==Food or Drink==
# 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. * 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># 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]]? **(1) 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.
**(2) 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. see also Chazon Ish in Hilchot [[Shabbat]] 39.
**(3) Vezot HaBracha (Birur Halacha 1) quotes Haggadat Kol Dodi which quotes Rav Moshe Feinstein as saying that a [[Kezayit]] is 31.2cc. [However, Rabbi Bodner in Halachos of K’zayis (p. 24) writes that Rav Dovid Feinstein told him that Rav Moshe never measured the eggs himself and it was his student who calculated 1.1oz, but that if his calculations were more precise he should use those. Therefore, Rabbi Bodner rules, based on his own calculations, that a [[Kezayit]] is 27.2cc.]
**(4) 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.</ref>## The minhag of the world and many other authorities is to follow Rav Chaim Noeh’s opinion. <
Ref> Vezot HaBracha (pg 6, Birur 1, pg 221) quotes Rav Elyashiv and Rav Shlomo Zalman saying that for [[Bracha Achrona]] the widely accepted measurement of the [[Kezayit]] is according to Rav Chaim Noeh. Vezot HaBracha also mentions that such is the minhag of the world. </ref># If one ate between a third and a half a [[KeBaytzah]] one should not make a Bracha achrona because of safek [[Brachot]]. Therefore, one should have less than a third and not make a Bracha achrona or more than a half and make a Bracha achrona. < 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>
===Kedei Achilat Pras===
# See [[Kedi Achilat Pras]] (the time in which a [[Kezayit]] is considered eaten together)
# According to Rav Chaim Noeh, the [[KeBaytzah]] is 55cc, and according to the Chazon Ish, it is 100cc. <ref>Vezot HaBracha pg 6 </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 [[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># With regards to drinking [[the four cups of wine]], see the [[Required Amount of Matzah and Wine for the Seder]] page.
===Kedei Shtiyat Reviyit===
# See [[Kedei Shtiyat Reviyit]] (the time in which a [[Reviyit]] is considered drunk together)
===Amah, Tefach, Etzbah===
# 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># 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>
# When [[Mil]] is given in terms of time, some consider it 18 minutes, some 22.5 minutes, and some 24 minutes. <ref>Shulchan Aruch 459:2 writes that the [[mil]] is 18 minutes. Rama 261:1 agrees. Beiur Halacha 459:2 s.v. Haviy quotes some who consider it 22.5 minutes and others who say that it is 24 minutes.</ref># When [[Mil]] is given in terms of distance it is equal to 2000 [[Amot]]. <ref>Rashi Yoma 67a s.v. shivah and Tosfot Shabbat 34b s.v. safek write that a mil is 2000 amot. Shulchan Aruch 261:2 writes that 3/4 of a [[mil]] is equal to 1500 [[amot]], implying a [[mil]] is 2000 [[amot]]. [http://www.yeshiva.org.il/midrash/shiur.asp?id=15883#3b Rabbi Melamed on yeshiva.org.il] writes that a [[mil]] is 2000 [[amot]].</ref>
# A [[prutah]] is 1/40 of a gram of silver (which is about a few cents). However, the [[prutah]] with regards to the mitzvah of returning a lost object is discussed [[Returning_Lost_Objects#Worth_a_Prutah| here]]. <ref> S”A CM 88:1 says a [[prutah]] is a half of a pearl of barley. Shiurei Torah (Rav Chaim Noeh pg 177) and Shiurei HaMitzvot (Chazon Ish pg 65) say a [[prutah]] is 1/40 of a gram of silver (which currently is about 2.3 cents). Halachos of [[Chanukah]] (Rabbi Shimon Eider, pg 38) quotes Rav Moshe Feinstein saying that a [[prutah]] is 2 or 3 cents and not just one penny. See Halachos of Other People’s Money (Rabbi Bodner pg 150) who quotes Rav Moshe regarding a [[prutah]] for the mitzvah of returning a lost object. </ref>
# If someone steals someone else's mitzvah they should pay them the 10 zehuvim, which is equal to 1200 grams of silver (roughly $650 but varies).<ref>Rav Chaim Noeh (Shiurei Torah p. 379 ch. 3 n. 45) writes that the 10 zehuvim are equal to 250 silver dinar which are 1200 grams of silver.</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>## 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>
# 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.* 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]).]* 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>
# There is a wide range of opinions precisely when Misheyakir occurs in Jerusalem on a perfect day, when there is exactly 12 daylight hours and every seasonal hour consists of 60 minutes. The three opinions include: 35 minutes before sunrise,<ref>Rav Moshe Feinstein in Le-Torah ve-Hora'ah Vol. 3:7 and in Iggeros Moshe OC 4:6 holds of 35 minutes. Rav Yaakov Kamenetsky in Emes liyaakov OC 58:1 rules that it is 36 minutes before sunrise. Zmanei Halacha LeMaaseh (pg 19) holds of 40 minutes before sunrise. </ref> 60 minutes before sunrise,<ref>Rav Tukaczinsky in Sefer Eretz Yisrael 1:4 (pg 18), Kaf HaChaim 18:18, Sh"t Binyan Tzion 2:16 hold of 60 minutes before sunrise. Nivreshet (vol 1, pg 43) holds of 52 minutes.</ref> and 66 minutes before sunrise.<ref>Rav Ovadya Yoseh in Yechave Daat 2:8</ref> # The various opinions would then have to be extrapolated according to the region of the world and time of year.<ref>* There are two factors at work here: First, the processes of daybreak and nightfall occur faster at places near the equator than places further away from the equator. Second, the speed of these processes are also affected by the seasons.
* A common solution would be to use seasonal minutes. In order to calculate a seasonal hour, one would need to add up all the daytime minutes and then divide by 12 to get the number of minutes that are in each seasonal hour. For instance, if there were 11 hours of daylight, each seasonal hour would consist of 55 minutes. To further complicate matters, there are two ways of counting the daytime minutes: The Magen Avraham counts from dawn until nightfall with the emergence of 3 stars, whereas the Gra counts from sunrise to sunset. * Another means for calculation, which has only recently been implemented, is to compare the level of brightness by using the relative position of the sun. For instance, it has been determined that 60 minutes before sunrise on a perfect day in Jerusalem the sun is 12.9 degrees below the horizon. Therefore, if one wanted to find the equivalent time anywhere in the world during any season, he would simply determine at what time the sun will be 12.9 degrees below the horizon in that locale on that day and that would be the extrapolated Meshiyakir.</ref> Thus, according to the commonly accepted opinion that Meshiyakir is between 50 and 60 minutes before sunrise in Jerusalem - In New York, depending on the time of the year, it could be anywhere from 56-73 minutes before sunrise.<ref>MyZmanim.com. These figures are determined using MyZmanim’s earliest published position of 11.5 degrees below the horizon. Unfortunately, MyZmanim.com only offers calculations based upon 10.2 degrees, 11 degrees, and 11.5 degrees but not 12.9 degrees. It is unfortunate because 12.9 degrees correlates to Rav Tukaczinsky’s 60 minutes before sunrise which, although is a very lenient position is also well collaborated and accepted. * [http://www.ou.org/webcast_kosher Rav Yisrael Belsky] (OU Kosher Webcast, 2011, min 21-23) mentions in passing that [[MeSheYakir]] is about 40 or 50 minutes before sunrise.* [http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 68-70) says that Rav Moshe held [[MeSheYakir]] is between 35-40 minutes before sunrise and seems to agree with him, although he mentions that some say it’s 55 minutes before sunrise.</ref>
===HaNetz HaChama (Sunrise)===
# [[HaNetz HaChama]] is sunrise which is halachically the same as the astronomical calculation of sunrise.<ref>* [http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 69-72) says that sunrise is the same as the sunrise calculated by the naval observatory which is when the sun begins to rise. Halacha Brurah 58:7 proves that netz is astronomical sunrise when the upper edge of the sun is on the horizon as opposed to the opinion of the Divrei Dovid 36 and Ben Ish Chai Vayishlach no. 4 that it is 2.6 minutes earlier. * [http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 72-77) says that sunset should be determined as though the mountains to the east and west are at sea level and do not block the visibility of the sun. However, the elevation of the place one is currently located is taken into consideration and if one is in a valley the sunset is a little later (less than 5 minutes) than what would have been visible. Yet, he adds, that most opinions hold that regarding sunrise both one’s location’s elevation and surrounding mountains are taken into consideration. </ref> This is the standard time printed for netz such as on myzmanim.com.
# [[Chatzot]] is midday and midnight, always separated by 12 hours.<ref>Mishna Brurah 1:9 writes that [[chatzot]] at night is always 12 hours after [[chatzot]] of day for any place in the world.</ref>
# 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 Ketana is nine and a half halachic hours (Shaot Zmaniyot) after sunrise.<ref>Rashi (Pesachim 107b s.v. oh), Rambam (Tefillah 3:2)</ref>
# [[Shekiyah]] is sunset which, in general, is halachically the same as the astronomical calculation of sunset. <ref>[http://www.yutorah.org/lectures/lecture.cfm/728553/Rabbi_Hershel_Schachter/Shiur_on_Zmanim_in_Halacha Rav Hershel Schachter on yutorah.org] (min 69-72) says that sunset is the same as the sunset calculated by the naval observatory which is when the sun has completely set. </ref>
===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>
# [[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).]* '''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]].* '''Explanation of Rabbi Yose's opinion:''' Shmuel ([[Shabbat]] 35a) says that Rav Yose’s concept of [[Bein HaShemashot]] takes place after the [[Bein HaShemashot]] already finished. Tosfot ([[Shabbat]] 34b s.v. Rabbi Yose) explains that even according to Rabbi Yose there’s a window of time when there is an uncertainty whether it is day or night but it isn’t as long as it is for Rabbi Yehuda. Rosh (Shabbat 2:23) discusses whether Rabbi Yose's [[Bein HaShemashot]] begins immediately after Rabbi Yehuda's or a while afterwards and doesn't come to a clear conclusion. Rashi to 35a s.v. Bein HaShemashot DeRabbi Yose seems to hold that it is right after R. Yehuda's period.* '''Who does the halacha follow? Rabbi Yehuda or Rabbi Yose''' The Briatta ([[Shabbat]] 34b) says that in regards to practical ramifications [[Bein HaShemashot]] is always considered day as a stringency and night as a stringency. Rif ([[Shabbat]] 14b) and Rambam ([[Shabbat]] 5:4) codify this Briatta. Shulchan Aruch 261:1 rules that during [[Bein HaShemashot]] one may not do anything one may not do on [[Shabbat]] with some exceptions (see there). Therefore, Rabbi Yochanan ([[Shabbat]] 35a) says that we follow Rabbi Yehuda regarding [[Shabbat]] as a stringency and Rabbi Yose regarding Trumah as a stringency. Rif (15a) and Rosh 2:23 codify Rabbi Yochanan as halacha.* '''(2) Gemara Pesachim''' 94a records Rabbi Yochanan's statement that an average person can walk 30 [[mil]] from [[HaNetz HaChama]] until [[Shekiyah]] and 5 [[mil]] from [[Shekiyah]] until [[Tzet HaKochavim]] (according to Rashi s.v. Ovav). The Gemara challenges this and explains really an average person can walk 32 [[mil]] from [[HaNetz HaChama]] until [[Shekiyah]] and only 4 [[mil]] from [[Shekiyah]] until [[Tzet HaKochavim]]. * '''The opinion of Rabbenu Tam:''' Tosfot (Pesachim 94a s.v. Rabbi Yehuda and [[Shabbat]] 35a s.v. Trei) is bothered how the Gemara [[Shabbat]] seems to say that from [[Shekiyah]] until [[Tzet HaKochavim]] a person can walk 3/4 of a [[mil]] (according to the Rabba) and the Gemara Pesachim says a person can walk 4 [[mil]]. Rabbenu Tam answers that the Gemara [[Shabbat]] was referring to the end of the [[Shekiyah]] and from then until [[Tzet HaKochavim]] is 3/4 of a [[mil]], while the Gemara Pesachim is discussing the beginning of [[Shekiyah]] which takes 4 [[mil]] until [[Tzet HaKochavim]]. Ramban (cited by [[Maggid]] Mishna), [[Maggid]] Mishna ([[Shabbat]] 5:4), and Ran ([[Shabbat]] 15a) agree. The Ran ([[Shabbat]] 15a) explains that according to Rabbenu Tam there's two Shekiyot. After the first it is still considered daytime until 3.25 [[mil]] after the beginning of the [[Shekiyah]]. [[Bein HaShemashot]], which is uncertain day or night, spans 3/4 of a [[mil]] and begins from the beginning of the second [[Shekiyah]]. See Beiur Halacha 261 s.v. Metechila who explains that the first [[Shekiyah]] is when the sun sets from our vision, and the second [[Shekiyah]] is when the light from the sun leaves the sky.* '''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># 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>.
===Toch Kedei Dibbur===
# [[Kedei Dibbur]] is the time it takes to say Shalom Alecha Rebbe. <ref>Kitzur Shulchan Aruch (Klalim s.v. Kedei)</ref># [[Toch Kedei Dibbur]] is less than the time it takes to say Shalom Alecha Rebbe.<ref>Kitzur Shulchan Aruch (Klalim s.v. Kedei)</ref>
# There are several opinions about how long Kdei Aniva is, however, one doesn't need to be strict to consider it to be longer than 2 gudalin. <ref>How long is kdei aniva? There’s several opinions about this topic: * Smag- long enough to loop around all the rest of the 7 strings. * Chayei Adam, Kitzur Shulchan Aruch 9:13- 4 gudalin, Beiur Halacha: 2 gudalin, Eliya Rabba (paskening like Rif and Rosh)- long enough to loop around just 1 string (very short). * The Beiur Halacha concludes that there’s no need to be strict for more than 2 gudalin. And he says if you have no choice, you can rely on the Eliya Rabba. see [http://ph.yhb.org.il/07-08-11/ Peninei Halacha] </ref># How long is the shiur of 2 godlin in practical terms? Chazon Ish : 5 cm, Rav Chaim Naeh: 4 cm. Rav Mordechai Eliyahu (comments to Kitzur 9:13) writes that Kedi Anivah is 4 cm.
===Yad Soledet Bo===
# For purposes of cooking on Shabbat and Kashrut, Yad Soledet Bo is certainly hotter than 113 degrees Fahrenheit. <ref>Shemirat Shabbat Kehilchata (ch. 1, note 3), Badei Hashulchan 92:151</ref> Others are concerned for anything over 110 degrees Fahrenheit and over 160 degrees is certainly yad soledet bo. <
Ref>Igrot Moshe (OC 4:74 Bishul no. 3), The Laws of Kashrut p. 111). [https://www.yutorah.org/sidebar/lecture.cfm/788227/rabbi-hershel-schachter/kashrus-in-the-home/ Rav Hershel Schachter ("Kashrus in the Home" 2012, about min 30)] quotes Rav Soloveitchik that yad soledet bo is at least 140 degrees and no more than 160 degrees.</ref>
* [http://www.yutorah.org/lectures/lecture.cfm/763395/Rabbi_Michael_Taubes/_Parshas_Eikev_How_Big_is_a_Kezayis_ How Big is a Kezayis] by Rabbi Michael Taubes