Halo hailed for dazzling appearance around sun

Natural phenomenon grips imagination of public and prompts social media reaction

Hong Kong was dazzled yesterday by a halo around the sun, a natural phenomenon that can only be seen when meteorological conditions are right.

The Hong Kong Observatory posted pictures on its social media accounts at noon that showed a halo above its headquarters and asked the public to share images of the circular light as seen in their areas.

Dozens of people took to social media to share their views of the halo and discuss the meteorological marvel, which has been visible several times this month.

Jennifer Yip Ling, a scientific officer at the Observatory, said halos could be formed all year round and had been spotted several times in the past few years.

The circular or curved white ray of light can be seen to encircle the sun and create a halo effect when weather conditions are favourable.

It is produced when sunlight is reflected or refracted by ice crystals suspended high in the atmosphere.

“High clouds would be required … there would be some ice crystals in the high clouds and sunlight would need to be shining through the layers,” Yip said.

High clouds are typically formed 7,000 to 12,000 metres above the ground.

They are often translucent and are created where ice crystals aggregate in the atmosphere.

A halo is also sometimes accompanied by “sundogs”, bright spots in the sky that resemble the sun.

Yip said the Observatory had seen a small halo at noon and again at 1pm at their Tsim Sha Tsui headquarters.

A small halo has an angular radius of 22 degrees, with a pale red lining or a purple aura at times.

She said another type of phenomenon, the large halo, also existed but was less commonly seen in Hong Kong.

A large halo has an angular radius of 46 degrees and is dimmer than the smaller version.

Yip added that the public should be careful when observing halos and always protect their eyes.

“Remember not to look at the sun directly, as strong sunlight can cause blindness,” she said.

There would be some ice crystals in the high clouds and sunlight would need to be shining through the layers JENNIFER YIP, HONG KONG OBSERVATORY