The Rainbow

The group was learning the Daf Hayomi as usual, and they were up to Kesuvos daf 77b. They had reached the Gemara’s description of the meeting between Rabbi Yehoshua ben Levi and Rabbi Shimon bar Yochai. Rabbi Shimon asked Rebbi Yehoshua ben Levi, “Was the rainbow ever seen in your day?”
“Yes, it was,” answered Rabbi Yehoshua.
Rabbi Shimon bar Yochai declared, “If so, you are not worthy of the proclamation that Eliyahu Hanavi had made earlier on your behalf: ‘Make way for ben Levi!’”
The Maggid Shiur said, “Rashi explains that the rainbow is a heavenly sign of the promise that Hashem made to spare the world from another flood. If there is a complete tzaddik living in the generation, there is no need for such a sign.”
One of the members of the shiur interjected, “I don’t understand this at all. A rainbow is the natural result of the refraction of light through a prism. How can we say that the presence of a tzaddik worthy of protecting the generation from a flood can be seen in the absence of a rainbow? Isn’t it just a natural part of creation?”
The Maggid Shiur replied, “The Rama answered this question in a very beautiful and simple way. In the years before electric lighting, the only way that a rainbow could be seen by a large group of people at once was when it rained during the day—that is the sunlight just after a rainstorm refracting through the remaining moisture in the air. The gemara in Taanis 23a and the Sifrei in Eikev explain the verse, ‘V’nasati matar artzechem b’ito’—‘and I will send the rain of your land in its proper time,’ to mean that when the Jewish people are worthy, Hashem will only send rain on Tuesday night and Leil Shabbos.
The Maggid Shiur concluded, “This is why the rainbow is not seen when there is a true tzaddik in the generation. When we are zocheh through the great merit of a very elevated tzaddik, it rains at night when there is no light!”