A weekly feature of Torah Tidbits to help clarify practical and conceptual aspects of the Jewish Calendar, thereby better fulfilling the mitzva of HaChodesh HaZeh Lachem...
The molad of Iyar was Monday night, 10:15pm Israel Summer time. This means that the earliest (and best) opportunity for Kiddush L'vana would be 3 full days later (we're talking Minhag Yerushalayim, a.k.a. the GR"A's shita), which is Thursday night (APR 22) at 10:15pm. Problem is that by 10:15 the moon will have set. Therefore, the following night would be prime for K.L. Except that the following night is Leil Shabbat, when we don't say K.L. unless it's the last op. Motza'ei Shabbat it is! And that's nice, because Motza"Sh is the special time to say K.L.
Interesting note: The actual molad was Monday at 4:21pm. Which means that on Thursday night the moon will actually be 3 full days old. Nonetheless, we do not go by the reality, rather by our calc.