THOUGHTS ON THE DAILY DAF
brought to you by Kollel Iyun Hadaf of Har Nof
Rosh Kollel: Rav Mordecai Kornfeld
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Rosh Hashanah 21
ROSH HASHANAH 21 & 22 (12,13 Av) - dedicated by Rabbi Kornfeld's
grandmother, Mrs. G. Turkel, to the memory of her husband, Reb Yisrael
Shimon (Isi) ha'Levi Turkel, who loved Torah and worked to support Torah
until his last breath. He passed away on 10 Av 5780.
1) OPPOSITION OF THE MOON, BY LAND AND BY SEA
QUESTION: Rav Nachman gave advice to people who would be traveling at sea.
Since they had no way of knowing when the new month was declared, they
needed some way of ascertaining the time to get rid of their Chametz. Rav
Nachman told them that when they see the full moon setting at the same time
that the sun rises, that is the day to get rid of their Chametz.
The Gemara asks that we see the moon set at the time the sun rises on the
*fifteenth* of the month, but Chametz must be destroyed on the *fourteenth*!
The Gemara answers that at sea, the horizons are clearer, and therefore the
moon is seen setting at sunrise on the fourteenth of the month, one day
earlier than people on land see it setting at sunrise.
(a) Why is it that on land people see the moon set at sunrise one day later
than those at sea see the same thing?
(b) What day is considered the halfway point through the month? Since the
average month is a little more than 29 1/2 days, half of that is about 14
3/4 days. After 14 3/4 days have passed since the beginning of the month,
the moon should be seen to be setting at the time that the sun rises.
However, Rav Nachman says that the moon can be seen setting at sunrise on
the *fourteenth* day. At sunrise on the fourteenth day of the month, only 13
1/2 days have passed since the new moon! How can Rav Nachman give that as
the time for destroying Chametz?
(a) As we discussed earlier (see Insights to 20b), the moon travels around
the earth slower than the sun. At the Molad, the moon and sun are at the
same point in the sky. As the days pass by, the moon lags farther and
farther behind the sun (that is, it drops another 12 degrees towards the
east each day). Halfway through the month the moon has lagged so far behind
the sun and it is on the other side of the earth, at the opposite horizon
(or 180 degrees away from the sun). The next day it will be only 168 degrees
away, having moved another 12 degrees further from to the east. On that day,
when the sun rises, the moon will be higher up (12 degrees) in the western
sky than it was the day before at sun rise.
At sunrise at the fourteenth day of the month, says Rav Nachman, the moon is
180 degrees away from the sun and at the opposite horizon. It sets at
sunrise. This opposition, however, can only be witnessed properly by sea,
when the horizon is unobstructed. On land, though, there are obstructions in
both the eastern and western horizons. If the obstructions are tall enough
in each horizon (about 6 degrees), one will see the moon setting at the time
the sun rises when they are actually closer together by 12 degrees, or only
168 degrees apart from each other. Thus, people on land will see the moon
setting at the time the sun rises one day later, on the fifteenth of the
(b) The answer to our question about the midpoint of the month is that in
the days of Rav Nachman, they still declared the new month based on the
testimony of witnesses. The new moon was visible for the first time only 6
hours after the Molad when the Molad occurred before midday, or 18 hours
after the Molad when the Molad occurred after midday. Therefore, day 13 1/2
of the Hebrew month (that is, 13 1/2 days from the day that Beis Din
declared to be the new month) is actually between day 14 and 14 1/2 from the
time of the Molad of the new moon. Therefore, Rav Nachman could accurately
say that the people at sea could determing the day of Bi'ur Chametz, the
fourteenth of Nisan, by seeing the moon setting at the time of sunrise.
(KUNTRAS "DI SHEMAYA")