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Saying Kiddush Levana under the sky?
One does not say Kiddush Levana under a roof [or other hovering, such as trees, even if he is outside and can see the moon]. However, in a time of need, one may say Kiddush Levana even in his house, if he can see the moon through a window or open door.
If one said Kiddush Levana under a roof, must it be repeated?
No. If one said Kiddush Levana under a roof he nevertheless fulfills his obligation.
When saying Kiddush Levana indoors must one open the window?
In all cases, one must be able to see the moon when he says the blessing. Thus, a window which is not made of clear glass, or is fogged up due to rain, must be opened to allow one to see the moon. If the window is clear and the moon is visible through it, it is disputed amongst Poskim if the window must nevertheless be opened. Some Poskim rule there is no need to open the window if one can see the moon through it. Others rule one must open the window. Practically, one should try to open the window when saying Kiddush Levana indoors in a time of need.
 Rama 426/4; Shiltei Giborim Brachos 9
 See reasons brought below. According to the reason that this is not to be done due to Ohel of Tuma, then it should not be done under any hovering even if one is outside. However according to the reason that one is to greet the Shechina, then so long as one is outside it is valid, even if he is under a hovering. Practically, since we don’t have a clear tradition as to the reason [so writes Shiltei Giborim ibid] therefore one is to be stringent, and so is the custom.
 Rama ibid; Shiltei Giborim ibid
The reason: Some write that the reason behind this custom is not known. [Shiltei Giborim ibid, brought in M”A 426/14] Others write the reason is in order to guarantee that impurity does not hover over anyone. [Maharil, brought in M”A ibid; See Igros Moshe 143] Others write the reason is because it is similar to one who goes outside to greet the king. [Bach 426 and Hagahos Maimanis, M”A 426/14; Taz 426/4] Meaning that since Kiddush Levana is like greeting the Shechina, it is thus not proper to greet it from under a roof and rather one should go outside. [M”B 426/21]
 Such as one is in middle of a festive meal [Rashal] or he is not feeling well, or he is in the midst of gentiles who may harm him [Bach] or there are filthy alleyways outside which are forbidden to have a blessing recited in them. [M”A ibid; See Admur 85/1 regarding filthy areas]
 Bach 426; M”A 426/14; Taz 426/4
 M”B 426/21 “All this is only initially”
 Shvus Yaakov 1/126; Birkeiy Yosef 224/1 brought in Kaf Hachaim 426/19; Shaareiy Teshuvah 426/1; M”B in Shaar Hatziyon 426/4 and 25
 Dvar Shmuel 242 brought in Beir Heiytiv 426/1; P”M 426 A”A 14
 Shaareiy Teshuvah ibid. He concludes that so is implied from the story with the Rashal that he opened the window.