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Until what day of the month may Kiddush Levana be said-Part 2-Bedieved & How to calculate
Initially one is to be very careful to recite Kiddush Levana prior to 14 days 18 hours and 396.5 chalakim past the Molad. However, in the event that one already missed the time of the first/earliest opinion, one is to contact a Rav for direction as whether he may rely on one of the later approaches. In all cases one may read the blessing from the Tur or Gemara.
The three main opinions [for actual accurate calculation-see next step!]
Molad of Adar was on Monday evening, the 30th of Shevat, at 12:00 AM [Jerusalem time]:
- First opinion of [14 days and 18:22 hours]: Kiddush Levana may be said until Monday evening, the 14th of Adar 1, until 6:22 p.m [in Jerusalem]. [In the Diaspora, it can only be said until this time arrives in Jerusalem.]
- Second opinion [15 days]: Kiddush Levana may be said until Tuesday evening, the 15th of Adar 1, until 12:00 a.m [in Jerusalem]. [In the Diaspora, it can be said until this time arrives in Jerusalem.]
- Third opinion [15 days 12 hrs 22 min]: Kiddush Levana may be said until Wednesday 12:22 p.m, the 15th of Adar 1, until 12:00 p.m [in Jerusalem]. [In the Diaspora, it can be said until this time arrives in Jerusalem.]
How to calculate the end time for Kiddush Levana:
- Step 1-Molad time: Look up the exact time that the Molad occurred in Jerusalem [See https://www.torahcalc.com/molad/ to look up what time the Molad of the current month took place in Jerusalem].
- Step 2-Detract solar versus watch time difference: Detract 21 minutes from that time to supplement for the difference between the current watch time in Jerusalem versus the real solar time [Jerusalem is 21 minutes later than its real solar time.]
- Step 3-Calculate to your local time zone: Calculate the exact time it was in your time zone when the Molad occurred in the above calculated time in Jerusalem.
- Step 4-Add end time of Kiddush Levana: Add the end time of Kiddush Levana in accordance to whatever opinion you follow.
Example for one in New York:
- Molad in Jerusalem occurred at 11:57 p.m on a Monday night, the 30th of Shevat
- Minus 21 minutes = 11:36 p.m.
- Seven hours back for New York time zone = 4:36 p.m, Monday afternoon, 29th of Shevat.
- Add opinion of end time for Kiddush Levana, calculating it from 4:36 p.m. Thus, for example, according to the first opinion, add 14 days 18 hrs and 22 min, to the above time achieved in step 3. This would calculate the end time of Kiddush Levana in Jerusalem to be on Tuesday the 14th Adar 5:58 p.m. and in New York on Tuesday the 14th of Adar 9:58 a.m.
One is to beware to recite Kiddush Levana prior to 14 days 18 hours and 396.5 chalakim past the Molad. If it is past the first half of the month, one is to contact a Rav.
Story of Rebbe Rashab from memoirs of Rav Yaakov Landau-Free Translation
Date: Motzei Shabbos Beshalach 18th Shvat,
A number of members of Anash, myself included, had not recited Kiddush Levana, and on Friday night the moon became visible. I entered into the Rebbe Rashab during the Shabbos Friday night meal, after the Chazara on the Mamar “Az Yashir”, in order to ask his opinion whether to say Kiddush Levana or not.
The Rebbe Rashab replied to me: There is a lengthy discussion on this matter. Reb Dovid Openhaimer has a lengthy response on this, and he concludes that one is to say Kiddush Levana [on Shabbos]. However the Shvus Yaakov rules one is not to say Kiddush Levana. Reb Dovid Openhaimer discusses these points and he says that there are no Techumin [above ten Tefachim] and that all the prayers are elevated. The Shvus Yaakov however negates this.
Reb Yaakov Landau then asked: The above discussion [mentioned in the Shvus Yaakov and Rav Dovid Openhaimer] is only with regards to saying Kiddush Levana on Shabbos, however today [on the 17th of Shvat] it is also after the time.
The Rebbe Rashab replied: Tonight is already passed the time of Kiddush Levana. (The Rebbe then began calculating the amount of time that had passed since the Molad and the last time for Kiddush Levana had been on Thursday night.) The Rebbe then concluded “if so then it is better to say it tomorrow than to say it tonight.” It once occurred by my father [The Rebbe Maharash] that they recited Kiddush Levana 17 days after the Molad. However on Shabbos I never saw him say Kiddush Levana. This occurred in Lubavitch. After my father [the Rebbe Maharash] passed away it once occurred that the congregation recited Kiddush Levana on the second night of Sukkos. I said Kiddush Levana earlier. I saw the moon earlier so I already said the Bracha, however the rest of the congregation said it on the second night of Sukkos. (The Rebbe then mentioned to me a certain Rabbi that ruled they should say Kiddush Levana then.) Midmuvsky then reminded me that Reb Yisrael Noach once said Kiddush Levana on the second night of Pesach. Based on this one can also say Kiddush Levana on Shabbos as it is the same reason. Nevertheless I never witnessed anyone saying Kiddush Levana on Shabbos and in truth it is a bit difficult to accept such a practice. In my father’s time there were those that said Kiddush Levana after 17 days passed from the Molad. They awoke before daybreak and said Kiddush Levana. My father was always accustomed to awaken before daybreak however us they had to especially awaken for this occasion. That entire night someone stood guard outside to see if the moon would be seen. Feivish was standing guard. Practically, it is better [for Rav Landau] to say Kiddush Levana tomorrow night than to say it tonight. Tomorrow is the 17th day past the Molad. The Molad was at 12:00, thus you can say it tomorrow. Regarding saying Kiddush Levana on the 16th such an opinion is recorded in the Heishiv Moshe, however this was seemingly the occurrence with my father [the Rebbe Maharash].
The Rebbetzin Shterna Sara stated: I remember that at that night they all went outside with Sefarim.
The Rebbe Rashab replied: This occurred very late at night.
Rav Yaakov Landau asked: So it was said without the loophole of using a Gemara or Rif.
The Rebbe Rashab replied: Without using any loopholes. To do loopholes you don’t need to wait for the date to be the 17th, you can do it anytime.
Story of the Tzemach Tzedek and Reb Hillel Paritcher
During a certain snowy winter month Reb Hillel visited the city of Lubavitch, the town of residence of the Tzemach Tzedek. The moon had yet to be seen during that month and the last possible day to say Kiddush Levana had arrived. Reb Hillel sent a Pan to the Tzemach Tzedek to receive a blessing that the moon should be seen that night. The Tzemach Tzedek guaranteed Reb Hillel that the moon would indeed appear. Reb Hillel proceeded to station people outside as guard to announce to him when the moon becomes visible. In the midst of the night word came to Reb Hillel that the moon has appeared. Upon going outside, he saw that the moon was a bit blurry covered by light clouds. He said that the Tzemach Tzedek said the moon would be seen, and therefore it has to be seen in a clear fashion, so he returned back inside waiting for a clearer appearance. Slightly prior to daybreak the moon appeared clearly without any clouds interfering. Reb Hillel immediately went outside and recited Kiddush Levana. He then remarked that it once happened in his younger age that an entire month passed without a visible moon, although back then he was strong enough to handle such an occurrence. However, now in his old age he does not know how he would have been able to react if the moon had not been seen.
 Kaf Hachaim 426:53 that so applies even for Sephardim that they should suspect for the opinion of Rama ibid
 M”B in Biur Halacha ibid concludes one may be lenient like Michaber ibid; Hiskashrus 961 writes [Vetzaruch Iyun as to his source] that one may say Kiddush Levana up to 18 hours past the time of the Rama [15 days 12 hours and 22 minutes from the Molad] as rules the Chasam Sofer, however he may not say it anymore once 18 hours have passed. In correspondence with Rav Ginzberg he wrote to me that this was the ruling of Rav Yaakov Landau, as was told to him by his son Rav Eliyahu Landau, that after 18 hours of the time of the Rama one may not be lenient to say it. This is despite the fact that the story mentioned above took place with Rav Yaakov Landau and he received a directive from the Rebbe Rashab to say Kiddush Levana on the night of the 20th. This story had been authenticated by the Rebbe Rayatz and was passed over his holy eyes prior to its publishing. Nevertheless, in actuality we are not lenient to rule this way. In an earlier volume of Hiskashrus  as well as in the glosses of Rav Raskin on the Siddur they wrote one may rely on the above story and recite Kiddush Levana even past the above time.
 Poskim stated in previous footnotes, see there. See glosses of Rav Raskin on Siddur who writes he recalls a directive of the Rebbe to say it from the Gemara when it is being said past the time.
Background: There are two important ways of describing time. “Clock time” is the artificial time that we use in everyday life to standardize our time measurements. It allows people in different locations to use the same time or to easily convert time from one location to another. “Local solar time” (or simply “solar time”) is the time according to the position of the sun in the sky relative to one specific location on the ground. In solar time, the sun is always due south (or north) at exactly noon. This means that someone a few miles east or west of you will realize a slightly different solar time than you, although your clock time is probably the same. For the purpose of calculating local solar time, clock time must modified to compensate for three things: (1) the relationship between the local time zone and the local longitude, (2) daylight savings time, and (3) the earth’s slightly-irregular motion around the sun (corrected for using the equation of time). Local solar time (LSoT) is calculated as follows: LSoT = LST + 4 minutes * (LL – LSTM) + ET Where: LST (local standard time) = Clock time, adjusted for daylight savings time if necessary. LL = The local longitude; positive = East, and negative = West. LSTM = The local standard time meridian, measured in degrees, which runs through the center of each time zone. It can be calculated by multiplying the differences in hours from Greenwich Mean Time by 15 degrees per hour. Positive = East, and negative = West. ET = The equation of time adjustment in minutes.
 Brought in Shemuos Vesippurim p. 182; This story was reviewed and authenticated by the Rebbe Rayatz. [See Kfar Chabad 986]
 This story took place in 1919, of which Motzei Shabbos was the 18th of Shevat. The original mistakenly states the 19th of Shevat.
 The story was written by Rav Yaakov Landau.
 Shemuos Vesipurim Vol. 2 p. 57