totally rejects the opinion that [[Olot HaShachar]] is 120 minutes before sunrise. [It is noteworthy that astronomical dawn is the time when the Sun is at 18 degrees below the horizon and before then the sky is absolutely dark ([timeanddate.com https://www.timeanddate.com/astronomy/different-types-twilight.html]).]
'''Halacha'''
#Many rishonim hold that [[Alot HaShachar]] is 72 minutes before sunrise on a "perfect day" (when sunrise and sunset are exactly 12 hours apart) in Jerusalem which is equivalent to when the sun is 16 degrees below the horizon for everywhere in the world, however, others hold that [[Alot HaShachar]] is 90 minutes on a perfect day which is 19.78 degrees below the horizon. <ref>*The Rosh (Brachot 4:1) writes that Alot for the korban tamid and Shacharit is after the rays of the sun begin to show and also the Eastern part of the sky began to become light. This is also the opinion of the Rabbenu Yerucham cited by Bet Yosef 89:1. Shulchan Aruch 89:1 codifies their opinion. Magen Avraham 89:3 argues that many rishonim hold that Alot is once the rays of the sun begin to show even though the Eastern part of the sky isn't light. Torat Yoma 28a siman 11 writes that the Rambam Pirush Mishnayot Yoma 3:1 and Ritva Yoma 28a hold like the Rosh and Rabbenu Yerucham, while Rashi sides with the Magen Avraham. Practically, the Mishna Brurah (Biur Halacha 89:1 s.v. v'im) writes that one shouldn't be lenient for the Magen Avraham as the Eliya Rabba, Mateh Yehuda, and Gra argue with the Magen Avraham. Therefore, Alot is once the rays of the sun began to show and also the Eastern part of the sky became light.
*Sefer Zmanim KeHilchatam (Rabbi Berstein, pg 347) writes that 72 minutes on a perfect day in Jerusalem is equal to when the sun is 16 degrees below the horizon and 90 minutes is equal to 19.78 degrees below the horizon. He personally rules that one should be strict for both of these opinions for Deoritta halachas and those derabbanan halachas where safek is lechumra. He tries to prove that this is the opinion of the Mishna Brurah (92:3, Beiur Halacha 163:1 s.v. Berachok). However, he totally rejects the opinion that [[Alot HaShachar]] is 120 minutes before sunrise. [It is noteworthy that astronomical dawn is the time when the Sun is at 18 degrees below the horizon and before then the sky is absolutely dark ([timeanddate.com https://www.timeanddate.com/astronomy/different-types-twilight.html]).]
*He also quotes Rabbi Tukachinsky who held like the opinion of 90 minutes.
*He also quotes Rabbi Tukachinsky who held like the opinion of 90 minutes.
*[http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 65-7) says that we assume that [[Olot HaShachar]] depends on degrees below horizon and the specific times vary according to one’s location. Similarly, [http://www.ou.org/webcast_kosher Rav Yisrael Belsky] (OU Kosher Webcast, 2011, min 19-21) mentioned in passing that [[Olot HaShachar]] is assumed to be 72 minutes before sunrise, varying according to the longitude and latitude.</ref>
*[http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 65-7) says that we assume that [[Alot HaShachar]] depends on degrees below horizon and the specific times vary according to one’s location. Similarly, [http://www.ou.org/webcast_kosher Rav Yisrael Belsky] (OU Kosher Webcast, 2011, min 19-21) mentioned in passing that [[Alot HaShachar]] is assumed to be 72 minutes before sunrise, varying according to the longitude and latitude.</ref>
# According to Sepharadim, Alot HaShachar is 72 minutes before sunrise.<ref> Yalkut Yosef, Kitzur Shulchan Aruch, Siman 58, Seif 3. </ref> These minutes are proportional to the length of the day,<ref> Yalkut Yosef, Pesuke DeZimra and Keriat Shema, pages 432-433 based on Rambam, Perush Mishnayot, Masechet Berachot, Perek 1.</ref> and do not depend on current location.<ref>Zmanim KHalacha, page 43, quoting Hacham Ovadia zt"l. Hence, 72 minutes would be 1.2 multiplied by the day's shaa zmanit. Rabbi Yehuda Levi, author of Zmanim KHalacha, argues with Hacham Ovadia on the same page. He writes that the 72 minutes are not calculated based on the shaot zmaniot and do depend on current location. Rabbi Levi's difficulties stem from the Rambam's language and astronomic calculation. In the Berachot (1:1), Rambam uses a unique Arabic term when referring to alot hashachar, one that is not used in reference to zman Kriyat Shema (Berachot 1:5) or a the time of a mil (Pesachim 3:2). Furthermore, in the winter, it starts to become light earlier than it starts to become light the spring and the fall, despite having shorter shaot zmaniot in the winter; given this reality, it is difficult to justify calculating alot hashachar strictly according to shaot zmaniot. Therefore, Rabbi Levi maintains that alot hashachar's calculation is determined by degrees below the horizon.</ref>
'''Degrees below Horizon'''
# Some hold that Alot is determined degrees below horizon. There are three opinions about the measure of the mil and therefore, there are three opinions of when Alot is:
## 120 minutes by degrees is 25.9 degrees below horizon.<ref>Zmanei Hahalacha Lmaaseh p. 18</ref>
## 90 minutes by degrees is 19.75 degrees below horizon.<ref>Zmanei Hahalacha Lmaaseh p. 18</ref>
## 72 minutes by degrees is 15.99 degrees below horizon.<ref>Zmanei Hahalacha Lmaaseh p. 18</ref>
'''Zmaniot'''
# Some hold that Alot is determined degrees below horizon. There are three opinions about the measure of the mil and therefore, there are three opinions of when Alot is 120, 90, and 72 zmaniot minutes.<ref>Zmanei Hahalacha Lmaaseh p. 18</ref>
'''Fixed Minutes'''
# Some hold that Alot is determined by 4 mil by fixed minutes. There are three opinions as to the measure of the mil and therefore, there are three opinions of when Alot is:
## 120 minutes fixed before Netz.<ref>Zmanei Hahalacha Lmaaseh p. 18 writes that 120 minutes fixed is based on the rishonim that a mil is 24 minutes and there is 5 mil between Alot and Netz.</ref>
## 90 minutes fixed before Netz.<ref>Zmanei Hahalacha Lmaaseh p. 18 writes that 90 minutes fixed is based on the rishonim that a mil is 22.5 minutes and there is 4 mil between Alot and Netz. He writes that Rav Tukachinsky used that for his luach, though he argues that we shouldn't follow it since Shulchan Aruch held of the 18 minute mil.</ref>
## 72 minutes fixed before Netz.<ref>Zmanei Hahalacha Lmaaseh p. 18 writes that 72 minutes fixed is based on the rishonim that a mil is 18 minutes and there is 4 mil between Alot and Netz.</ref>


===MeSheyakir===
===MeSheyakir===
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===Mincha Gedola===
===Mincha Gedola===


#Mincha Gedola is six and a half halachic hours (Shaot Zmaniyot) after sunrise.<ref>Rashi (Pesachim 107a s.v. mincha gedola), Rambam (Tefillah 3:2)</ref>
#Mincha Gedola is six and a half halachic hours (Shaot Zmaniot) after sunrise.<ref>Rashi (Pesachim 107a s.v. mincha gedola), Rambam (Tefillah 3:2)</ref>


===Mincha Ketana===
===Mincha Ketana===


#Mincha Ketana is nine and a half halachic hours (Shaot Zmaniyot) after sunrise.<ref>Rashi (Pesachim 107b s.v. oh), Rambam (Tefillah 3:2)</ref>
#Mincha Ketana is nine and a half halachic hours (Shaot Zmaniot) after sunrise.<ref>Rashi (Pesachim 107b s.v. oh), Rambam (Tefillah 3:2)</ref>


===Shekiyah (Sunset)===
===Shekiyah (Sunset)===
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===Tzet HaKochavim (Emergence of the stars)===
===Tzet HaKochavim (Emergence of the stars)===


#There's a major dispute when Tzet HaKochavim is: Rabbenu Tam assumes that it's about 72 minutes after [[Shekiyah]] and the Gra assumes that it's three quarters of a [[mil]] after [[Shekiyah]], varying according to one's locations. <ref>Rabbi Hershel Schachter on [http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha# yutorah.org (min 43-5)] explains that many practice like the Gra regarding Tzet HaKochavim on [[Motzei Shabbat]]. See Biur HaGra and Mishna Brurah 261. Pri Megadim assumes that according to Rabbenu Tam, 72 minutes is a fixed time, but Mishna Brurah writes that it varies according to one's location.</ref>
#There's a major dispute when Tzet HaKochavim is: Rabbenu Tam assumes that it's about 72 minutes after [[Shekiyah]] and the Gra assumes that it's three quarters of a [[mil]] after [[Shekiyah]], varying according to one's location. <ref>Rabbi Hershel Schachter on [http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha# yutorah.org (min 43-5)] explains that many practice like the Gra regarding Tzet HaKochavim on [[Motzei Shabbat]]. See Biur HaGra and Mishna Brurah 261. Pri Megadim assumes that according to Rabbenu Tam, 72 minutes is a fixed time, but Mishna Brurah writes that it varies according to one's location.</ref>


===Bein HaShemashot===
===Bein HaShemashot===


#[[Bein HaShemashot]] is the time period between certain daytime and certain nighttime. In many halachot, it is considered a doubt whether it is considered day or night and has many practical ramifications. There is a major dispute how long this period is. <ref>*'''(1) Gemara [[Shabbat]]''' 34b says [[Bein HaShemashot]] is considered as a doubt whether it is considered daytime or nighttime. When is [[Bein HaShemashot]]? Rabbi Yehuda says that [[Bein HaShemashot]] starts from [[Shekiyah]] and concludes when the entire ball of the sun has set. Rabbi Yose, however, says that [[Bein HaShemashot]] is as short as the blink of an eye, though R. Yose also agrees that there is a doubt (Tosfot 34b s.v. Rabbi Yose). R. Nechemya says that it is from [[Shekiyah]] and lasts the length of time it takes to walk a half [[mil]]. [Note, a mil is 2000 amot (see above).]
#[[Bein HaShemashot]] is the time period between certain daytime and certain nighttime. In many halachot, it is considered a ''safek,'' or doubt, whether it is considered day or night and has many practical ramifications. There is a major dispute regarding the length of this period. <ref>*'''(1) Gemara [[Shabbat]]''' 34b says [[Bein HaShemashot]] is considered as a doubt whether it is considered daytime or nighttime. When is [[Bein HaShemashot]]? Rabbi Yehuda says that [[Bein HaShemashot]] starts from [[Shekiyah]] and concludes when the entire ball of the sun has set. Rabbi Yose, however, says that [[Bein HaShemashot]] is as short as the blink of an eye, though R. Yose also agrees that there is a doubt (Tosfot 34b s.v. Rabbi Yose). R. Nechemya says that it is from [[Shekiyah]] and lasts the length of time it takes to walk a half [[mil]]. [Note, a mil is 2000 amot (see above).]
*'''Explanation of Rabbi Yehuda's opinion:''' Rabba explains Rabbi Yehuda as saying that [[Bein HaShemashot]] starts from [[Shekiyah]] even though the sky is still red, while Rav Yosef says [[Bein HaShemashot]] starts from when the sun already set. It follows, says the Gemara, that according to Rabba the span of [[Bein HaShemashot]] is 3/4 of a [[mil]] and according to Rav Yosef [[Bein HaShemashot]] is 2/3 of a [[mil]].
*'''Explanation of Rabbi Yehuda's opinion:''' Rabba explains Rabbi Yehuda as saying that [[Bein HaShemashot]] starts from [[Shekiyah]] even though the sky is still red, while Rav Yosef says [[Bein HaShemashot]] starts from when the sun already set. It follows, says the Gemara, that according to Rabba the span of [[Bein HaShemashot]] is 3/4 of a [[mil]] and according to Rav Yosef [[Bein HaShemashot]] is 2/3 of a [[mil]].
*'''Who do we follow, Rabba or Rav Yosef, in explaining Rabbi Yehuda?''' The Rif (15a) writes that since it is unclear whether halacha follows Rav Yosef or Rabba, one should be strict to follow Rabba that [[Bein HaShemashot]] begins at [[Shekiyah]]. Then he says that it seems halacha should follow Rabba because halacha always follows Rabba with three exceptions and this isn't one of them. Similarly, Rambam ([[Shabbat]] 5:4) rules like Rabba that [[Bein HaShemashot]] begins at [[Shekiyah]]. Rabbenu Yonah (quoted by Rosh [[Shabbat]] 2:23) argues that since they're not arguing about which logic is correct but about what Rav Yehuda said the halacha follows both Rabba and Rav Yosef, whichever way will be a stringency. Therefore, in context of [[accepting Shabbat]], Rama 261:1 rules like Rabba that [[Bein HaShemashot]] is 3/4 of a [[mil]].
*'''Who do we follow, Rabba or Rav Yosef, in explaining Rabbi Yehuda?''' The Rif (15a) writes that since it is unclear whether halacha follows Rav Yosef or Rabba, one should be strict to follow Rabba that [[Bein HaShemashot]] begins at [[Shekiyah]]. Then he says that it seems halacha should follow Rabba because halacha always follows Rabba with three exceptions and this isn't one of them. Similarly, Rambam ([[Shabbat]] 5:4) rules like Rabba that [[Bein HaShemashot]] begins at [[Shekiyah]]. Rabbenu Yonah (quoted by Rosh [[Shabbat]] 2:23) argues that since they're not arguing about which logic is correct but about what Rav Yehuda said the halacha follows both Rabba and Rav Yosef, whichever way will be a stringency. Therefore, in context of [[accepting Shabbat]], Rama 261:1 rules like Rabba that [[Bein HaShemashot]] is 3/4 of a [[mil]].
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*'''Does halacha follow Rabbenu Tam?''' The Shulchan Aruch 261:2 rules in accordance with Rabbenu Tam and states that from the beginning of the [[Shekiyah]] until [[Bein HaShemashot]] there's 3.25 [[mil]] and then [[Bein HaShemashot]] itself is .75 of a [[mil]], which is equivalent to the time it takes to walk 1500 [[amot]]. Beiur Halacha 261 s.v. Metechila writes that for sure one should be strict for the Gra not to do any melacha after sunset.
*'''Does halacha follow Rabbenu Tam?''' The Shulchan Aruch 261:2 rules in accordance with Rabbenu Tam and states that from the beginning of the [[Shekiyah]] until [[Bein HaShemashot]] there's 3.25 [[mil]] and then [[Bein HaShemashot]] itself is .75 of a [[mil]], which is equivalent to the time it takes to walk 1500 [[amot]]. Beiur Halacha 261 s.v. Metechila writes that for sure one should be strict for the Gra not to do any melacha after sunset.
*'''(3) Shmuel's opinion:''' Then, Shmuel ([[Shabbat]] 35b) says that [[Bein HaShemashot]] is as long as two stars are seen in the sky, but if there’s only one star, it’s day, and if it’s three, then it’s night. The Gemara then clarifies that the stars which were discussed are medium size stars. Similarly, the Yerushalmi ([[Brachot]], cited by Ran 15a) says that [[Shabbat]] concludes when three stars can be seen in one area and not spread out. The Rambam ([[Shabbat]] 5:4) rules like Shmuel that when three medium size stars are seen it is certain nighttime. The Kesef Mishna ([[Shabbat]] 5:4) is bothered why the Rambam said that [[Bein HaShemashot]] begins from [[Shekiyah]] and ends when three stars are seen, choosing the opinion of Rabba for the beginning of [[Bein HaShemashot]] and Shmuel for the end of [[Bein HaShemashot]]. He answers that really Rabba and Shmuel agree and just describe it differently. This may also be the intent of the Rif (15a) and Rosh 2:23 who say that halacha follows Rabba as a stringency and also quote Shmuel without anyone arguing. See Or Letzion Vol. 1 YD 1:10 who offers a novel interpretation of the opinion of the Rambam that he holds like Rabbi Yose (see there for the halachic implications). See also Beur Halacha 416 who paskens like Rabbi Yose MeIkar HaDin, as well, and Chazon Ovadia Shabbat Vol. 1 pp. 264.</ref>
*'''(3) Shmuel's opinion:''' Then, Shmuel ([[Shabbat]] 35b) says that [[Bein HaShemashot]] is as long as two stars are seen in the sky, but if there’s only one star, it’s day, and if it’s three, then it’s night. The Gemara then clarifies that the stars which were discussed are medium size stars. Similarly, the Yerushalmi ([[Brachot]], cited by Ran 15a) says that [[Shabbat]] concludes when three stars can be seen in one area and not spread out. The Rambam ([[Shabbat]] 5:4) rules like Shmuel that when three medium size stars are seen it is certain nighttime. The Kesef Mishna ([[Shabbat]] 5:4) is bothered why the Rambam said that [[Bein HaShemashot]] begins from [[Shekiyah]] and ends when three stars are seen, choosing the opinion of Rabba for the beginning of [[Bein HaShemashot]] and Shmuel for the end of [[Bein HaShemashot]]. He answers that really Rabba and Shmuel agree and just describe it differently. This may also be the intent of the Rif (15a) and Rosh 2:23 who say that halacha follows Rabba as a stringency and also quote Shmuel without anyone arguing. See Or Letzion Vol. 1 YD 1:10 who offers a novel interpretation of the opinion of the Rambam that he holds like Rabbi Yose (see there for the halachic implications). See also Beur Halacha 416 who paskens like Rabbi Yose MeIkar HaDin, as well, and Chazon Ovadia Shabbat Vol. 1 pp. 264.</ref>
#The Gemara rules that if one does a Melacha on [[Shabbos]] for the duration of Bein Hashemashos on Friday evening and Saturday evening, one has certainly violated [[Shabbos]], and must bring a sin-offering <ref>[[Shabbos]] 35b, Rambam (Hilchot [[Shabbos]] 5:4). This is because if one treats [[Bein Hashemashot]] as day, one broke [[Shabbos]] on Saturday evening. If one treats [[Bein Hashemashot]] as night, one violated [[Shabbos]] on Friday evening. </ref>
#The Gemara rules that if one does a Melacha on [[Shabbos]] for the duration of Bein Hashemashos on Friday evening and Saturday evening, one has certainly violated [[Shabbos]], and must bring a sin-offering. <ref>[[Shabbos]] 35b, Rambam (Hilchot [[Shabbos]] 5:4). This is because if one treats [[Bein Hashemashot]] as day, one broke [[Shabbos]] on Saturday evening. If one treats [[Bein Hashemashot]] as night, one violated [[Shabbos]] on Friday evening. </ref>
#Therefore, one can do no Melacha during [[Bein Hashemashot]] <ref>Mishnah [[Shabbos]] 34b </ref>.
#Therefore, one cannot perform Melacha during [[Bein Hashemashot]]. <ref>Mishnah [[Shabbos]] 34b </ref>


==Miscellaneous==
==Miscellaneous==