§ Caused by sunlight being blocked by high-rise objects (such as cumulus clouds or high mountains), creating strips of alternating bright and dark rays. The rays appear to converge on the sun.
§ At sunrise or sunset, crepuscular rays would appear to converge at the antisolar point.
§ An optical phenomenon caused by refraction of sunlight by ice crystals
§ The sky is typically covered by cirrostratus or thick cirrus when it occurs
§ The most common halo is a luminous ring of 22 degrees radius surrounding the sun, with the space within the ring appearing less bright than that just outside
§ On average, solar halo is observed in Hong Kong on about 3 days in a year
§ An optical phenomenon caused by diffraction of sun or moon light by very tiny cloud droplets
§ Usually appears in altocumulus and altostratus clouds close to the sun or moon
§ Includes colours such as light green, light blue and light pink
§ The way light is diffracted depends on the size of cloud droplets, therefore the colours and shapes of iridescent clouds change rapidly with time
§ A type of man-made clouds and are mainly formed by jets
§ Water vapour from aircraft exhaust condenses in the surrounding cold air, producing water droplets and ice crystals, leaving a trail aloft
§ An optical phenomenon caused by refraction of sunlight by water droplets
§ Blue light has a shorter wavelength and is refracted more than light with a longer wavelength such as red light, therefore blue light is located in the inner part of the rainbow, while red light is located in the outer part
§ Each of the colours in the rainbow comes to the eye from a different set of water droplets