From 9-9:10am on April 3, homes and businesses in Hon Gai, Ha Long City of Quang Ninh Province had to turn on their lights when the sky suddenly darkened. This phenomenon was also observed in other northern provinces. It was brought on by a large storm, with dense clouds covering the sun.

A sun-radiated halo appeared in some localities last year, such as Da Nang, Ba Ria - Vung Tau, Lao Cai, Da Lat and Binh Duong. A halo is an optical phenomenon produced by ice crystals creating colored or white arcs and spots in the sky. Many are seen near the sun or moon but others are elsewhere and even in the opposite part of the sky. In picture: Halo in Bac Kan last August.

Amazing clouds in the sky of Hanoi in August 2009, after heavy rains. Scientists said this phenomenon is not related to any major meteorological events, but the frequency of repetition of clouds [of this type] is very low, so this phenomenon is rare. They are Mammatus clouds.

In July 2012, iridescent clouds appeared in the sky of Hanoi and Vinh Phuc. This phenomenon was previously witnessed in Quy Nhon in June 2012, and is not too rare. Iridescent clouds are generated through diffraction.