Awe-struck sky gazers were treated to a stunning phenomenon of a halo of light surrounding the moon against the dark night sky above Budapest.
Breathtaking images show a candescent halo around the moon which has a radius of approximately 22° around it – which results in a ring around 44 times larger than the moon itself.
The phenomenon is more commonly seen around the sun when it is known as a ‘sun dog’ and, like the moon halo, has a circle of light which loops around it.
The optical phenomenon forms due to ice crystals in the atmosphere in the form of thin cirrus or cirrostratus clouds present at an altitude of around 20,000 feet (6,100 metres).
During cold weather these clouds can contain millions of hexagonal ice crystals, and as light from the moon – which is just reflected sunlight – passes through the atmosphere, it refracts, or bends, in a particular way within the crystals.
Specifically, the light refracts at angles no smaller than 22° – sometimes leading the phenomenon to be called a 22° halo.
The light from the sun or moon hit the ice crystals at this minimum angle, combining to cause the appearance of a halo. These halos in general are relatively common, but it’s less common to see them form around the moon.
These images were captured over night on January 21 by a photographer near the Hungarian capital.
Lunar halos are mostly colourless because the moon itself isn’t very bright. It’s common to see a faint red colour on the inside and blue on the outside of the halo.
These colours are more noticeable in halos around the sun or ‘sun dogs’. Halos around the moon or sun have a sharp inner edge, while the outer edge is more diluted.
The shape of the halo is determined by the particular shape and position of the crystals in the clouds.
‘Sun dogs’ are more commonly seen when the sun is low in the sky and not in the middle of the day.
Dr Richard Wild, chief meteorologist at Weathernet told MailOnline: ‘Halos around the moon are caused by high level cirrus clouds above the observers head.
‘Cirrus clouds are made up of tiny ice crystals and these clouds often indicate that a forthcoming storm is imminent….the light from the moon causes these crystals to retract (splitting of light) and also reflect (glints of light from these ice crystals within the cloud).
‘These ice crystals must be oriented in a sky in a particular manner so the observer on the ground can see this phenomena.’
Halos were historically used as a form of weather forecasting.
According to the Met Office, the presence of high ‘cirrus cloud which contains the ice crystals required for haloes to form often signifies an approaching frontal system.
‘However, in many cases the front will be inactive or simply change course from the area – producing no rain.’
The clouds can also occur without a large storm approaching, so their use as a weather prediction tool is not entirely accurate.