A rare phenomenon for Portugal was spotted and photographed from Praia do Cabeço, in Castro Marim.
A Solar Halo occurs when fine ice particles are suspended in the atmosphere, which reflect sunlight at a certain angle to the earth.
The event is uncommon in Portuguese but found often in other parts of the world. These Halos range from coloured or white rings to arcs and spots in the sky.
Many appear near the sun or moon with the most common being the circular halo, properly called the 22° Halo, when ice crystals typically are suspended in cirrus or cirrostratus clouds in the upper troposphere (5 to 10 kilometres above the earth’s surface.)
The particular shape and orientation of the crystals are responsible for the type of halo observed. Light is reflected and refracted by the ice crystals and may split into colours because of dispersion. The crystals behave like prisms and mirrors, refracting and reflecting light between their faces, sending shafts of light in particular directions.
The Solar Halo spotted from Castro Marim appeared as a large ring around the sun with a radius of about 22°. As a result of the optical properties of the ice crystals involved, no light is reflected towards the inside of the ring, leaving the sky noticeably darker than the sky around it, and giving it the impression of a hole in the sky.
The 22° halo is not to be confused with the corona, which is a different optical phenomenon caused by water droplets rather than ice crystals, and which has the appearance of a multicoloured disk rather than a ring.
The phenomenon from Castro Marim lasted about half an hour and was first witnessed at 14:00 on Friday, June 1st.
