Q. The Mishnah Berurah (beginning of siman 229) says that one should not publicize the sighting of a rainbow because it is like Lashon Horah. Should one also refrain from publicizing the event of a lunar eclipse which, according to popular translation of the gemora (Sukka 29a), is referred to as a bad sign for Jews?

A. Although Mishna Berura (229: 1) quotes from Chaye Adam the term “motzei dibo” is does not refer or imply the common lashon hora meaning, but rather conveying something that may be harmful or proscribed to another, as gazing at the rainbow may be. (Taanis 16, Remah, Mishna Berura ibid 5).
However, in regards to announcing or publicizing a lunar eclipse, Horav Shlomo Miller’s Shlit’a opinion is that it is different than a rainbow.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a